A millimeter-wave tunable transformer-based dual-antenna duplexer with 50 dB isolation

This paper presents a 30 GHz tunable transformer-based duplexer with dual-antenna configuration. By using orthogonal linearly-polarized antennas and the transformer-based duplexer, the transmitter and receiver duplexes the two antennas with orthogonal circularly-polarized signals. Furthermore, magnetic tuning is introduced to improve isolation in case of practical imbalances. Measurement results demonstrate an isolation of > 50 dB by the duplexer for 1 GHz bandwidth. The achieved noise figure (NF) is 4 dB and insertion loss in the TX path is 3.1 dB. The tunable duplexer occupies an active area of 0.25 mm × 0.25 mm.