Open-loop adaptivity for rotating antennas

The application of adaptivity in the form of a sidelobe canceller to a rotating radar antenna requires that the adaptive weights employed should be updated at a rate high enough to avoid degradation due to movement of the main beam. The paper describes the design and performance of an experimental sidelobe canceller using a hybrid analogue/digital solution. A dedicated digital processor computes the weights using an open-loop algorithm and applies the results to the analogue signal path via multiplying digital-to-analogue convertors. The open-loop algorithm was chosen in order to avoid convergence problems associated with the closed-loop approach to sidelobe cancellation. A Section is included concerned with the setting-up techniques for the experimental system. Experimental results are presented, including some demonstrating effective use of MTI filters as a means of minimising the clutter contamination of samples. The use of sidelobe cancellation is shown to reduce interference entering via the 23 dB sidelobes of the radar antenna by at least some 12 dB. Data are also presented on the effects of sample size and weight revision frequency on cancellation performance.