Polarization of radar echoes, including aircraft, precipitation and terrain

Abstract

The paper records the results of measurements made during 1950–53 on the echoing properties of various radar targets using two radars which radiated circularly polarized radiation, one on X-band (wavelength 3.2cm) and the other on Q-band (wavelength 8.6mm): the design and operating procedure of these radars, which received both hands of circular polarization, are described. Although the tests on each frequency were carried out independently, the results are in substantial agreement. The power reflected by aircraft was divided equally between right-hand and left-hand circular polarization within limits of 3 dB either way. Thus the loss on changing from a plane polarized radar to a circularly polarized radar is 2.5dB, since the plane polarized radar return loses about 0.5dB to the orthogonal plane of polarization. Hence the echoes from aircraft cannot consist mainly of simple single-bounce echoes from curved surfaces. Terrain echoes behave similarly to aircraft echoes, except that the fluctuation rate is much more variable; among terrain echoes there are some prominent single-bounce or vertically polarized targets which can be identified with manmade structures. Rain echoes are 28dB less for the common transmitting/receiving aerial than for an orthogonal (opposite-hand) receiving aerial at X-band: at Q-band the corresponding figure is 17dB. For the melting band the figures are 17dB and 8dB, respectively. These results indicate a substantial degree of suppression of rain echoes compared with aircraft echoes at both frequencies.