A Millimeter-Wave Dual-Feed Square Loop Antenna for 5G Communications

A millimeter-wave (mm-Wave) dual-feed square loop antenna is presented in this paper for 5G communications. It synthesizes identical far-field radiation patterns as a conventional single-feed square loop antenna. The dual-feed antenna (DFA) also simplifies or even eliminates the lossy power-combining network between the transmitter and antenna, achieving direct on-antenna power combining. The proposed antenna concept significantly improves the total radiated power and power efficiency of a wireless transmitter, particularly useful for 5G transmitters that normally require large output power to compensate the high mm-Wave path loss. Compared with antenna-array-based spatial power combining, the DFA only requires a single-antenna footprint and maintains the single-element beamwidth, ideal for mobile 5G communications. The dual-feed square loop antenna is designed and characterized at two potential 5G bands, i.e., 38.5 and 73.5 GHz. Conventional single-feed square loop antennas are implemented as reference designs. Closely matched antenna characteristics are achieved in measurement between the proposed DFA and conventional single-feed antenna. The dual-feed square loop antenna has measured broadside gain of 2.9 and 3 dBi, and fractional bandwidth of 13% and 14%, at 38.5 and 73.5 GHz, respectively. High-speed modulation test is also performed. A 4.3% error vector magnitude (EVM) with a -33.2-dBc adjacent channel leakage ratio (ACLR) for 6-Gb/s 64QAM is achieved at 38.5 GHz, and a 5.6% EVM with a -33.4-dBc ACLR for 6-Gb/s 64QAM is measured at 73.5 GHz, which demonstrates the viability of the proposed DFA for high-speed and complex modulations required by 5G communications.