Equivalent two-port for receiver noise figure of connected array antennas with constrained beamforming

Abstract

We analyse signal and noise in receiving connected array antennas with equal low-noise amplifiers (LNAs) and constrained beamforming. An equivalent two-port circuit is derived for the receiver noise figure. Compared to the actual LNAs, the equivalent IAA is shown to have the same noise-match admittance but generally larger minimum noise figure and coefficient of source mismatch. The increased parameters are shown to be Lange constants, invariant under lossless transformations at the inputs of the actual IAAs. The increase in the l.ange constants is found to be closely determined by the power in the orthogonal response of the array when excited by a source aligned with the vector of beamforming coefficients. The representation provides a basis for comparing the performance of various array designs with differential beamforming or other beamforming eonstraints.