Phase Code to Mitigate the Copolar Correlation Coefficient Bias in PPAR Weather Radar

One of the main challenges to the use of phased array radar for weather observations is the implementation of dual polarization with acceptable levels of cross-polar fields induced by the antenna. For example, to achieve acceptable differential reflectivity bias (i.e., less than 0.1 dB) using simultaneous transmission and reception of horizontally and vertically polarized waves, the isolation between coaxial cross-polar and copolar beams needs to be in excess of 50 dB. This presents a formidable challenge, because sufficient isolation cannot be achieved at an affordable price by the antenna hardware alone. Hence, additional approaches are required to reduce the differential reflectivity bias due to cross-polar fields. One proposed technique is a 180° pulse-to-pulse phase change of signals injected in either the horizontal or vertical ports of the transmission elements. This approach mitigates the differential reflectivity bias but may increase the bias of the copolar correlation coefficient estimates and, in some cases, the bias of the differential phase estimates. Herein, a modified phase code is proposed, which maintains the differential reflectivity bias suppression but reduces the copolar correlation coefficient and differential phase bias with respect to the originally proposed phase code.