ATI's Glossary Of Radar, Missiles and Combat Systems Terms
ACCEPTABLE DEGRADATION - The allowable reduction in system performance. For a fire control radar, the
acceptable degradation is usually expressed as a reduction in range; for example, the maximum lock-on range might be
degraded by 25 percent without loss of essential defense capability.
- ACQUISITION - A procedure by which a fire control tracking radar attains initial lock-on. Usually, the
approximate target coordinates are supplied to the tracking radar and it searches a predetermined volume of space to locate
- AEROSOLS - Solid particles dispersed in the atmosphere having resonant size particles with a high index of
refraction. The particles both scatter and absorb visual and laser directed energy so as to cut down on weapon systems
directed by these techniques.
- AFC (AUTOMATIC FREQUENCY CONTROL) - An arrangement whereby the frequency of an oscillator or the
tuning of a circuit is automatically maintained within specified limits with respect to a reference frequency. A magnetron
drifts in frequency over a period of time. The AFC of a radar makes the local oscillator shift by an equal amount so the IF
frequency will remain constant.
- AGC (AUTOMATIC GAIN CONTROL) - A method for automatically obtaining an essentially constant receiver
output amplitude. The amplitude of the received signal in the range gate determines the AGC bias (a DC voltage) which
controls the receiver gain so as to maintain a nearly constant output even though the amplitude of the input signal changes.
- AMPLIFIER - An electronic device used to increase signal magnitude or power. See also GaAs FET Amplifier,
Klystron Amplifier, Traveling-Wave Tube Amplifier.
- AMPLITUDE MODULATION (AM) - A method of impressing a message upon a carrier signal by causing the
carrier amplitude to vary proportionally to the message waveform.
- AMPLITUDE SHIFT KEYING (ASK) - A method of impressing a digital signal upon a carrier signal by causing
the carrier amplitude to take different values corresponding to the different values of the digital signal.
- ANGLE JAMMING - ECM technique, when azimuth and elevation information from a scanning fire control radar
is jammed by transmitting a jamming pulse similar to the radar pulse, but with modulation information out of phase with
the returning target angle modulation information.
- ANGULAR SEPARATION - This term is frequently used to indicate a protective (from EMI) zone for a missile.
The interfering antenna axis must be separated, throughout the critical portion of the missile flight, from the missile by the
specified angle. The vertex of the angle is at the interference source antenna.
- ANTENNA BEAMWIDTH - The angle, in degrees,
between the half-power points (-3 dB) of an antenna beam.
This angle is also nearly that between the center of the
mainlobe and the first null. The angle is given for both
horizontal and vertical planes unless the beam is circular.
When so indicated, the term may refer to the angular width
of the mainlobe between first nulls [beamwidth between first nulls (BWFN)]. See also Antenna Pattern.
- ANTENNA CROSS TALK - A measure of undesired power transfer through space from one antenna to another.
Ratio of power received by one antenna to power transmitted by the other, usually expressed in decibels.
- ANTENNA ISOLATION - The ratio of the power input to one antenna to the power received by the other. It can
also be viewed as the insertion loss from transmit antenna input to receive antenna output to circuitry.
- ANTENNA LOBING - Two lobes are created that overlap
and intercept at -1 to -3dB. The difference between the two lobes
produces much greater spatial selectivity than provided by either
lobe alone. (See also “Lobe, Antenna”).
- ANTENNA NUTATING - An antenna, as used in
automatic-tracking radar systems, consisting of a parabolic
reflector combined with a radiating element which is caused to
move in a small circular orbit about the focus of the antenna with
or without change of polarization. The radiation pattern is in the
form of a beam that traces out a cone centered on the reflector axis. The process is also known as nutating conical scanning.
- ANTENNA PATTERN - A cross section of the radiating
pattern (representing antenna gain or loss) in any plane that includes
the origin (source reference point) of the pattern. Both horizontal and
vertical polar plots are normally used to describe the pattern. Also,
termed "polar diagram" and "radiation pattern."
- ANTENNA, PENCIL-BEAM - A highly directional antenna
designed that cross sections of the major lobe are approximately
circular, with a narrow beamwidth.
- ANTI-CLUTTER CIRCUITS (IN RADAR) - Circuits which attenuate undesired reflections to permit detection
of targets otherwise obscured by such reflections.
- APERTURE - In an antenna, that portion of the plane surface area near the antenna perpendicular to the direction
of maximum radiation through which the major portion of the radiation passes. The effective and/or scattering aperture
area can be computed for wire antennas which have no obvious physical area.
- A-SCOPE - A cathode-ray oscilloscope used in radar systems to display vertically the signal amplitude as a
function of time (range) or range rate. Sometimes referred to as Range (R)-Scope.
- ASYN CHRONOUS PULSED JAMMING - An effective form of pulsed jamming. The jammer nearly matches
the pulse repetition frequency (PRF) of the radar; then it transmits multiples of the PRF. It is more effective if the jammer
pulsewidth is greater than that of the radar. Asynchronous pulsed jamming is similar to synchronous jamming except that
the target lines tend to curve inward or outward slightly and appear fuzzy in the jammed sector of a radar scope.
- ATTENU ATION - Decrease in magnitude of current, voltage, or power of a signal in transmission between two
points. May be expressed in decibels.
- AUTOMATIC FREQUENCY CONTROL - See AFC.
- AUTOMATIC GAIN CONTROL - See AGC.
- BACKWARD WAVE OSCILLATOR (BWO) - A cross-field device in which an electron stream interacts with
a backward wave on a nonreentrant circuit. This oscillator may be electronically tuned over a wide range of frequencies,
is relatively unaffected by load variations and is stable. BWO is commonly pronounced "be woe".
- BALANCED MIXERS - The two most frequently encountered mixer types are single-balanced and double-
balanced. In a double-balanced mixer, four Schottky diodes and two wideband transformers are employed to provide
isolation of all three ports.
- BALLISTIC MISSILE - Any missile which does not rely upon aerodynamic surfaces to produce lift and
consequently follows a ballistic trajectory when thrust is terminated.
- BANDPASS FILTER - A type of frequency
discrimination network designed to pass a band or Input Output
Strength range of frequencies and produce attenuation to all Strength
0 dB other frequencies outside of the pass region.
- BANDWIDTH - An expression used to define the actual operational frequency range of a receiver when it is tuned
to a certain frequency. For a radar receiver, it is the difference between the two frequencies at which the receiver response
is reduced to some fraction of its maximum response (such as 3 dB, 6 dB, or some other specified level). The frequencies
between which "satisfactory" performance is achieved.
- BARRAGE NOISE JAMMING - Noise jamming spread in frequency to deny the use of multiple radar frequencies
to effectively deny range information. Although this is attractive because it enables one jammer to simultaneously jam
several radars of different frequencies, it does have the inherent problem that the wider the jamming spread, the less
jamming power available per radar, i.e. the watts per MHz bandwidth is low.
- BATTERY, MISSILE - A missile battery consists of a missile launcher and its associated missile fire control
systems (such as a MK 11 MOD 0 Missile Launcher and two MK 74 MOD 0 Missile Fire Control Systems).
- BEACON - A system wherein a transponder in a missile receives coded signals from a shipboard radar guidance
transmitter and transmits reply signals to a shipboard radar beacon receiver to enable a computer to determine missile posi-
tion. The missile beacon transmitter and shipboard radar beacon receiver are tuned to a frequency different from that of
the guidance transmitter.
- BEAM - See Lobe, antenna. The beam is to the side of an aircraft or ship.
- BEAM, CAPTURE - See Capture Beam.
- BEAM-TO-BEAM CORRELATION (BBC) - BBC is used by frequency scan radars to reject pulse jamming and
jamming at a swept frequency. Correlation is made from two adjacent beams (pulses). The receiver rejects those targets
(signals) that do not occur at the same place in two adjacent beams.
- BEAMWIDTH - See Antenna Beamwidth.
- BEAT FREQUENCY OSCILLATOR (BFO) - Any oscillator whose output is intended to be mixed with another
signal to produce a sum or difference beat frequency. Used particularly in reception of CW transmissions.
- BINGO - The fuel state at which an aircraft must leave the area in order to return and land safely. Also used when
chaff/flares reach a preset low quantity and automatic dispensing is inhibited.
- BIPOLAR VIDEO - Unrectified (pre-detection) IF (both positive and negative portions of the RF envelope) signals
that arise from the type of detection and console display employed in pulse Doppler and MTI receivers.
- BISTATIC RADAR - A radar using antennas at different locations for transmission and reception.
- BLANKING - The process of making a channel, or device non-effective for a certain interval. Used for retrace
sweeps on CRTs or to mask unwanted signals such as blanking ones own radar from the onboard RWR.
- BOGEY - Unknown air target
- BURN-THROUGH RANGE - The ability of a radar to see through jamming. Usually, described as the point when
the radar's target return is a specified amount stronger than the jamming signal. (typical values are 6dB manual and 20 dB
- BUTT LINE - Line used for reference in measurement of left/right location. One of several aircraft references.
See also fuselage station and water line.
- CAPTURE BEAM - A wide beam incorporated in
capture transmitters of beam rider (command guided)
missile systems to facilitate gaining initial control of a
missile immediately after launch. Upon capture, the system
then centers the missile in the narrow guidance beam.
