Effectiveness of multinotch logic-product polarisation filters in radar for countering rain clutter

The applicability of multinotch logic-product (MLP) polarisation filters in radar to enhance target detection in a rain environment is investigated. The analyses use backscatter models in terms of polarisation when the environment is illuminated with circular polarisation. These models are, to a great extent, representative of the actual backscatter behaviour of aircraft targets and rain clouds. The degree of polarisation fluctuation of rain cloud returns is a parameter in the analyses. The evaluation results are presented in terms of achievable improvement in the signal-to-clutter ratio (SCR) and its dependence on the configuration and number of notches in the MLP filter. As the MLP filter is fundamentally nonlinear, the results provide insight into the upper-bound performance of such filters as a function of SCR at the input. Typically, in an environment where a linear single-notch polarisation filter gives a maximum 8 dB improvement in SCR, a nonlinear MLP polarisation filter will give at least 14 dB improvement when the SCR at the input is 0 dB