Coupling Effects In Array-Fed Reflector Antennas With Digital Beamforming

Many modern microwave systems, for example, in the field of satellite communications, remote sensing for Earth observation or radio astronomy, employ reflector antennas with beam-shaping capabilities. A generalised description of multi-channel receiver architectures with digital beamforming, employing scattering parameter formalism is presented here. Special emphasis has been placed on noise modelling, where noise sources have been included also at the input ports of the receive amplifiers. The performance of such a system is evaluated in terms of the signal-to-noise ratio (SNR) and the signal-to-interference ratio at the beamformer output. The basis for this analysis is a design example of a reflector antenna fed by a linear patch array, whose S-parameters have been computed by means of electromagnetic simulations. In this work, two scenarios are addressed. In the first case, the effect of coupling has been neglected in the derivation of the beamforming weights. The main consequence appears to be a severely impaired interference suppression performance. In the second scenario, which has not been addressed in the literature so far, noise from the input ports of the receive amplifiers couple via the antenna radiators and can result in a loss of SNR at the beamformer output if neglected in the beamforming process.