Estimation of Microwave Power Margin Losses Due to Earth's Atmosphere and Weather in the Frequency Range of 3-30 GHz Prepared for the United States Air Force Spectrum Efficient Technologies for Test and Evaluation Advanced Range Telemetry Edwards Air Force Base, California

This is the final report for the Air Force contract Estimation of Microwave Power Margin Losses due to Earth’s Atmosphere and Weather in the Frequency Range of 3–30 GHz (JPL task plan No. 81-6775). The goal of this study has been to perform an evaluation of radio wave propagation losses at SHF band by using available propagation models and several benchmark scenarios. The Department of Defense is exploring the possibility of occupying the microwave range of 3–30 GHz to increase bandwidth. As frequency increases, crucial changes to link power margins must be examined. Dominantly responsible for additional losses to the free space loss in the transmitted signal are atmospheric absorption, clouds, fog, and precipitation, as well as scintillation/multipath at low elevation angles. All of these losses due to the atmosphere at the studied frequency range cannot be neglected. The free space Friis Equation has been modified to add an additional term, which includes all atmospheric attenuation and fading effects. First, we completed an extensive literature search on SHF band propagation studies. Microwave propagation models from the International Telecommunication Union (ITU) are employed for this study. All attenuation figures are estimated as a function of weather condition (percent of time) and radio wave frequencies. Through detailed calculation and case study, analysis of the microwave attenuations propagating in both line of sight and trans-horizon are performed. There are significant differences in anomalous mode (ducting) propagation features between the east and the west coastal receiving stations. Terrain profiles along all directions of interest within the coastal areas and inland areas for four benchmark cases, have been analyzed in detail. Through this study, we find that at high elevation angles, atmospheric gaseous absorption and rain attenuation are the two dominant factors at SHF band. While the atmospheric gaseous absorption plays a significant role under a clear weather, heavy rainfalls can cause several tens of dB loss for a 100-km path through the rain. At very low elevation angles (< 5°), atmospheric scintillation/multipath fading becomes a very important factor. At about 50% of time, radio signals can propagate through an elevated ducting layer above the ocean up to thousand kilometers to the Pt. Mugu receiving stations. All results from this study have been plotted and tabulated as figures in this final report.