system temperature; efficiencies; beamforming array; noise; aperture; spillover; radiation
For an active beamforming array, standard definitions for efficiencies and system temperature are not available. We use noise considerations to generalize the single-antenna conventions for aperture efficiency, spillover efficiency, radiation efficiency, and system temperature to arrays. The treatment leads to a new noise matching efficiency that quantifies the effect of mutual coupling on amplifier noise. Numerical results for a phased array feed indicate that the noise increase caused by mutual coupling can be significant.