A 140GHz Transceiver with Integrated Antenna, Inherent-Low-Loss Duplexing and Adaptive Self-Interference Cancellation for FMCW Monostatic Radar
Xibi Chen, Muhammad Ibrahim Wasiq Khan, Xiang Yi, Xingcun Li, Wenhua Chen, Jianfeng Zhu, Yang Yang, Kenneth E. Kolodziej, Nathan M. Monroe, Ruonan Han
Abstract
Sub-THz radars in CMOS are attractive in vital-sign and security-sensing applications, due to their low cost, small size, and high resolution. The commonly used bistatic configuration, however, leads to serious beam misalignment between TX and RX, when large-aperture lenses/mirrors are used for longer range and higher spatial precision. As shown in [1], a 4mm physical separation between TRX antennas at 122GHz can cause 6° TRX beam misalignment, exceeding the 3dB beamwidth of the 29dBi-directivity beam. Monostatic radars are, therefore, preferred in those applications, when sufficient TRX isolation is achieved to avoid saturating the RX. Prior monostatic radars [2]–[6] adopt hybrid/directional couplers for passive TRX duplexing, but at the cost of 3dB+3dB insertion loss inherent to couplers. In [3], such extra loss is mitigated through two sets of hybrid couplers and a quad-feed circularly polarized antenna. Note that in all full-duplex systems, antenna interface mismatch degrades the TRX isolation; in [3], the achieved 26dB isolation relies on excellent antenna matching enabled by backside radiation through a silicon lens. In comparison, frontside radiation allows for low-cost packaging and pairing with compact, large-aperture planar lens, but it causes much degraded antenna matching, hence is challenging for monostatic operation. In this paper, we present a 140GHz monostatic radar in CMOS, which not only circumvents the 6dB inherent insertion loss of couplers, but also facilitates the highly-desired frontside radiation through an adaptive self-interference cancellation (SIC), achieving 33.3dB of total TRX isolation.