Signal processing algorithm for estimation and mitigation of phase distortions in FMCW radar altimeter

Phase distortion is one of the performance deteriorating factors in Frequency Modulated Continuous Wave (FMCW) radar systems like Radar Altimeter (RA). This signal distortion, mainly introduced by the frequency synthesis units, affects the accuracy of altitude measurements in RA. Thus, the estimation and subsequent cancellation of phase distortion in real time are indispensable for improved system performance. In this work, we have developed an algorithm for estimating and mitigating phase errors. The phase distortions on the beat signal are modeled as the sum of systematic phase errors and random phase fluctuations. Phase error is estimated from the intermediate frequency signal along the reference path by adopting quadrature demodulation and Chirp Z transform (CZT) based frequency estimation technique. With the help of a suitable cancellation filter, the effect of phase error is reduced to a significant level and the efficiency of the scheme is demonstrated using simulation results.