- CAPTURE TRANSMITTER - A transmitter employing a wide beam antenna to gain initial control of in-flight
missile for the purpose of centering the missile in the guidance transmitter antenna beam. See also Capture Beam.
- CARRIER FREQUENCY - The basic radio
f (Carrier Frequency) c
frequency of the wave upon which modulations are
- CAVITY - A space enclosed by a conducting surface used as a resonant circuit at microwave frequencies. Cavity
space geometry determines the resonant frequency. A storage area for oscillating electromagnetic energy.
- CENTER FREQUENCY - The tuned or operating frequency. Also referred to as center operating frequency. In
frequency diversity systems, the midband frequency of the operating range. See also Carrier Frequency.
- CHAFF - Ribbon-like pieces of metallic materials or metallized plastic which are dispensed by aircraft or ships
to mask or screen other "targets". The radar reflections off the chaff may cause a tracking radar to break lock on the target.
The foil materials are generally cut into small pieces for which the size is dependent upon the radar interrogation frequency
(approximately 1/2 wave length of the victim radar frequency). Being this length, chaff acts as a resonant dipole and
reflects much of the energy back to the radar. Also see rainbow, rope, stream chaff, and window.
- CHANNEL - A frequency or band of frequencies. In guided missile systems, an assigned center frequency and a
fixed bandwidth around it. Designates operating frequency of track radars and frequency/code assignments of X-band CW
- CHIRP - A pulse compression technique which uses frequency modulation (usually linear) on pulse transmission.
- CHIRP RADAR - See PC.
- CIRCULARLY POLARIZED JAMMING - The techniques of radiating jamming energy in both planes of
polarization simultaneously. With this method, there is a loss of 3 dB of effective power in either linear plane, and
substantial loss if the opposite sense of circular polarization is used (i.e. left vs right).
- CLUTTER, RADAR - Undesired radar returns or
echoes resulting from man-made or natural objects including
chaff, sea, ground, and rain, which interfere with normal radar
- CO-CHANNEL - This term is used to indicate that two (or more) equipments are operating on the same frequency.
- COHERENT - Two signals that have a set (usually fixed) phase relationship.
- COINCIDENCE DETECTOR - This radar video process requires more than one hit in a range cell before a target
is displayed. This prevents video interference from pulses coming from another radar, because such interference is unlikely
to occur twice in the same range cell.
- COLLIMATION - The procedure of aligning fire control radar system antenna axes with optical line of sight,
thereby ensuring that the radars will provide for correct target illumination and guidance beam positioning.
- COMMAND CODE - Modulations superimposed upon transmitter carrier signals to provide electronic instructions
to an airborne guided missile or pilotless aircraft. The receiver of the remotely guided vehicle is preset to accept only a
selected transmitter code to eliminate the possibility of the vehicle responding to commands of extraneous signals. Missile
command codes include instructions such as arm, warhead detonate, and self destruct.
- COMMAND GUIDANCE - A guidance system wherein intelligence transmitted to the missile from an outside
source causes the missile to traverse a directed flight path.
- CONICAL SCAN - See Antenna, Nutating.
- CONTINUOUS WAVE and CONTINUOUS WAVE ILLUMINATOR - See CW and CWI.
- COOPERATIVE COUNTERMEASURES - (CO-OP) Generic term for jamming the same threat radar from two
or more separate platforms that are in the same radar resolution cell.
- COUPLING FACTOR - A multiplying factor, expressed in dB, used to express the change in EM energy intensity
from a radar transmitter to a receiver. The factor includes the antenna gains and the loss (basic transmission loss) caused
by the distance between the antennas. The factor will usually be a negative dB figure (a reduction in intensity) because basic
transmission loss is always a large negative value. The antenna gains may be positive (pointed toward each other) or
negative (no main beam interactions).
- CROSS MODULATION - Intermodulation caused by modulation of the carrier by an undesired signal wave.
- CROSS POLARIZATION - or "Cross Pole", is a monopulse jamming technique where a cross-polarized signal
is transmitted to give erroneous angle data to the radar. The component of the jamming signal with the same polarization
as the radar must be very small.
- CW (CONTINUOUS WAVE) - In radar and EW systems this term means that the transmitter is on constantly;
i.e., not pulsed (100% duty cycle). These systems may frequency or phase modulate the transmitter output. A CW radar
has the ability to distinguish moving targets against a stationary background while conserving spectrum bandwidth
compared to pulsed radar requirements. A CW radar extracts accurate target range-rate data but cannot determine target
- CWI (CONT INUOUS WAVE ILLUMINATOR) - A surface or aircraft-based CW transmitter employed in
semiactive homing missile systems where the transmitter illuminates the target and the missile senses the reflected energy.
The transmitter also provides a reference signal to the missile rear receiver to allow determination of range-rate data and
target identification. CW transmitter emissions are sometimes coded corresponding to the associated missile receiver codes
to reduce the possibility of the "missile accepting commands of extraneous signals.
- DECIBEL (dB) - A dimensionless unit for expressing the ratio of two values of power, current, or voltage.
Normally, used for expressing transmission gains, losses, levels, and similar quantities.
- DECEPTION - The deliberate radiation, reradiation, alteration, absorption or reflection of electromagnetic energy
in a manner intended to mislead the enemy interpretation or use of information received by his electronic systems.
dB - See Decibel, or Decibel Section 2-4.
dBc - Decibels referenced to the carrier signal.
dBi - Decibels referenced to an isotropic radiator. (dBLi indicating linear isotropic radiator is sometimes used).
dBm - Decibels relative to 1 mW. dBm is calculated by using the ratio of some power (expressed in mW) to 1 mW.
For example, 1 mW is 0 dBm and 10 mW is +10 dBm.
dBsm - Decibel referenced to one square meter.
dBv / dB v - Decibels referenced to one volt or microvolt, i.e. 0 dBv is 1 volt or 120 dBµv.
dBW / dBµW - Decibels referenced to 1 watt or one microwatt, i.e. 0 dBW is 1 watt or 30 dBm or 60 dBµW.
- DEMODULATOR - A device employed to separate
the modulation signal from its associated carrier, also called
Second Detector. See also Detection.
- DESIGN ATION - The assignment of a fire control
radar to a specific target by supplying target coordinate data
to the radar system.
- DETECTION - Usually refers to the technique of
recovering the amplitude modulation signal (envelope)
superimposed on a carrier.
- DICKE FIX - This type of radar processing occurs in the IF amplifier. A limiter follows a wideband amplifier, and
then the signal goes to a matched filter amplifier. This discriminates against pulses that are too long (clutter) or too short
(interference). The "DICKE FIX" is a technique that is specifically designed to protect the receiver from ringing caused
by noise, fast-sweep, or narrow pulse jamming. The basic configuration consists of a broadband limiting IF amplifier,
followed by an IF amplifier of optimum bandwidth. The limit level is preset at approximately the peak amplitude of receiver
noise, the bandwidth may vary from 10 to 20 MHz, depending on the jamming environment. This device provides excellent
discrimination against fast sweep jamming (10-500 MHz), usually something on the order of 20 to 40 dB, without
appreciable loss in sensitivity. However, strong CW jamming will seriously degrade the performance of the DICKE FIX
because the CW signal captures the radar signal in the limiter.
- DIELECTRICALLY STABILIZED OSCILLATOR - The DSO uses a dielectric resonator as the frequency
determining element. When the dielectric material is properly selected and used, the variations in dielectric constant vs
temperature and the dimensions of the resonant structure vs temperature tend to cancel out, providing relatively good
frequency vs temperature stability. The DSO offers frequency accuracy and stability, low power consumption and high
reliability. Some of the commonly used materials are barium, zirconium, or tin tinates. The composition of these materials
may be controlled to achieve any frequency variation with temperature with close tolerances.
- DIODE - An electronic device which restricts current flow chiefly to one direction. See also Gunn diode, IMPATT
diode, PIN diode, point contact diode, Schottky barrier diode, step recovery diode, tunnel diode, varactor diode.
- DIODE SWITCH - PIN-diode switches provide state-of-the-art switching in mos t present-day microwave receivers.
These switches are either reflective or nonreflective in that the former reflect incident power back to the source when in the
isolated state. While both types of switches can provide high isolation and short transition times, the reflective switch offers
multi octave bandwidth in the all shunt diode configuration, while the non-reflective switch offers an octave bandwidth.
- DIPLEX - The simultaneous transmission or reception of two signals using a common feature such as a single
antenna or carrier. Typically, two transmitters operate alternately at approximately the same RF and using a common
- DIRECTIONAL COUPLER - A 4-port transmission coupling device used to sample the power traveling in one
direction through the main line of the device. There is considerable isolation (typically 20 dB) to signals traveling in the
reverse direction. Because they are reciprocal, the directional coupler can also be used to directively combine signals with
good reverse isolation. The directional coupler is implemented in waveguide and coaxial configurations.
- DIRECTIVITY - For antennas, directivity is the maximum value of gain in a particular direction. (Isotropic point
source has directivity = 1). For directional couplers, directivity is a measure (in dB) of how good the directional coupling
is and is equal to the isolation minus the coupling.
- DISH - A microwave reflector used as part of a radar antenna system. The surface is concave and is usually
parabolic shaped. Also called a parabolic reflector.
- DOPPLER EFFECT - The apparent change in
frequency of an electromagnetic wave caused by a change in
distance between the transmitter and the receiver during
- DRY RUN - A test run with aircraft/ship armament and/or EW switches off.
