On broadband adaptive beamforming for tactical radio systems

An adaptive antenna array has the ability to change its pattern automatically in response to changes in the signal environment. In this paper we have examined, through extensive simulations, the capabilities and limitations with two broadband adaptive beamforming. A broadband circular 16-element antenna array intended for the frequency range 200-500 MHz has been constructed at FOI. Tapped-delay lines are used to achieve broadband properties. The first algorithm is a constrained minimum variance beamformer while the second minimizes the mean square error between a reference signal and the output of the beamformer. We show how various parameters (e.g. signal strength, bandwidth, the number of taps and samples) influence the performance of the beamformer. Further, the constrained minimum variance beamformer has been examined for sensitivity to discrepancies between the look-direction and the direction of the desired signal. Methods to improve the robustness of the beamformers, i.e., diagonal loading, noise eigenvalue equalization, and derivative constraints, have also been examined Finally, we illustrate the sensitivity of the adaptive beamforming algorithms against unknown phase and gain errors in the receiver channels.