Null phase-shift instantaneous polarization filter

Normal methods of polarization filter change the phases of the target signal, and the difference of phase-shift, which is affected by the difference of the filter parameters produces the phase distortion. Based on the normal single notch and multi-notch logical product polarization filter, a new type of polarization filter named Null Phase-Shift Instantaneous Polarization (NPSIP) filter is proposed to avoid the phase distortion. The real phase (and amplitude) is kept through Linear Polarization Translation (LPT), normal polarization filter and the compensation of the phase (and the amplitude). It is indicated from the experimentally derived data that the improvement of the signal to interference ratio (SIR) achieved more than 27 dB in the experiment of HF radar for suppressing the radio interference.