Some Effects of Hard Limiting in Adaptive Antenna Systems

Adaptive antennas are often implemented with the Applebaum-Howells type adaptive processor. Analog circuit versions of the Applebaum-Howells processor usually include a hard limiter between each antenna port and its correlation mixer, primarily for dynamic range compression. Brennan and Reed analyzed the effects of hard limiting, and their conclusions suggest that it does not degrade the steady-state performance of the adaptive processor. This paper shows that hard-limited processors can perform much worse than those without hard limiting in situations where the correlation matrix of array signals has two or more eigenvalues of widely differing magnitudes and when a sensitivity threshold has been designed into the processor. The practical consequence is that (depending on the processor design parameters) when the adaptive antenna encounters two or more interference signals of different power levels, the larger signal can capture the hard limiter, allowing the smaller signals to pass through the processor unattenuated. Specific examples of this effect in both phased array and multiple beam adaptive antennas are presented. (Author)