A Waveguide Rat-Race Coupler with Phase Inverter Circuits Comprised of Twists

In this paper, we propose a waveguide rat-race coupler that consists of phase inverter circuits comprised of two 90° twists. In the proposed configuration, the phase differences between the lines that form the coupler are in principle independent of frequency. As a result, the coupling performances are the same at the different ports, and the low coupling amplitude difference and the low coupling phase difference are achieved. The measurement results demonstrated a return loss of 20 dB, an isolation of 30 dB, a coupling amplitude difference of +0.15/-0.15 dB, phase differences of +1/-1 deg with a bandwidth of 8% in the K-band.