Closed-loop angle tracking of unresolved targets

An analysis is presented of the closed-loop tracking behavior of a monopulse radar in the presence of unresolved targets. Major emphasis is placed on closed-loop tracking because the majority of published curves for the angle error caused by unresolved point targets show open-loop monopulse outputs, and are not directly applicable to the closed-loop case. The approach used is to evaluate the monopulse output, in a single coordinate, as a function of beam axis position. Closed-loop tracking equilibrium points exist at beam axis positions where the angle error signal equals zero, with the local stability about each null determined by the sign and magnitude of the error signal slope at the null. Angle error signal plots are shown for a variety of cases. An equivalent block diagram of a closed-loop angle tracker is presented that includes the effect of unresolved point targets and is readily analyzed using digital control system simulation techniques