Digital Automatic Gain Control (DAGC) for Surveillance Radar Applications: Theory and Simulation

The potential for using a digital automatic gain control (DAGC) is examined. The DAGC operates by digitally storing a clutter map of the average of past returns. This average clutter map is digitally filtered to remove small spatial variations and the resulting values are used to adjust the front end receiver gain. In contrast a traditional analog automatic gain control (AAGC) uses real time filtered feedback to control the adjustable front end gain. The physical realizability constraints of an AAGC typically result in a wider shadow zone for regions where the scan is moving from a land to sea clutter environment. It is shown that the DAGC filtering operation on the clutter map of past returns allows the spatial extent of the filter to be distributed evenly across the land-sea transition regions thereby reducing the shadow zone. The AAGC is shown to display slightly superior noise performance over the DAGC approach. Simulations of the behaviour of both systems under simplified configurations are also shown to qualitatively illustrate and clarify the tradeoffs associated with either approach.