- DUCTING - The increase in range that an electromagnetic wave will travel due to a temperature inversion of the
atmosphere. The temperature inversion forms a channel or waveguide (duct) for the waves to travel in, and they can be
trapped, not attenuating as would be expected from the radar equation.
- DUMMY LOAD (Radio Transmission) - A dissipative but essentially nonradiating substitute device having
impedance characteristics simulating those of the antenna. This allows power to be applied to the radar transmitter without
radiating into free space. Dummy loads are commonly used during EMCON conditions or when troubleshooting a
transmitter at a workbench away from it's normal environment.
- DUPLEXER - A switching device used in radar to permit alternate use of the same antenna for both transmitting
- DUTY CYCLE - The ratio of average power to peak power, or
ratio of pulse length to interpulse period for pulsed transmitter systems.
Interpulse period is equal to the reciprocal of the pulse repetition rate.
- EFFECTIVE RADIATED POWER (ERP) - Input power to the antenna in watts times the gain ratio of the antenna.
When expressed in dB, ERP is the transmitter power (P ), in dBm (or dBW) plus the antenna gain (G ) in dB. The term
TEIRP is used sometimes and reiterates that the gain is relative to an isotropic radiator.
- EGRESS - Exit the target area.
- ELECTROMAGNETIC COUPLING - The transfer of electromagnetic energy from one circuit or system to another
circuit or system. An undesired transfer is termed EMI (electromagnetic interference).
- EMC (ELECTROMAGNETIC COMPATIBILITY) - That condition in which electrical/electronic systems can
perform their intended function without experiencing degradation from, or causing degradation to other electrical/electronic
systems. More simply stated, EMC is that condition which exists in the absence of EMI. See also Intersystem and
Intrasystem EMC tests.
- EME (ELECTROMAGNETIC ENVIRONMENT) - The total electromagnetic energy in the RF spectrum that
exists at any given location.
- EMI (ELECTROMAGNETIC INTERFERENCE) - Any induced, radiated, or conducted electrical emission,
disturbance, or transient that causes undesirable responses, degradation in performance, or malfunctions of any electrical
or electronic equipment, device, or system. Also synonymously referred to as RFI (Radio Frequency Interference).
- EMI MODEL - Usually a set of equations or logical concepts designed to illustrate the interactions, the detailed
parameters considerations, and mathematical procedures necessary for proper analysis of a given EMI situation.
- EMITTER - Any device or apparatus which emits electromagnetic energy.
- EMP (ELECTROMAGNETIC PULSE) - The generation and radiation of a very narrow and very high-amplitude
pulse of electromagnetic noise. It is associated with the high level pulse as a result of a nuclear detonation and with
intentionally generated narrow, high-amplitude pulse for ECM applications. In the case of nuclear detonations, EMP
consists of a continuous spectrum with most of its energy distributed through the low frequency band of 3 KHz to 1 MHz.
- ERROR SIGNAL - In servomechanisms, the signal applied to the control circuit that indicates the degree of
misalignment between the controlling and the controlled members. In tracking radar systems, a voltage dependent upon the
signal received from a target whose polarity and magnitude depend on the angle between the target and the center axis of
the scanning beam.
- FAST TIME CONSTANT - See FTC.
- FEET DRY / WET - Aircraft has crossed from water to shore / aircraft has crossed from shore to water.
- FERRET - An aircraft, ship, or vehicle especially equipped for the detection, location, recording, and analyzing
of electromagnetic radiations.
- FIELD STRENGTH - The magnitude of a magnetic or electric field at any point, usually expressed in terms of
ampere turns per meter or volts per meter. Sometimes called field intensity and is expressed in volts/meter or dB v/meter.
Above 100 MHz, power density terminology is used more often.
- FIRST HARMONIC - The fundamental (original) frequency.
- FREQUENCY AGILITY - A radar's ability to change frequency within its operating band, usually on a pulse-to-
pulse basis. This is an ECCM technique employed to avoid spot jamming and to force the jammer to go into a less effective
- FREQUENCY AGILITY RADAR - A radar that automatically or semiautomatically tunes through a discrete set
of operating frequencies in its normal mode of operation.
- FREQUENCY DIVERSITY RADAR - A radar system technique, employed primarily as an antijamming feature,
where the transmitter output frequency varies randomly from pulse to pulse over a wide frequency range.
- FREQUENCY RANGE - (1) A specifically designated portion of the frequency spectrum; (2) of a device, the band
of frequencies over which the device may be considered useful with various circuit and operating conditions; (3) of a
transmission system, the frequency band in which the system is able to transmit power without attenuating or distorting it
more than a specified amount.
- FREQUENCY SHIFT KEYING (FSK) - A form of FM where the carrier is shifted between two frequencies in
accordance with a predetermined code. In multiple FSK, the carrier is shifted to more than two frequencies. FSK is used
principally with teletype communications.
- "FRUIT" - In a radar beacon system, there is a type of interference called "FRUIT", caused by beacon replies to
interrogation asynchronous with the observer's interrogator. The largest amount of this interference is received through the
sidelobes of the interrogating antenna, but it can become dense enough to cause false target indications.
- FTC (FAST TIME CONSTANT) - An antijam feature employed in radar systems where receiver circuits may be
selected to provide a short time constant to emphasize signals of short duration to produce discrimination against the low
frequency components of clutter.
- FUNDAMENTAL FREQUENCY - Used synonymously for tuned frequency, carrier frequency, center frequency,
output frequency, or operating frequency.
- FUSELAGE STATION or just STATION - A reference point (usually the nose of an aircraft) used to measure or
identify fore and aft locations. One of several aircraft location designations - also see butt line and water line.
- GaAs FET AMPLIFIER - Because of their low noise, field-effect transistors are often used as the input stage of
wideband amplifiers. Their high input resistance makes this device particularly useful in a variety of applications. Since
the FET does not employ minority current carriers, carrier storage effects are eliminated giving the device faster operating
characteristics and improved radiation resistant qualities.
- GAIN: - For antennas, the value of power gain in a given direction relative to an isotropic point source radiating
equally in all directions. Frequently expressed in dB (gain of an isotropic source = 0 dB).
- GATE (RANGE) - A signal used to select radar echoes corresponding to a very short range increment. Range is
computed by moving the range gate or marker to the target echo; an arrangement which permits radar signals to be received
in a small selected fraction of the time period between radar transmitter pulses.
- GATING - (1) The process of selecting those portions of a wave which exist during one or more selected time
intervals; (2) the application of a square waveform of desired duration and timing to perform electronic switching; (3) the
application of receiver operating voltages to one or more stages only during that portion of a cycle of operation when
reception is desired. See also Gate (Range).
- GCI (GROUND-CONTROLLED INTERCEPT) - vectoring an interceptor aircraft to an airborne target by means
of information relayed from a ground-based radar site which observes both the interceptor and the target.
- GIGA - A prefix meaning 10 (times a billion). For example, gigahertz (GHz).
- GLINT (In Radar) - 1. The random component of target location error caused by variations in the phase front of
the target signal (as contrasted with Scintillation Error). Glint may affect angle, range of Doppler measurements, and may
have peak values corresponding to locations beyond the true target extent in the measured coordinate. 2. Electronic
countermeasures that uses the scintillating, or flashing effect of shuttered or rotating reflectors to degrade tracking or
seeking functions of an enemy weapons system.
- GUARDBAND - A frequency band to which no other emitters are assigned as a precaution against interference
to equipments susceptible to EMI in that band.
- GUIDANCE, BEAM RIDER - A missile guidance technique which is dependent on the missile's ability to
determine its positions with reference to the center of scan of the guidance radar beam and thus correct its trajectory on the
basis of detected errors.
- GUIDANCE CODE - A technique of modulating guidance transmitter carriers with coded pulses compatible with
the receiver code of the missile assigned that system, thus reducing the possibility of the missile accepting erroneous
commands of other transmissions.
- GUIDANCE, COMMAND - A guidance system wherein intelligence transmitted to the missile from an outside
source causes the missile to traverse a directed path in space.
- GUIDANCE, HOMING, ACTIVE - A system of homing guidance wherein both the transmitter and receiver are
carried within the missile.
- GUIDANCE, HOMING, PASSIVE - A form of homing guidance, which is dependent on a missile's ability to detect
energy emitted by the target. Frequently termed Home-On-Jam (HOJ).
- GUIDANCE, HOMING, SEMIACTIVE - A system of homing guidance wherein the missile uses reflected signals
from the target which has been illuminated by a source other than within the missile. See also CWI.
- GUIDANCE, INERTIAL - A self-contained system independent of information obtained from outside the missile,
usually using Newton's second law of motion.
- GUNN DIODE - The Gunn diode is a transferred electron device which because of its negative resistance can be
used in microwave oscillators or amplifiers. When the applied voltage exceeds a certain critical value, periodic fluctuations
in current occur. The frequency of oscillation depends primarily upon the drift velocity of electrons through the effective
length of the device. This frequency may be varied over a small range by means of mechanical tuning.
- HARMONIC - A sinusoidal component of a periodic wave or quantity having a frequency that is an integral
multiple of the fundamental frequency. For example, a component which is twice the fundamental frequency is called the
second harmonic. (the fundamental is the first harmonic, which is frequently misunderstood).
