Statistical evaluation of pulse to pulse phase coding to suppress coupling in the polarimetric radar

This paper starts by identifying one of the most challenging requirements for agile beam phased array weather radars (PARs). It is quantitative measurement of polarimetric variables to a distance of 300 km with no ambiguities in range whatsoever. Such measurement is now routine on the WSR-88D of the National Weather Service. To match this performance the weather PAR needs to operate in the mode of simultaneous transmission and reception of horizontally and vertically polarized waves (SHV mode) or quasi SHV mode. Lack of sufficient isolation on the state of the art phased array antennas precludes the SHV mode unless transmitted signals are designed to attain supplementary separation between the two orthogonal channels. A phase code sequence suggested herein is one such design that can reduce the effects of coupling at the expense of increase in the variance of estimates. This phase code is applied to a sequence having a long pulse repetition interval (as on the WSR-88D) and the statistics of estimates is analyzed. It is demonstrated that if isolation on the PAR is -25 dB and the code is applied the quality of the polarimetric variables would be equivalent to the quality of the same obtained with the WSR-88D.