On the Impact of Frequency Discrepancy on Beamforming Performance in Millimeter-Wave Phased Array Antenna Systems

Multiple-input–multiple-output (MIMO) is a key technology used to meet the requirements of 5G systems. In millimeter-wave (mmWave) bands, directional beamforming is applied at both the transmitter and the receiver to establish an efficient radio link. The mmWave bands specified in 5G specifications range from 24.25 to 40.0 GHz. Accordingly, different countries may allocate different bands to support 5G services because of the availability of the spectrum and the countries’ radio management policies. For international roaming, user equipment (UE) must support multiband operations based on a fixed antenna hardware structure that is designed to target a specific operating band. Hence, the frequency discrepancy that results from using different operating bands causes distortion in the achieved beamforming pattern. In this article, we investigate the impact of frequency discrepancy on beamforming performance in mmWave phased array antenna systems at the UE side, considering the resultant beam pattern and interference. In this effort, we studied three major side effects—deviation of the beamforming direction, change in the effective array length, and change in the normalized interelement spacing. The numerical results indicate that a large frequency discrepancy causes severe distortion in the resultant beamforming pattern and introduces more interference into the system.