Digital equalisation in adaptive spatial filtering for radar systems: a survey

In adaptive phased-array radar the cancellation of directional interference is limited by a number of mismatching sources; the main one is the frequency-dependent amplitude and phase mismatches between the radar receiving channels. A digital equalisation filter is needed to compensate for these mismatches. In this survey paper we describe the theory and practice of digital equaliser. We also demonstrate that the sampling rate of the analogue to digital converter has to be high enough to avoid the negative effects of folding of the interference spectrum after sampling. Several performance curves characterise the digital equaliser in terms of sampling rate and number of taps for different types of mismatches between the radar receiving channels. These curves are used to design the digital equaliser.