Abstract: A secondary surveillance radar system in which monopulse processing is used to obtain angle estimation of azimuth bearing, involving a monopulse processor, two independent phase detectors in respective A and B channels, the arrangement being such that a log amplifier is provided in each of the respective channels and the outputs of these log amplifiers are coupled to the independent phase detectors, whereby a resultant signal is obtained giving target deviation from boresight in either direction based on differences in phase between signals appearing in the respective channels.