Cramer-Rao bounds and maximum-likelihood estimation of Doppler frequency of signals received by a polarimetric radar

The exploitation of information on echo polarisation state is currently a subject of interest, owing to theoretical and technological advances as well as to the development of new radar applications. The paper presents some results relevant to the Doppler resolution bounds of signals obtainable by a polarimetric radar having orthogonally-polarised receiving channels (dual-channel receiver). Theoretical spectral-resolution accuracy based on Cramer-Rao (CR) bounds is derived in the cases of a single tone and two interfering, differently polarised pure tones. For these cases maximum-likelihood (ML) estimation is also analysed and the related performance is evaluated for the single-tone case. The results obtained show that the exploitation of polarisation by dual-channel processing of radar signals can improve the Doppler resolution of interfering signals, in comparison with the case of a single-channel (fixed polarisation) receiver.