A Broadband Bidirectional Four-Element Four-Beam Beamformer with Compact Floorplan in a 65nm CMOS Technology

This paper presents a broadband bidirectional four-element four-beam beamformer. By utilizing the bidirectional attenuator, and phase shifter, this design achieves a 15.5 dB gain range and a 360° phase-shifting range in both receiver (RX) mode and transmitter (TX) mode. A load state switch is integrated with this design to realize more than 30 dB signal bypass of a certain path while maintaining the input/output matching unchanged to make system-level calibration more convenient. An innovative crossover design with horizontal and vertical ground shielding is proposed to suppress the crosstalk caused by the capacitive couplings at the unavoidable cross intersection in the FC network. The measurement results demonstrate that the proposed beamformer achieves <0.12/0.26 dB root-mean-square (RMS) amplitude error and <4.2/3.9° RMS phase error in RX/TX mode at 4.5–7 GHz. To the best of our knowledge, this design is the first broadband multi-beam beamformer that can support both RX and TX modes.