Integrated 75–100 GHz In-Band Full-Duplex Quasi-Circulator-Based Front-End GaN MMIC

This article presents a fully integrated 75–100 GHz element-level in-band full-duplex (IBFD) front-end MMIC. The MMIC is implemented in a 40-nm HEMT GaN-on-SiC process and consists of a tunable passive quasi-circulator (PQC), power amplifier (PA), and low noise amplifier (LNA). The tunable passive circulator, consisting of three Lange couplers, uses self-interference cancellation (SIC) for circulator-like performance. With tunable loads at the isolated ports in two of the couplers, this PQC demonstrates an isolation of 30 dB from transmit to receive dependent on tunable load biasing, in addition to a return loss better than 10 dB across the band for all bias levels. The passive circulator is then integrated on a chip with a three-stage PA and a three-stage LNA, with a measured system transmit gain of 13.6 dB and a receive gain of 17 dB. The fully integrated front-end demonstrates a transmit output power of 22 dBm and a receive noise figure (NF) of 5 dB.