A D-band compact rat-race coupler using novel phase inverter in standard CMOS process

This paper describes a D-band on-chip rat-race coupler using a novel phase inverter and developed in a standard CMOS process. The simple structural phase inverter which is based on the characteristic impedance and phase difference analysis has demonstrated its potential for wideband and compact millimeter-wave frequency range applications. The developed rat-race coupler using the proposed phase inverter, features a 40% size reduction and over 60% bandwidth improvement compared to conventional structures. In the complete D-band range, measured amplitude and phase imbalances for the coupler are within 0.5 dB and 15°, respectively. The port-to-port isolation is better than 25 dB in the D-band range with the highest value of 41 dB at 118 GHz. The insertion loss achieves 1.2 ± 0.3 dB and the coral size of the coupler is only 290 × 162 µm². The proposed coupler has a huge potential for integration in single-chip systems over 100 GHz.