- HERTZ - The unit of frequency equal to one cycle per second.
- HOME-ON-JAM (HOJ) - See Guidance, Homing, Passive.
- HORN ANTENNA - A flared, open-ended section of waveguide used to radiate the energy from a waveguide into
space. Also termed "horn" or "horn radiator." Usually linearly polarized, it will be vertically polarized when the feed probe
is vertical, or horizontally polarized if the feed is horizontal. Circular polarization can be obtained by feeding a square horn
at a 45 angle and phase shifting the vertical or horizontal excitation by 90 .
- HYPERABRUPT VARACTOR OSCILLATOR - Due to a non-uniform concentration of N-type material (excess
electrons) in the depletion region, this varactor produces a greater capacitance change in tuning voltage and a far more linear
voltage-vs-frequency tuning curve. As a result, this device has an improved tuning linearity and low tuning voltage.
- IF (INTERMEDIATE FREQUENCY) - The difference frequency resulting from mixing (beating) the received
signal in a superheterodyne receiver with the signal from the local oscillator. The difference frequency product provides
the advantages inherent to the processing (amplification, detection, filtering, and such) of low frequency signals. The
receiver local oscillator may operate either below or above the receiver tuned frequency.
- IFF (IDENTIFICATION FRIEND OR FOE) - A system using radar transmission to which equipment carried by
friendly forces automatically responds by emitting a unique characteristic series of pulses thereby distinguishing themselves
from enemy forces. It is the "Mode IV" for the aircraft transponder. See also transponder.
- IMAGE FREQUENCY - That frequency to
which a given superheterodyne receiver is inherently
F - F = IF LO O
susceptible, thereby rendering such a receiver Antenna F - F = IF 1 LO
Desired received F = F + 2 IF 1 O
extremely vulnerable to EMI at that frequency. The signal (1050 MHz)
60 MHz IF
image frequency is located at the same frequency Image Frequency
( F = 1170 MHz ) 1
difference ( f) to one side of the local oscillator as
Lower Sideband f Upper Sideband f
the tuned (desired) frequency is to the other side. An IF = F - F = LO O ) IF = F - F = O LO )
undesired signal received at the image frequency by
F O F LO F 1 ( F = 1110 MHz) LO F 1 F LO F O
a superheterodyne receiver not having preselection
) f ) f ) f ) f
would, therefore, mix (beat) with the oscillator,
produce the proper receiver IF, and be processed in
the same manner as a signal at the desired frequency.
See also receiver selectivity.
- IMAGE JAMMING - Jamming at the image frequency of the radar receiver. Barrage jamming is made most
effective by generating energy at both the normal operating and image frequency of the radar. Image jamming inverts the
phase of the response and is thereby useful as an angle deception technique. Not effective if the radar uses image rejection.
- IMPATT DIODE - The IMPATT (IMPact Avalanche and Transit Time) diode acts like a negative resistance at
microwave frequencies. Because of this property, Impatt diodes are used in oscillators and amplifiers. Usually the
frequency range is in the millimeter wave region where other solid state devices cannot compete.
- INGRESS - Go into the target area.
- INSERTION LOSS - The loss incurred by inserting an element, device, or apparatus in an electrical/electronic
circuit. Normally expressed i n decibels determined as 10 log of the ratio of power measured at the point of insertion prior
to inserting the device (P ) to the power measured after inserting the device (P ).
- INTEGRATION EFFECT - Pulse radars usually obtain several echoes from a target. If these echoes are added
to each other, they enhance the S/N ratio, making a weak target easier to detect. The noise and interference do not directly
add from pulse to pulse, so the ratio of target strength to undesired signal strength improves making the target more
detectable. Random noise increases by the square root of the number of integrations, whereas the signal totally correlates
and increases directly by the number of integrations, therefore the S/N enhancement is equal to the square root of th e
number of integrations.
- INTERFERENCE - See EMI.
- NTERFERENCE PARAMETERS - Equipment and propagation characteristics necessary for the proper
evaluation of a given EMI situation.
- INTERFERENCE/SIGNAL RATIO = See I/S Ratio.
- INTERFERENCE THRESHOLD - The level of interference normally expressed in terms of the I/S (inter-
ference/signal) ratio at which performance degradation in a system first occurs as a result of EMI.
- INTERFEROMETER - When two widely spaced antennas are arrayed together, they form an interferometer. The
radiation pattern consists of many lobes, each having a narrow beamwidth. This antenna can provide good spatial
selectivity if the lobe-to-lobe ambiguity can be solved such as using amplitude comparison between the two elements.
- INTERMODULATION - The production, in a nonlinear element (such as a receiver mixer), of frequencies cor-
responding to the sums and differences of the fundamentals and harmonics of two or more frequencies which are transmitted
through the element; or, the modulation of the components of a complex wave by each other, producing frequencies equal
to the sums and differences of integral multiples of the component frequencies of the complex wave.
- INTERSYSTEM EMC - EMC between the external electromagnetic environment (EME) and an aircraft with it's
installed systems. Generally, only system BIT must operate properly on the carrier deck while all system functions must
operate properly in the operational EME.
- INTRASYSTEM EMC - EMC between systems installed on an aircraft, exclusive of an external environment.
- INVERSE CON SC AN - One method of confusing a radar operator or fire control radar system is to provide
erroneous target bearings. This is accomplished by first sensing the radar antenna scan rate and then modulating repeater
amplifier gain so the weak portion of the radar signal is amplified by the jammer, while the strong portion is not, so the
weapons systems will fire at some bearing other than the true target bearing. The angle deception technique is used to break
lock on CONSCAN radars.
- INVERSE GAIN - Amplification, inverse modulation, and re-radiation of a radar's pulse train at the rotation rate
of the radar scan. Deceives a conical scanning radar in angle.
- ISOTROPIC ANTENNA - A hypothetical antenna which radiates or receives energy equally in all directions.
- I/S RATIO (INTERFERENCE-TO-SIGNAL RATIO) (ISR) - The ratio of electromagnetic interference level to
desired signal level that exists at a specified point in a receiving system. The ratio, normally expressed in dB, is employed
as a tool in prediction of electronic receiving system performance degradation for a wide range of interference receiver input
levels. Performance evaluations compare actual I/S ratios to minimum acceptable criteria.
- JAFF - Expression for the combination of electronic and chaff jamming.
- JAMMING - The deliberate radiation, reradiation, or reflection of electromagnetic energy with the object of
impairing the use of electronic devices, equipment, or systems by an enemy.
- JINK - An aircraft maneuver which sharply changes the instantaneous flight path but maintains the overall route
of flight. More violent than a weave.
- JITTERED PRF - An antijam feature of certain radar systems which varies the PRF consecutively, and randomly,
from pulse to pulse to prevent enemy ECM equipment from locking on, and synchronizing with, the transmitted PRF. PRF
is synonymous with pulse repetition rate (PRR).
- KILO - A prefix meaning 10 (times one thousand). For example, kilohertz.
- KLYSTRON AMPLIFIER - An electron beam device which achieves amplification by the conversion of periodic
velocity variations into conduction-current modulation in a field-free drift region. Velocity variations are launched by the
interaction of an RF signal in an input resonant cavity and are coupled out through an RF output cavity. Several variations
including reflex and multi cavity klystrons are used.
- KLYSTRON, MULTICAVITY - An electron tube which employs velocity modulation to generate or amplify
electromagnetic energy in the microwave region. Since velocity modulation employs transit time of the electron to aid in
the bunching of electrons, transient time is not a deterrent to high frequency operations as is the case in conventional elec-
tron tubes. See also Velocity Modulation.
- KLYSTRON, REFLEX - A klystron which employs a reflector (repeller) electrode in place of a second resonant
cavity to redirect the velocity-modulated electrons through the resonant cavity. The repeller causes one resonant circuit to
serve as both input and output, which simplifies the tuning operation. This type of klystron is well adapted for use as an
oscillator because the frequency is easily controlled by varying the position of the repeller. See also Velocity Modulation.
- LEAKAGE - Undesired radiation or conduction of RF energy through the shielding of an enclosed area or of an
- LENS, RADAR (MICROWAVE) - The purpose of any such lens is to refract (focus) the diverging beam from an
RF feed into a parallel beam (transmitting) or vice versa (receiving). The polarization is feed dependent.
- LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION (LASER) - A process of generating
coherent light. The process utilizes a natural molecular (and atomic) phenomenon whereby molecules absorb incident
electromagnetic energy at specific frequencies, store this energy for short but usable periods, and then release the stored
energy in the form of light at particular frequencies in an extremely narrow frequency-band.
- LIMITING - A term to describe that an amplifier has reached its point of saturation or maximum output voltage
swing. Deliberate limiting of the signal is used in FM demodulation so that AM will not also be demodulated.
- LITTORAL - Near a shore.
- LOBE, ANTENNA - Various parts of the antenna's
radiation pattern are referred to as lobes, which may be 2nd Side Lobe 1st Side Lobe
subclassified into major and minor lobes. The major lobe is
the lobe of greatest gain and is also referred to as the main
lobe or main beam.
- LOCAL OSCILLATOR FREQUENCY - An internally generated frequency in a superheterodyne receiver. This
frequency differs from the receiver operating frequency by an amount equal to the IF of the receiver. The local oscillator
frequency may be designed to be either above or below the incoming signal frequency.
