Influence of Non-Homogeneous Earth on the Performance of High-Frequency Receiving Arrays with Electrically-Small Ground Planes
MITRE CORP BEDFORD MA
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The performance of ground-based frequency HF antenna arrays is reduced when the array elements have electrically-small ground planes. Performance degradations include 1 a decrease in directive gain near the horizon caused by earth multipath, 2 a decrease in radiation efficiency and an increase in internal noise caused by ground losses, 3 an array RMS phase error caused by exterior currents on element feed cables, and 4 an array rms phase error and beam pointing errors caused by non-uniform Fresnel reflection RMS from a non-homogeneous earth. This paper models the degradation described in 4 above. Numerical results are presented for cases of randomly-distributed and systematically-distributed earth non-homogeneities where one-half of vertically-polarized array elements are located in proximity to one type of earth and the remaining half are located in proximity to a second type of earth. The maximum rms phase errors, for the cases examined, are 18 degrees and 9 degrees for randomly-distributed and systematically-distributed non-homogeneities, respectively. The maximum beam pointing errors are 0 and 0.3 beamwidths for randomly-distributed and systematically-distributed non-homogeneities, respectively.
- Geology, Geochemistry and Mineralogy
- Electrical and Electronic Equipment