A 140GHz Transceiver with Integrated Antenna, Inherent-Low-Loss Duplexing and Adaptive Self-Interference Cancellation for FMCW Monostatic Radar

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.