- LOG VIDEO - This receiver process, generally implemented in the IF, compresses the dynamic range of the signal
so both weak and strong signals are displayed without changing the gain setting. Output voltage can be calibrated in
volts/dB of input power.
- LONG PULSE MODE - Many pulsed radars are capable of transmitting either long or short pulses of RF energy.
When the long pulses of RF energy are selected manually (or sometimes automatically), the radar is said to be operating
in the long pulse mode. In general, "long pulse mode" is used to obtain high average power for long-range search or
tracking, and "short pulse mode" gives low average power for short-range, high-definition, tracking or search.
- LOOSE DEUCE - General term for two aircraft working in mutual support of each other.
- LORO (LOBE-ON-RECEIVE-ONLY) - A mode of operation generally consisting of transmitting on one non-
scanning antenna system and receiving the reflected energy on another scanning system (The receiver could be TWS,
Conical, or monopulse).
- MACH NUMBER - The ratio of the velocity of a body to the speed of sound in the medium that is being
considered. In the atmosphere, the speed of sound varies with temperature and atmospheric pressure, hence, so does mach
- MAGNETIC ANOMALY DETECTOR - A means of detecting changes in the earth's magnetic field caused by
the presence of metal in ships and submarines.
- MAGNETRON - A magnetron is a thermionic vacuum tube which is constructed with a permanent magnet forming
a part of the tube and which generates microwave power. These devices are commonly used as the power output stage of
radar transmitters operating in the frequency range above 1000 MHz and are used less commonly down to about 400 MHz.
A magnetron has two concentric cylindrical electrodes. On a conventional magnetron, the inner one is the cathode and the
outer one is the anode. The opposite is true for a coaxial magnetron.
- MAGNETRON OSCILLATOR - A high-vacuum tube in which the interaction of an electronic space charge and
a resonant system converts direct current power into ac power, usually at microwave frequencies. The magnetron has good
efficiency, is capable of high power outputs, and is stable.
- MATCHED FILTER - This describes the bandwidth of an IF amplifier that maximizes the signal-to-noise ratio
in the receiver output. This bandwidth is a function of the pulsewidth of the signal.
- MDS (MINIMUM DETECTABLE/DISCERNIBLE SIGNAL) - The receiver input power level that is just
sufficient to produce a detectable/discernible signal in the receiver output. The detectable term is interchangeable with S
and the discernable term is interchangeable with MVS.
- MEACONING - A system receiving radio signals and rebroadcasting them (or just transmitting) on the same
frequency to confuse navigation. The meaconing station attempts to cause aircraft to receive inaccurate range or bearing
- MEATBALL - Visual light "ball" seen in Fresnel lens optical landing system (FLOLS) by pilot during carrier or
Navy field landing. Used as a reference to determine if flight path is high or low.
- MEGA - A prefix meaning 10 (times one million). For example megahertz (MHz)
- MICROVOLT PER METER - A commonly used unit of field strength at a given point. The field strength is
measured by locating a standard receiving antenna at that point, and the "microvolts per meter" value is then the ratio of
the antenna voltage in microvolts to the effective antenna length in meters. Usually used below 100 MHz. Above 100
MHz, power density terminology is normally used.
- MICROWAVE AMPLIFICATION BY STIMULATED EMISSION OF RADIATION (MASER) - A low-noise
radio-frequency amplifier. The emission of energy stored in a molecular or atomic system by a microwave power supply
is stimulated by the input signal.
- MISS DISTANCE - Used variously in different contexts. The distance from the missile to the geometric center of
the aircraft, or the closest point of approach (CPA) of the missile to any portion of the aircraft such as the aircraft nose or
telemetry pod, etc.
- MISSILE SYSTEMS FUNCTIONS - Examples of missile system functions are: "acquisition" (ability to lock-on
a desired target); "tracking" of a target; "guidance" of a missile toward a target; "illumination" of a target so that a homing
missile can home on the reflected RF illumination; and "command" signal transmission to a missile to cause it to arm, to
detonate, to commence homing, or to destroy itself.
- MIXERS - See Balanced and Schottky Diode Mixers.
- MODULATION - The process whereby some characteristic of one
wave is varied in accordance with some characteristic of another wave. The
basic types of modulation are angle modulation (including the special cases
of phase and frequency modulation) and amplitude modulation. In missile
radars, it is common practice to amplitude modulate the transmitted RF
carrier wave of tracking and guidance transmitters by using a pulsed wave
for modulating, and to frequency module the transmitted RF carrier wave
of illuminator transmitters by using a sine wave.
- MODULATION , AMPLITUDE - This type of modulation changes the amplitude of a carrier wave in responses
to the amplitude of a modulating wave. This modulation is used in radar and EW only as a switch to turn on or turn off the
carrier wave; i.e., pulse is a special form of amplitude modulation.
- MODULATION, FREQUENCY - The frequency of the modulated carrier wave is varied in proportion to the
amplitude of the modulating wave and therefore, the phase of the carrier varies with the integral of the modulating wave.
See also Modulation.
- MODULATION, PHASE - The phase of the
modulated carrier is varied in proportion to the amplitude of
the modulating wave. See also Modulation.
- MONOPULSE - A type of
tracking radar that permits the extracting of tracking error
information from each received pulse and offers a reduction
in tracking errors as compared to a conical-scan system of
similar power and size. Multiple (commonly four) receiving
antennas or feeds are placed symmetrically about the center
axis and operate simultaneously to receive each RF pulse
reflected from the target. A comparison of the output signal
amplitude or phase among the four antennas indicates the
location of the target with respect to the radar beam center
line. The output of the comparison circuit controls a servo
system that reduces the tracking error to zero and thereby causes the antenna to track the target.
- MOS (MINIMUM OPERATIONAL SENSITIVITY) - The minimum signal which can be detected and
automatically digitally processed by a radar without human discrimination.
- MTI (MOVING TARGET INDICATOR) - This radar signal process shows only targets that are in motion.
Signals from stationary targets are subtracted out of the return signal by a memory circuit.
- MULTIPATH - The process by which a transmitted signal arrives at the receiver by at least two different paths.
These paths are usually the main direct path, and at least one reflected path. The signals combine either constructively or
destructively depending upon phase, and the resultant signal may be either stronger or weaker than the value computed for
- MULTIPLEX - Simultaneous transmission of two or more signals on a common carrier wave. The three types of
multiplex are called time division, frequency division, and phase division.
- MULTIBAND RADAR - A type of radar which uses simultaneous operation on more than one frequency band
through a common antenna. This technique allows for many sophisticated forms of video processing and requires any
jammer to jam all channels at the same time in order to be effective.
- MVS (MINIMUM VISIBLE SIGNAL) - The minimum input pulse signal power level which permits visibility of
the output pulse, such as on a radar A-scope display. This level is determined by initially setting the input level above the
visible detection threshold, and then slowly decreasing the amplitude.
- NOISE FIGURE, RECEIVER - A figure of merit (NF or F) of a system given by the ratio of the signal-to-noise
ratio at the input, S / N , divided by the signal-to-noise ratio at the output, S / N .
- NOISE JAMMING - A continuous random signal radiated with the objective of concealing the aircraft echo from
the enemy radar. In order for it to be effective, it must have an average amplitude at least as great as the average amplitude
of the radar echo. There are three major categories of noise jamming which are grouped by how jamming power is
concentrated: Spot, barrage, and swept jamming. (See individual definitions)
- NONCOHERENT - Two signals that have no set phase relationship.
- NOTCH - The portion of the radar velocity display where a target disappears due to being notched out by the zero
Doppler filter. If not filtered (notched), ground clutter would also appear on the display. A notch filter is a narrow band-
reject filter. A "notch maneuver" is used to place a tracking radar on the beam of the aircraft so it will be excluded.
- NULL, ANTENNA PATTERN - The directions of minimum transmission (or reception) of a directional antenna.
See also Lobe, Antenna.
- NULL FILL - The nulls in an antenna pattern may
be reduced (filled) by using a second ancillary (spoiler)
antenna whose pattern is such that it fills in the nulls of the
main antenna pattern.
- NUTATION - As applied to current missile system
radars, this term refers to the mechanical motion of an
antenna feed to produce a conical scan (fixed polarization) by the main beam of a tracking antenna, thus providing a means
of developing tracking error signals. See also Antenna, Nutating. By analogy, "Nutation" also is used to denote th e
electrical switching of the quadrants of a seeker antenna. See also Interferometer. The effect is similar to that of a conical
- NUTATOR - A motor-driven rotating antenna feed used to produce a conical scan for a tracking radar. See also
Antenna, Nutating. Also, the electrical circuits necessary to effect nonmechanical conical scans. See also Nutation.
- OPERATIONAL CONSTRAINTS - Limitations on operating procedures in order to prevent interference between
missile systems on a ship or between missile systems in a formation of ships under operational conditions. These limitations
consist of such things as limited frequency bands or channels in which the radars may be tuned, limited sectors of space into
which radar beams may be pointed, limits on minimum spacing between ships, limits on what codes may be used by radars
and missiles on each ship, and limits on minimum interval between firing of certain missiles.
- OSCILLATORS - Devices which generate a frequency. See also Backward Wave, Dielectrically Stabilized
Oscillator, Hyperabrupt Varactor Oscillator, Magnetron Oscillator, Varactor Tuned Oscillator, and YIG tuned oscillator.
