Propagation Effects for Radar & Communication Systems
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This three-day course examines the atmospheric effects that influence the propagation characteristics of radar and communication signals at microwave and millimeter frequencies for both earth and earth-satellite scenarios. These include propagation in standard, ducting, and subrefractive atmospheres, attenuation due to the gaseous atmosphere, precipitation, and ionospheric effects. Propagation estimation techniques are given such as the Tropospheric Electromagnetic Parabolic Equation Routine (TEMPER) and Radio Physical Optics (RPO). Formulations for calculating attenuation due to the gaseous atmosphere and precipitation for terrestrial and earth-satellite scenarios employing International Telecommunication Union (ITU) models are reviewed. Case studies are presented from experimental line-of-sight, over-the-horizon, and earth-satellite communication systems. Example problems, calculation methods, and formulations are presented throughout the course for purpose of providing practical estimation tools.
What You Will Learn:
- The strategic, operational and tactical levels of war.
- Operational Art and Operational Design
- The primacy of the Commander’s Intent
- Where your work contributes to national security
- Processes that determine what innovations, research and development are needed for national security
- Fundamental Propagation Phenomena. Introduction to basic propagation concepts including reflection, refraction, diffraction and absorption.
- Propagation in a Standard Atmosphere. Introduction to the troposphere and its constituents. Discussion of ray propagation in simple atmospheric conditions and explanation of effective-earth radius concept.
- Non-Standard (Anomalous) Propagation. Definition of subrefraction, supperrefraction and various types of ducting conditions. Discussion of meteorological processes giving rise to these different refractive conditions.
- Atmospheric Measurement/Sensing Techniques. Discussion of methods used to determine atmospheric refractivity with descriptions of different types of sensors such as balloonsondes, rocketsondes, instrumented aircraft and Remote Sensing.
- Quantitative Prediction of Propagation Factor or Propagation Loss. Various methods, current and historical for calculating propagation are described. Several models such as EREPS, RPO, TPEM, TEMPER and APM are examined and contrasted.
- Propagation Impacts on System Performance. General discussions of enhancements and degradations for communications, radar and weapon systems are presented. Effects covered include radar detection, track continuity, monopulse tracking accuracy, radar clutter, and communication interference and connectivity.
- Degradation of Propagation in the Troposphere An overview of the contributors to attenuation in the troposphere for terrestrial and earth-satellite communication scenarios.
- Attenuation Due to the Gaseous Atmosphere. Methods for determining attenuation coefficient and path attenuation using ITU-R models.
- Attenuation Due to Precipitation. Attenuation coefficients and path attenuation and their dependence on rain rate. Earth-satellite rain attenuation statistics from which system fade-margins may be designed. ITU-R estimation methods for determining rain attenuation statistics at variable frequencies.
- Ionospheric Effects at Microwave Frequencies. Description and formulation for Faraday rotation, time delay, range error effects, absorption, dispersion and scintillation.
- Scattering from Distributed Targets. Received power and propagation factor for bistatic and monostatic scenarios from atmosphere containing rain or turbulent refractivity.
- Line-of-Sight Propagation Effects. Signal characteristics caused by ducting and extreme subrefraction. Concurrent meteorological and radar measurements and multi-year fading statistics.
- Over-Horizon Propagation Effects. Signal characteristics caused by tropsocatter and ducting and relation to concurrent meteorology. Propagation factor statistics.
- Errors in Propagation Assessment. Assessment of errors obtained by assuming lateral homogeneity of the refractivity environment.
G. Daniel Dockery, received the B.S. degree in physics and the M.S. degree in electrical engineering from Virginia Polytechnic Institute and State University. Since joining The Johns Hopkins University Applied Physics Laboratory (JHU/APL) in 1983, he has been active in the areas of modeling EM propagation in the troposphere as well as predicting the impact of the environment on radar and communications systems. Mr. Dockery is a principal-author of the propagation and surface clutter models currently used by the Navy for high-fidelity system performance analyses at frequencies from HF to Ka-Band.
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