A D-Band Scalable and LO-Less Time-Modulated Multibeam Active Relay Array With Broadcasting Capability for 6G Distributed MIMO Networks

This article presents a scalable D-band active reflective relay array that can enable nonline-of-sight (NLOS) wireless communication links with multibeam reception and broadcasting capabilities, targeting 6G distributed MIMO (D-MIMO) applications. By adopting two time-modulated linear periodically time-varying (LPTV) arrays at the receiving and transmitting frontends of the relay, the proposed relay concurrently receives/transmits multiple beams with multiple independent data streams from and to multiple spatially distinct wireless nodes. The local oscillator (LO)-less scheme of the proposed relay further obviates the losses and power consumption of mixers and LO distribution, ensuring a low-cost, low-complexity, and scalable relay array design. As a proof of concept, a D-band 120-GHz relay array prototype with eight-element transmitter (TX) array and eight-element receiver (RX) array is implemented in GlobalFoundaries (GF) 22 nm complementary metal-oxide–semiconductor (CMOS) FD-SOI technology. The prototype relay implementation is fully integrated with on-chip orthogonally-polarized RX/TX antenna arrays. By postprocessing the fabricated chips, substrate grooves are created at the back side of the chips to partially suppress the substrate modes and enhance the isolation between the RX and TX antenna arrays. Over-the-air (OTA) measurement results demonstrate successful 120-GHz 16-QAM 1 and 2 Gbps per beam NLOS wireless links through the relay with an EVM_rms of 6.4% and 8.9%, respectively, in the case of one external transmitting node communicating through the relay with up to six receiving nodes. The measurements also demonstrate an EVM_rms of 9.5% and 12.2%, respectively, in the case of two external transmitting nodes communicating through the relay with up to five receiving nodes.