- OSCILLATOR, LOCAL - See Local Oscillator Frequency.
- PALMER SCAN - Conical scan superimposed on another type of scan pattern - usually a spiral pattern.
- PARAMETER - A quantity which may have various values, each fixed within the limits of a stated case or discus-
sion. In the present case, some examples of parameters; would be: radar frequency, limited by the tuning range of the radar;
missile range, limited by the maximum operating range of the missile; or a missile code, limited by the number of codes
available and by the codes that the ship radars are set up to operate on.
- PASSIVE ANGLE TRACKING - Tracking of a target using radiation from the target (such as jamming), with no
radiation from the radar itself. Only angular tracking is possible under these conditions since no measurement of time of
travel of radiation to the target is possible, as is required to obtain target range.
- PC (PULSE COMPRESSION) - The process used in search and tracking pulse radars whereby the transmitted
pulse is long, so as to obtain high average transmitter output power, and the reflected pulse is processed in the radar receiver
to compress it to a fraction of the duration of the transmitted pulse to obtain high definition and signal strength
enhancement. Pulse compression may be accomplished by sweeping the transmitted frequency (carrier) during the pulse.
The returned signal is then passed through a frequency-dependent delay line. The leading edge of the pulse is therefore
delayed so that the trailing edge catches up to the leading edge to produce effectively a shorter received pulse than that
transmitted. Pulse compression radars are also referred to as CHIRP radars. Other more sophisticated pulse compression
techniques are also possible and are becoming more popular.
- PENCIL BEAM - A narrow circular radar beam from a highly directional antenna (such as a parabolic reflector).
- PHASED ARRAY RADAR - Radar using many antenna elements which are combined in a controlled phase
relationship. The direction of the beam can be changed as rapidly as the phase relationships (usually less than 20
microseconds). Thus, the antenna typically remains stationary while the beam is electronically scanned. The use of many
antenna elements allows for very rapid and high directivity of the beam(s) with a large peak and/or average power. There
is also a potential for greater reliability over a conventional radar since the array will fail gracefully, one element at a time.
- PIN DIODE - A diode with a large intrinsic (I) region sandwiched between the P- and N- doped semiconducting
regions. The most important property of the PIN diode is the fact that it appears as an almost pure resistance at RF. The
value of this resistance can be varied over a range of approximately one-10,000 ohms by direct or low frequency current
control. When the control current is varied continuously, the PIN diode is useful for attenuating, leveling and amplitude
modulation of an RF signal. When the control current is switched on and off or in discrete steps, the device is useful in
switching, pulse modulating, and phase shifting an RF signal.
- POINT CONTACT DIODE - This was one of the earliest semiconductor device to be used at microwave
frequencies. Consisting of a spring-loaded metal contact on a semiconducting surface, this diode can be considered an early
version of the Schottky barrier diode. Generally used as a detector or mixer, the device is somewhat fragile and limited to
- POLARIZATION - The direction of the electric field (E-field) vector of an electromagnetic (EM) wave. The most general case is elliptical polarization with all others being special cases. The E-field of an EM wave
radiating from a vertically mounted dipole antenna will be vertical and the wave is said to be vertically polarized. In like
manner, a horizontally mounted dipole will produce a horizontal electric field and is horizontally polarized. Equal vertical
and horizontal E-field components produce circular polarization.
- PORT - The left side of a ship or aircraft when facing the bow (forward)
- POWER (AVERAGE) FOR PULSED RADARS - Average power for a pulse radar is the average power
transmitted between the start of one pulse and the start of the next pulse (because the time between pulses is many times
greater than the pulse duration time, the average power will be a small fraction of peak power).
- POWER OUTPUT - Power output of a transmitter or transmitting antenna is commonly expressed in dBW or dBm.
- POWER (PEAK) FOR PULSED RADARS - Peak power for a pulsed radar is the power radiated during the actual
pulse transmission (with zero power transmitted between pulses).
- POWER FOR CW RADARS - Since the power output of CW transmitters (such as illuminator transmitters)
usually have a duty cycle of one (100%), the peak and average power are the same.
- POWER DENSITY - The density of power in space expressed in Watts/meter , dBW/m , etc. Generally used in
measurements above 100 MHz. At lower frequencies, field intensity measurements are taken.
- PPI-SCOPE - A radar display yielding range and azimuth (bearing) information via an intensity modulated display
and a circular sweep of a radial line. The radar is located at the center of the display.
- PROPAGATION - In electrical practice, the travel
of waves through or along a medium. The path traveled by
the wave in getting from one point to another is known as
the propagation path (such as the path through the atmosphere in getting from a transmitting antenna to a receiving antenna,
or the path through the waveguides and other microwave devices in getting from an antenna to a receiver).
- PULSE COMPRESSION - See PC.
- PULSED DOPPLER (PD) - A type of radar that combines the features of pulsed radars and CW Doppler radars.
It transmits pulses (instead of CW) which permits accurate range measurement. This is an inherent advantage of pulsed
radars. Also, it detects the Doppler frequency shift produced by target range rate which enables it to discriminate between
targets of only slightly different range rate and also enables it to greatly reduce clutter from stationary targets. See also
- PULSE LENGTH - Same meaning as Pulsewidth.
- PULSE MODULATION - A special case of amplitude modulation wherein the carrier wave is varied at a pulsed
rate. Pulse Modulation - The modulation of a carrier by a series of pulses generally for the purpose of transmitting data.
The result is a short, powerful burst of electromagnetic radiation which can be used for measuring the distance from a radar
set to a target.
- PULSE REPETITION FREQUENCY (PRF) - The rate of occurrence of a series of pulses, such as 100 pulses per
second. It is equal to the reciprocal of the pulse spacing (T) or PRT. (PRF = 1/T = 1/PRI). Sometimes the term pulse
repetition rate (PRR) is used.
- PULSE REPETITION FRE QUENCY (PRF) STAGGER - The technique of switching PRF (or PRI) to different
values on a pulse-to-pulse basis such that the various intervals follow a regular pattern. This is useful in compensating for
blind speeds in pulsed MTI radars. Interpulse intervals which differ but follow a regular pattern.
- PULSE REPETITION INTERVAL (PRI) or TIME (PRT) - Time between the beginning of one pulse and the
beginning of the next.
- PULSE SPACING - The interval of time between the leading edge of one pulse and the leading edge of the next
pulse in a train of regularly recurring pulses. See also Pulse Repetition Frequency. Also called "the interpulse period."
- PULSEWIDTH - The interval of time between the
leading edge of a pulse and the trailing edge of a pulse
(measured in microseconds for the short pulses used in
radar). Usually measured at the 3 dB midpoint (50-percent
power or 70% voltage level) of the pulse, but may be
specified to be measured at any level.
- QUANTIZE - The process of restricting a variable to a number of discrete values. For example, to limit varying
antenna gains to three levels.
- RADAR - Radio detection and ranging.
- RADAR CROSS SECTION - A measure of the radar reflection characteristics of a target. It is equal to the power
reflected back to the radar divided by power density of the wave striking the target. For most targets, the radar cross section
is the area of the cross section of the sphere that would reflect the same energy back to the radar if the sphere were
substituted. RCS of sphere is independent of frequency if operating in the far field region.
- RADAR RANGE EQUATION - The radar range equation is a basic relationship which permits the calculation
of received echo signal strength, if certain parameters of the radar transmitter, antenna, propagation path, and target are known.
- RADAR TRIGGER KILL - see Trigger Kill, Radar
- RADIATION PATTERN - See Antenna Pattern.
- RADIO FREQUENCY - See RF.
- RADIO FREQUENCY INTERFERENCE - See RFI.
- RAIL KEEPING - Ability of countermeasures to keep the missile on the launch rail, i.e., prevent launch.
- RAINBOW - A technique which applies pulse-to-pulse frequency changing to identifying and discriminating
against decoys and chaff.
- RANGE CELL - In a radar, a range cell is the smallest range increment the radar is capable of detecting. If a radar
has a range resolution of 50 yards and a total range of 30 nautical miles (60,000 yds), there are: 60000/50 = 1,200 range
- RANGE GATE - A gate voltage used to select radar echoes from a very short range interval.
- RANGE GATE PULL OFF (RGPO ) - Deception technique used against pulse tracking radars using range gates.
Jammer initially repeats the skin echo with minimum time delay at a high power to capture the AGC circuitry. The delay
is progressively increased, forcing the tracking gates to be pulled away ("walked off") from the target echo. Frequency
memory loops (FML's), or transponders provide the variable delay.
- RANGE RATE - The rate at which a radar target is changing its range with respect to the radar (in feet per second
for example). Note that this rate is not the same as target velocity unless the target is moving straight toward or straight
away from the radar.
- RANGE SCOPE - See A-Scope or PPI.
- RECEIVER BANDWIDTH - The difference between the F 1 F 2
limiting frequencies within which receiver performance in respect to 1.0
some characteristic falls within specified limits. (In most receivers
Gain of 0.707 corresponds to
a 3 dB decrease and is also
this will be the difference between the two frequencies where the called the half power points
intermediate frequency (IF) amplifier gain falls off 3 dB from the gain
at the center IF frequency.) See also Receiver Selectivity.
