Error modelling and calibration procedure for a full-angle monopulse receiver

The authors discuss how the angular accuracy of a monopulse radar results from the combined effect of several error sources, namely: (i) deviation of the antenna sum (Σ) and difference (Δ) radiation patterns from a nominal design shape; (ii) amplitude and phase mismatching and mutual coupling between the Σ and Δ monopulse receiver channels; (iii) receiver noise; (iv) target radar cross-section (RCS) fluctuation model. The analysis is carried out with reference to a full-angle monopulse processing scheme which is known to have the advantage of handling signals with comparable dynamic range and to be less sensitive to amplitude mismatching between the receiver channels. In order to minimise the effect of the aforementioned error sources (i) and (ii), an original procedure of calibration is proposed, based on an open-loop approach consisting of the following steps: (a) the injection of a test signal at receiver inputs; (b) the measurement of the corresponding digitised data in the signal processor; (c) the computation of proper correction coefficients; (d) the application of the correction equations to the digitised samples of the received signals during the radar normal operation