AGC response and target glint

Conventionally, radar trackers use fast or `instantaneous¿¿ automatic gain control (AGC) loops for control of IF gain. The paper indicates that this practice may result in unnecessarily large errors when the tracking accuracy is limited by target `glint¿¿ effects. The analysis considers a conical scan radar which is tracking a target consisting of two, point reflectors. Two limiting cases of AGC response time are considered: `fast¿¿ AGC, when the response is much faster than fluctuations of the received signal, and `slow¿¿ AGC, when the reverse is true. It is shown that fast AGC tends to track the larger of the two sources, whereas slow AGC tracks the radar `centre of gravity¿¿ or centroid. The effects of an angle tracking error, such as might occur in tracking a fast, crossing target are also examined. The glint error probability distributions for the two AGC responses are considered and shown to be different. Fast AGC results in a small error most of the time but can result in occasional very large glint errors or `spikes¿¿ slow AGC has a somewhat larger tracking error than fast AGC some of the time but never suffers from large amplitude spikes. The analyses indicate lower probabilities of glint errors than seem to be found in practice. It is conjectured that this may arise from angle-tracking loop saturation and slow recovery, either from large glint spikes or from movement of the major target source (bright spot wander). Slow AGC may give more accurate tracking than fast AGC under these circumstances.