Noise matching in coupled antennas

A novel way to calculate the sensitivity and beam-former coefficients of a receiver consisting of coupled antennas and an optimum beamformer is presented. The low-noise amplifier (LNA) connected to each antenna is replaced with a load, which has an impedance equal to the complex conjugate of the LNA's optimum (minimum noise figure) source impedance. The sensitivity of the receiver for a given incoming wave is then proportional to the total power absorbed in these loads and the ratio of the optimum beamformer coefficients is given by the ratio of current in the loads. The sensitivity of the full receiver can therefore be calculated directly in an antenna simulation, making it easy to design and optimise low-noise receivers. It is also shown that the sensitivity can be optimised over a broad bandwidth and various scan angles by minimising the inverse of the total absorbed power. This method is much simpler than previously published methods that make use of active impedances.