A 36-91 GHz Broadband Beamforming Transmitter Architecture With Phase Error Between 1.2°-2.8° for Joint Communication and Sensing

Joint communication and sensing utilizing wide bandwidth and additional spectral bands within the 30-100 GHz range presents exciting opportunities for 6G networks. It enables improved spectrum utilization and enhanced environmental awareness. However, achieving frequency agility in a universal array interface that seamlessly operates across licensed, unlicensed, and shared bands poses significant challenges. This article addresses this challenge by presenting a crucial component, specifically the architecture of an ultra-wideband beamforming transmitter (Tx) that employs: 1) an ultra-wideband vector modulator phase shifter; 2) a broadband power amplifier (PA) enabled by inverse design method; and 3) a variable gain amplifier (VGA) with a tailored broadband frequency response. To allow for precise phase control across such a large bandwidth, a 90° hybrid-Marchand balun-based bandwidth extension network is proposed for ultra-wideband I/Q signal generation. The principle, analysis, and design of the extension network are presented in detail, leveraging a novel broadband modeling technique. The beamformer prototype implemented in 90-nm SiGe BiCMOS process maintains extremely low maximum phase error below 0.5 LSB, rms phase error of 1.24°-2.8°, and rms gain error of 0.24-0.35 dB, enabled by the proposed 5-bit phase shifter covering 36-91 GHz. The Tx also demonstrates 30-35 dB gain with 10 dB gain control, ${\text {OP}}_{\text {1 dB}}$ of 9-13.5 dBm and supports 10.8 Gbps 64-QAM modulation with -25.6 dB EVM with $P_{\text {avg}}$ of 4 dBm at 60 GHz. To the best of our knowledge, this work represents the first beamforming Tx that covers the frequency range from 5G FR2 to $W$ band, offering a fractional bandwidth of 87% (defined by the bandwidth over which the maximum phase error is below 1/2 LSB).