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An HF Antenna for Oblique Propagation Having Approximately Circular Polarization over Appreciable Frequency and Vertical-Angle Intervals
STANFORD UNIV CA STANFORD ELECTRONICS LABS
The report describes the design of a pair of HF antennas, one horizontally and one vertically polarized, whose gains and directivity patterns are reasonable alike over the range of elevation angles useful for oblique ionospheric propagation over typical one-hop distances. Means are given for obtaining the proper phasing for approximating circular polarization at a designated elevation angle and over a substantial frequency interval. The design must take into account the differing reflecting properties of ordinary ground for vertically-polarized and horizontally-polarized incident waves, and the variations of these properties with radio frequency. The theoretical performance of a cross-polarized antenna pair of one particular configuration is described. It is shown that satisfactory performance should be obtained over ground having electrical properties within the range usually encountered, though not when the reflecting surface is fresh water, sea water or ground covered by a conducting screen. Experimental results are given which tend to confirm that the crossed antenna pair does operate in the manner predicted by the theory. Construction details are furnished.
Approved for public release; distribution is unlimited.
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