A Millimeter-Wave Partially Overlapped Beamforming-MIMO Receiver: Theory, Design, and Implementation

This paper presents an analysis and design of a partially overlapped beamforming-multiple-input multiple-output (MIMO) architecture capable of achieving higher beamforming and spatial multiplexing gains with lower number of elements compared to conventional architectures. As a proof of concept, a four-element beamforming-MIMO receiver (RX) covering 64-67-GHz frequency band (the FCC’s newly allocated 64–71-GHz frequency band for high-speed wireless links between small cells) enabling two-stream concurrent reception is designed and measured. By partitioning the RX elements into two clusters and partially overlapping these clusters to create two three-element beamformers, both phased array (coherent beamforming) as well as MIMO (spatial multiplexing) features are simultaneously acquired. 6-bit phase shifters with 360° phase control and 5-bit VGAs with 11-dB range are designed to enable steering of the two RX clusters toward two arbitrary angular locations corresponding to two users. Fabricated in a 130-nm SiGe BiCMOS process, the RX achieves a 30.15-dB maximum direct conversion gain and a 9.8-dB minimum noise figure across 548-MHz IF bandwidth. S-parameter-based array factor measurements verify spatial filtering of the interference and spatial multiplexing in this RX chip.