MAXIMUM-LIKELIHOOD SIGNAL ESTIMATION FOR POLARIZATION-SENSITIVE ARRAYS

We consider the problem of separating and estimating the waveforms of superimposed signals received by a polarization-sensitive array. Signa l estimation is accomplished by a two-step maximum likelihood procedur e: (i) The directions of arrival and polarization parameters of all th e signals are estimated. (ii) The estimated signal is obtained as a li near combination of the array outputs, with weights which are computed from the estimated direction/polarization parameters. The objective o f this paper is to analyze the quality of the estimated signal in term s of the output signal-to-interference ratio (SIR) and output signal-t o-noise ratio (SNR). Closed-form expressions are derived for the outpu t SIR and SNR of a general diversely polarized array. By evaluating th ese expressions for selected test cases it is shown that polarization- sensitive arrays can provide significantly higher output SIR and SNR t han uniformly polarized arrays. The performance improvement is especia lly significant for closely spaced sources with sufficiently different polarization characteristics.