Evaluation of Phase Coding to Mitigate Differential Reflectivity Bias in Polarimetric PAR

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 (ZDR) 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 antenna hardware alone. Hence, additional approaches are required to reduce ZDR bias due to cross-polar fields. One such approach is pulse-to-pulse phase coding of the transmitted waves. Herein, this approach is evaluated using theoretical analysis and simulated and time series data from a weather radar. The main criteria for evaluation are the bias and standard deviation of ZDR estimates. The results indicate that phase coding has the capability to significantly decrease ZDR bias without a substantial increase in the standard deviation of estimates.