On the number of signals whose directions can be estimated by an array

The dependence of direction finding accuracy and sensitivity on the number of signals and their separation is investigated. Using the Cramer-Rao lower bound on the direction-of-arrival estimates, it is shown that accuracy degrades rapidly with the number of signals if the signals are separated by less than a beamwidth. Using results on the sensitivity of the direction estimates to calibration errors, it is demonstrated that the sensitivity to calibration errors increases rapidly with the number of signals if the signals are separated by less than a beamwidth