Contents I. Introduction
Phased array transmitters (Txs) and receivers (Rxs) consisting of the multiple RF front ends and antenna arrays are adopted for the fifth-generation (5G) millimeter-wave (MMW) communications due to the high equivalent isotropic radiated power (EIRP), signal-to-noise ratio (SNR), and dynamic beamsteering with high directivity for wireless high-speed data links [1], [11]. Besides, since the completed 5G communications are the coexistence of the 5G sub-6-GHz and MMW, and the 5G MMW will launch following the earlier commercialized sub-6 GHz [12]–[15], the IF and LO frequencies of the 5G MMW front ends should be lower than 6 GHz, which could be compatible with the established sub-6-GHz system to alleviate the complexity of the coexisted system with a lower building cost [1]–[5]. Moreover, the EIRP of the -element phased array Tx increases with dB, while the SNR of the -element phased array Tx/Rx increases with dB, and the increased EIRP and SNR improve the quality of digitally modulated signals, such as the quadrature amplitude modulation (QAM) signals, for high-speed data links in a long distance [6], [16]. Therefore, for 5G MMW base station (BS) to achieve a broad area coverage, the large-scale phased array is necessary. Furthermore, because the -element phased array is composed of replicate RF front ends and antennas with regular arrangements, the scalable circuit designs and configurations of RF integrated circuit (IC) and packaged module are definitely critical and feasible to implement large-scale phased arrays with simple integration/assembly. Nevertheless, the scalable RF ICs and modules also have lower costs, which are more attractive to commercial mobile communications.
