A N260 Band 64 Channel Millimeter Wave Full-Digital Multi-Beam Array for 5G Massive MIMO Applications

In this paper, a 37-42.5GHz (N260 Band) 64 channel full-digital multi-beam array for 5G massive multiple input multiple output (MIMO) applications is developed. The multi-beam array is built on a time division duplexing (TDD) architecture in which the transmitter and receivers are independent and working separately to enable more flexible channel configuration and hardware distribution. The 64 antenna elements of the array are aligned in a way that 16 elements lie in the horizontal and 4 in the vertical direction to deliver higher beam resolution in the horizontal plane. By using cables of unequal lengths, the $16\times 4$ antenna elements are connected to a cluster of $8\times 8$ transmitters/receivers. The hardware design of the transmitters, receivers, antennas and other circuits is demonstrated, with excellent measured RF performance achieved. Furthermore, the calibration of the massive MIMO array is presented, and the influence of inequality of array feedlines on calibration accuracy in a wide bandwidth is analyzed and experimentally verified. Finally, experimental studies on single beam scanning, multiple concurrent beam generation and over-the-air (OTA) performance of the transmitting and receiving array have been done. Simulation and measurement results suggest that the array has an excellent beam-forming capability that supports beam steering and generation of multiple concurrent beams. The OTA test reveals that the array can provide high modulation and demodulation accuracy for communication.