- RECEIVER SELECTIVITY - The degree to which a
receiver is capable of differentiating between the desired signal
Wide receiver bandwidth Narrow receiver bandwidth
and signals or interference at other frequencies. (The narrower undesired signal will passs increases signal rejection
the receiver bandwidth, the greater the selectivity.)
- REFLECTION - The turning back (or to the side) of a
Desired Signal Undesired Signal
radio wave as a result of impinging on any conducting surface
which is at least comparable in dimension to the wavelength of
the radio wave.
- RESOLUTION - In radar, the minimum separation in angle or in range between two targets which the radar is
capable of distinguishing.
- RF (RADIO FREQUENCY) - A term indicating high frequency electromagnetic energy.
- RFI (RADIO FREQUENCY INTERFERENCE) - Any induced, radiated, or conducted electrical disturbance or
transient that causes undesirable responses or malfunctioning in any electrical or electronic equipment, device, or system.
Same as EMI. Not to be confused with the logistic term ready for issue (also RFI).
- RING AROUND - A condition in which a repeater jammer's total gain, from receiver antenna to transmitter
antenna, exceeds the antenna isolation resulting in the repeater amplifying it's own internal noise. Akin to positive feedback
in an amplifier that causes unwanted oscillations.
- RING AROUND (RADAR-TO-MISSILE) - The condition where radio frequency interference signals from a
transmitter of one missile radar enter the receiving circuits of a missile under the control of another missile radar.
- RING AROUND (RADAR-TO-RADAR) - The condition where radio frequency interference signals from a
transmitter of one radar enter the receiving circuits of another radar.
- ROPE - An element of chaff consisting of a long roll of metallic foil or wire which is designed for broad, low-
frequency response. See Chaff.
- R-SCOPE - (RANGE SCOPE) See A-scope or PPI.
- SAFETY OF FLIGHT (SOF) TEST - A flight test to verify that a new or modified subsystem will not cause a
major problem with the aircraft, i.e., interference can occur, but will not be such that required navigational systems will fail
or which might potentially cause the loss of an aircraft under all normally expected weather conditions.
- SCAN - To transverse or sweep a sector or volume of airspace with a recurring pattern, by means of a controlled
directional beam from a radar antenna. See also “Antenna, nutating”.
SCHOTTKY BARRIER DIODE - The Schottky barrier diode is a simple metal-semiconductor boundary with no
P-N ju nction. A depletion region between the metal contact and the doped semiconductor region offers little capacitance
at microwave frequencies. This diode finds use as detectors, mixers, and switches.
- SCHOTTKY DIODE MIXER - The mixer is a critical component in modern RF systems. Any nonlinear element
can perform the mixing function, but parameters determining optimal mixing are noise figure, input admittance, and IF noise
and impedance. The Schottky diode is particularly effective because of its low noise figure and nearly square law
- SCHOTTKY DIODE SWITCH - Standard P-N diodes are limited in switching ability at high frequencies because
of capacitance provided by the minority carriers. The Schottky diode overcomes this problem by use of the metal-
semiconductor junction with inherently low carrier lifetimes, typically less than 100 picoseconds.
- SEARCH RADAR - A radar whose prime function is to scan (search) a specified volume of space and indicate the
presence of any targets on some type of visual display, and, in some cases, to provide coordinates of the targets to a fire
control system to assist in target acquisition and tracking.
- SEEKER - The seeker consists of circuitry in a homing missile which detects, electronically examines, and tracks
the target; provides data for controlling the flight path of the missile; and provides signals for destroying the missile or for
detonating it at intercept. (The seeker function is similar to that of an interferometer.)
- SELF-SCREENING JAMMING (SSJ) - Each aircraft carries it's own jamming equipment for it's own protection.
- SENSITIVITY - The sensitivity of a receiver is taken as the minimum signal level required to produce an output
signal having a specified signal-to-noise ratio. See also Minimum Visible Signal and Minimum Discernible Signal (MDS).
- SENSITIVITY TIME CONTROL - See STC.
- SENSOR - The receiver portion of a transmitter/receiver pair used to detect and process electromagnetic energy.
- SHIELDING - The physical arrangement of shields for a particular component, equipment, or system, (A shield
is a housing, screen, or other material, usually conducting, that substantially reduces the effect of electric or magnetic fields
on one side of the shield upon devices or circuits on the other side.) Examples are tube shields, a shielded enclosure or
cabinet for a radar receiver, and the screen around a screen
Lower Upper Lower Upper
- SHORT PULSE MODE - See Long Pulse Mode. Sideband Sideband Sideband Sideband
- SIDEBAND - A signal either above or below the
carrier frequency, produced by the modulation of the carrier
Carrier modulated by a sine wave Carrier amplitude modulated by a pulse
wave by some other wave.
- SIDELOBE - See Lobe, Antenna.
- SIGNAL STRENGTH - The magnitude of a signal at a particular location. Units are volts per meter or dBV/m.
- SIGNATURE - The set of parameters which describe the characteristics of a radar target or an RF emitter and
distinguish one emitter from another. Signature parameters include the radio frequency of the carrier, the modulation
characteristics (typically the pulse modulation code), and the scan pattern.
- SILICON CONTROLLED SWITCH - A P-N-P-N device able to operate at sub-microsecond switching speeds
by the application of gate signals. Because it is a four layer device, this switch is also known as a tetrode thyristor.
- SLANT POLARIZATION - Technique of rotating a linear antenna 45 so it can receive or jam both horizontal
and vertical polarization although there is a 3 dB loss.
- SOLID STATE STAMO - A stable master oscillator constructed using transistors and other solid state devices
as opposed to vacuum tubes. See also STAMO.
- SPECTRUM - The distribution of power versus frequency in an electromagnetic wave. See also Spectrum
Signature Analysis and illustrations under Sideband.
- SPECTRUM ANALYZER - An electronic device for automatically displaying the spectrum of the electromagnetic
radiation from one or more devices. A cathode ray tube display is commonly used to display this power-versus frequency
spectrum. For examples of two types of displays, see illustrations under Sideband.
- SPECTRUM SIGNATURE ANALYSIS - The analysis of the electromagnetic radiation from an electronic device
to determine the relative power in each sideband, harmonic, and spurious emission compared to the carrier frequency. This
particular distribution (or spectrum) is peculiar to the device and can identify this type of device, thereby acting as an identi-
- SPECTRUM WIDTH (TRANSMITTER) - The difference between the frequency limits of the band which contains
all the spectrum frequency components of significant magnitude.
- SPOILER ANTENNA - An antenna used to change (spoil) the antenna pattern of a second antenna so as to reduce
the nulls in the pattern of the second antenna. See also Null Fill .
- SPOKING (RADAR) - Periodic flashes of the rotating radial display. Sometimes caused by mutual interference.
- "SPOOFING" - A type of deception by using an electronic device to transmit a "target" echo. The spoofing
transmitter must operate at the same frequency and PRF as the radar to be deceived. The radar main pulse triggers the
spoofing transmitter which, after a delay, transmits a false echo.
- SPOT JAMMING - Narrow frequency band jamming concentrated against a specific radar at a particula r
frequency. The jamming bandwidth is comparable to the radar bandpass. Can deny range and angle information.
- SPURIOUS EMISSION - Electromagnetic radiation transmitted on a frequency outside the bandwidth required
for satisfactory transmission of the required waveform. Spurious emissions include harmonics, parasitic emissions, and
intermodulation products, but exclude necessary modulation sidebands of the fundamental carrier frequency.
- SQUINT ANGLE - The angular difference between the
Main Lobe Axis
axis of the antenna mainlobe and the geometric axis of the antenna
reflector, such as the constant angle maintained during conical scan Squint Angle
Reflector Geometric Axis
as the mainlobe rotates around the geometric axis of the reflector.
- STAGGERED PRF - Staggered PRF allows an increase in MTI blind speeds such that no zeros exist in the velocity
response at lower velocities. In a two-period mode, the usual "blind speed" or occurrence of a zero in the velocity response
is multiplied by a factor which is a function of the ratio of the two repetition periods.
- STAMO (STABLE MASTER OSCILLATOR) - A very stable (drift free) oscillatory used to provide a precise
frequency for transmission and for comparison with the reflected radar signal returned to the receiver, such as in a Doppler
radar where a precise difference between transmitted and received signals must be measured to determine accurately the
- STAND-FORWARD JAMMING - A method which places the jamming vehicle between the enemy sensors and
- STAND-IN JAMMING (SIJ) - Similar to stand-forward jamming but usually using an UAV with a lower powered
jammer instead of a jammer aircraft.
- STAND-OFF JAMMING (SOJ) - An ECM support aircraft orbits in the vicinity of the intended target. As the
fighter-bomber pilot starts his strike penetration, the ECM aircraft directs jamming against all significant radars in the area.
This technique provides broad frequency band ECM without affecting performance of the strike aircraft.
- STARBOARD - The right side of a ship or airplane when facing the bow (forward).
- STC (SENSITIVITY TIME CONTROL) - Gain control that reduces the radar receiver gain for nearby targets as
compared to more distant targets. STC prevents receiver saturation from close-in targets.
- STEP RECOVERY DIODE - A charge-controlled switch which ceases current conduction so rapidly that it can
be used to produce an impulse. Cyclic operation of the diode can produce a train of impulses which when used with a
resonant circuit can produce a single frequency output at any harmonic of the pulse frequency.
