Bearing resolution limits for broadband signals

Analytical lower bounds on bearing accuracy for two broadband radiating sources which are located within a beamwidth at an array are presented. The power levels of the radiated signals are not necessarily known a priori. It is demonstrated that at modest signal-to-noise ratio, accuracy reductions in a multiple-source setting depend on the inverse second power of angular spacing when the power levels are known a priori, and on the inverse fourth power if the power levels are unknown a priori. The Cramer-Rao lower bounds cannot be reached, however, if the correct number of sources cannot be determined from the data. This problem is addressed by computing the probability of error in a binary hypothesis test. The results indicate the presence of a threshold below which reachability of the earlier computed bounds is clearly optimistic