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).