- STERADIAN - Unit of solid angle. An entire sphere has 4 steradians.
- STREAM CHAFF - Operational technique of dropping large quantities of chaff for a continuous period of time.
This results in a "ribbon" or "stream" of returns many miles in lengths on radarscopes. The penetrating strike force can then
use the resulting chaff corridor to mask their penetration.
- SUBHARMONIC - A frequency which is an integral submultiple of another frequency. For example, a sine wave
whose frequency is one-third of the frequency of another sine wave is called the third subharmonic. (3 MHz is the third
subharmonic of 9 MHz).
- SUPERHETERODYNE RECEIVER - A receiver that mixes the incoming signal with a locally generated signa]
(local oscillator) to produce a fixed, low intermediate frequency (IF) signal for amplification in the IF amplifiers.
- SUPPRESSION - Elimination or reduction of any component of an emission, such as suppression of a harmonic
of a transmitter frequency by band rejection filter.
- SUPPRESSION OF ENEMY AIR DEFENSES (SEAD) - Activity which neutralizes, destroys, or temporarily
degrades enemy air defense systems by using physical attack or electronic means (SEAD pronounced "seed" or "C add").
- SUSCEPTIBILITY - The degree to which an equipment or a system is sensitive to externally generated
- SWEPT JAMMING - Narrowband jamming which is swept through the desired frequency band in order t o
maximize power output. This technique is similar to sweeping spot noise to create barrage jamming, but at a higher power.
- SWITCHES - See also Diode Switch, Silicon Controlled Switch, Schottky Diode Switch.
- SYNCHRODYNE - A klystron mixer amplifier stage in a transmitter, where two signal frequencies are applied
as inputs and a single amplified signal is taken out.
- TARGET SIZE - A measure of the ability of a radar target to reflect energy to the radar receiving antenna. The
parameter used to describe this ability is the "radar cross section" of the target. The size (or radar cross section) of a target,
such as an aircraft, will vary considerably as the target maneuvers and presents different views to the radar. A side view
will normally result in a much larger radar cross section than a head-on view. See also Radar Cross Section.
- TERMINAL IMPEDANCE: - The equivalent impedance as seen by the transmitter/receiver.
- TERRAIN BOUNCE - Term for jamming that is directed at the earth's surface where it is reflected toward the
threat radar. Reflected jamming creates a virtual image of the jamming source on the earth as a target for HOJ missiles.
- THERMISTOR - A resistor whose resistance varies with temperature in a defined manner. The word is formed
from the two words "thermal" and "resistor,"
- THRESHOLD ISR - The interference to signal ratio (ISR) at which the performance of a receiver starts undergoing
degradation. It must be determined by tests.
- TRACKING RADAR - A radar whose prime function is to track a radar target and determine the target coordinates
(in range and angular position) so that a missile may be guided to the target, or a gun aimed at the target.
- TRACKING RADAR RECEIVER - These are of two primary types: conical scan and monopulse.
(1) The conical scan system directs the radar signal in a circle around the target. The radar paints this circle 15 to 40 times
per second. As the target moves out of the center of this circle, the radar develops aim error voltages and re-aims the
antenna. (2) The monopulse system directs four beams at the target simultaneously. The target is in the middle of the four
beams. If the target is not in the center, the radar return develops an aim error voltage to re-aim the antenna.
- TRACK WHILE SCAN (TWS) RADAR - Although it is not really a tracking radar in the true sense of the word,
it does provide complete and accurate position information for missile guidance. In one implementation it would utilize two
separate beams produced by two separate antennas on two different frequencies. The system utilizes electronic computer
techniques whereby raw datum is used to track an assigned target, compute target velocity, and predict its future position,
while maintaining normal sector scan. Most aircraft use only a single antenna.
- TRADE-OFF TABLES - A set of tables showing the various combinations of two or more variables that are related
in that making one variable better will make the other variable worse. The trade-off helps find the best solution considering
all combinations. (For example, how a no-interference condition can be maintained if two emitter platforms are brought
close together, if at the same time the frequency separation between their radar transmitters is increased.)
- TRANSIENT - A phenomenon (such as a surge of voltage or current) caused in a system by a sudden change in
conditions, and which may persist for a relatively short time after the change (sometimes called ringing).
- TRANSPONDER - A transmitter-receiver capable of accepting the electronic challenge of an interrogator and
automatically transmitting an appropriate reply. There are four modes of operation currently in use for military aircraft.
Mode 1 is a nonsecure low cost method used by ships to track aircraft and other ships. Mode 2 is used by aircraft to make
carrier controlled approaches to ships during inclement weather. Mode 3 is the standard system used by commercial aircraft
to relay their position to ground controllers throughout the world. Mode 4 is IFF. See also IFF.
- TRAVELING-WA VE TUBE AMPLIFIER - The TWT is a microwave amplifier capable of operation over very
wide bandwidths. In operation, an electron beam interacts with a microwave signal which is traveling on a slow wave helical
structure. The near synchronism of the beam and RF wave velocities results in amplification. Bandwidths of 3:1 are
possible. Operation at high powers or at millimeter wavelengths is possible at reduced bandwidths.
- TRIGGER KILL (RADAR) - A method employed to momentarily disable certain radar system circuits to reduce
or eliminate RF emissions which may cause an EMI/EMC or RADHAZ situation such as on the deck of a ship.
- TUNNEL DIODE - The tunnel diode is a heavily doped P-N junct ion diode that displays a negative resistance over
a portion of its voltage-current characteristic curve. In the tunneling process, electrons from the p-side valence bands are
able to cross the energy barrier into empty states in the N-side conduction band when a small reverse bias is applied. This
diode is used as a microwave amplifier or oscillator.
- UPLINK - The missile guidance signal which passes midcourse correction command guidance intelligence from
the guidance radar site to the missile.
- VARACTOR DIODE - A P-N junction employi ng an external bias to create a depletion layer containing very few
charge carriers. The diode effectively acts as a variable capacitor.
- VARACTOR TUNED OSCILLATOR - A varactor diode serves as a voltage-controlled capacitor in a tuned circuit
to control the frequency of a negative resistance oscillator. The major feature of this oscillator is its extremely fast tuning
speed. A limiting factor is the ability of the external voltage driver circuit to change the voltage across the varactor diode,
which is primarily controlled by the driver impedance and the bypass capacitors in the tuning circuit.
- VELOCITY GATE PULL-OFF (VGPO) - Method of capturing the velocity gate of a Doppler radar and moving
it away from the skin echo. Similar to the RGPO, but used against CW or Doppler velocity tracking radar systems. The
CW or pulse doppler frequency, which is amplified and retransmitted, is shifted in frequency (velocity) to provide an
apparent rate change or Doppler shift.
- VELOCITY MODULATION - Velocity modulation is modification of the velocity of an electron beam by
alternately accelerating and decelerating the electrons at a frequency equal to the input frequency. Thus, the electrons are
segregated in bunches, each bunch causing a cycle or current as it passes an output electrode. The velocity of the electrons
is thus a function of the modulation voltage. See also Klystron, Multicavity and Klystron, Reflex.
- VICTIM - A receiver (radar or missile) that suffers degradation due to ECM or EMI effects.
- VIDEO - Receiver RF signals that have been converted (post detection) into a pulse envelope that can be seen when
applied to some type of radar visual display; also used to describe the actual display itself (such as the video on an A-scope).
- WARM - Acronym for Wartime Reserve Mode. Any mode of operation of a radar or ECM that is held in reserve,
and never used, except in actual combat.
- WATER LINE - A reference line used for vertical measurements. When used with an aircraft it is usually the
ground with the landing gear extended normally. One of several aircraft location designations, also see butt line and
- WAVEGUIDE - A transmission line consisting of a hollow conducting tube of arbitrary geometry (usually
rectangular, but may be circular) within which electromagnetic waves may propagate.
- WAVELENGTH - The distance traveled by a wave in one period (the period is the time required to complete
one cycle). = c/f. In the atmosphere, electromagnetic waves travel at c, the speed of light (300 million meters per second
or 30 cm/nsec). At 5 GHz, one wavelength = 6 cm. At 10 GHz, one wavelength = 3 cm.
- WAVEMETER - An instrument for measuring the frequency of a radio wave. The wavemeter is a mechanically
tunable resonant circuit. It must be part of a reflection of transmission measurement system to measure the maximum
response of a signal. Below 20 GHz, the wavemeter has been replaced by the frequency counter with much greater accuracy
and ease of use.
- WEAVE - An aircraft maneuver that smoothly changes the instantaneous flight path but maintains the overall route
of flight. Not as violent as a jink.
- WET RUN - A test run with ship / aircraft armament and/or EW switches on.
- WILD WEASEL - USAF aircraft (F-4Gs during Desert Storm) used for suppression of enemy air defense (SEAD)
- WINDOW - WWII name for chaff
- YIG TUNED OSCILLATOR - A YIG (yttrium iron garnet) sphere, when installed in the proper magnetic
environment with suitable coupling will behave like a tunable microwave cavity with Q on the order of 1,000 to 8,000.
Since spectral purity is related to Q, the device has excellent AM and FM noise characteristics.
- ZENER DIODE - A diode that exhibits in the avalanche-breakdown region a large change in reverse current over
a very narrow range in reverse voltage. This characteristic permits a highly stable reference voltage to be maintained across
the diode despite a wide range of current.