Signal quality in a multibeam transmit array

Multibeam phased arrays in communications systems have the ability to transmit multiple signals in different directions. Ideally, the different signals in the different beams would be isolated and not interfere with each other. In reality, the main beams and sidelobes of the multi-beamed array interact and distort the desired signal in a given direction. Isolating the signals in the different beams is not feasible. As a result, a metric is needed to evaluate the signal quality transmitted in a beam and also the quality of the signal received in the far field.