Carrier Aggregation for Phased-Array Analog Beamforming with Beam Squint

To aggregate or not to aggregate, that is the question. Analog beamforming with phased arrays is a promising technique for 5G wireless communication in millimeter wave bands. However, beam squint degrades the performance of analog beamforming for wideband systems with a large number of antennas, because the array response varies with frequency. In this paper, we show that carrier aggregation for phased-array analog beamforming should take beam squint into consideration. Specifically, we study the optimal beam alignment to maximize channel capacity, and demonstrate that, with sufficient band separation, focusing on only one band outperforms carrier aggregation. Approximations are developed for a system with two bands to determine the critical values of system parameters like band separation, angle of arrival, and signal-to-noise ratio beyond which it is preferable not to aggregate.