Spurious Passband Suppression in Compact Microstrip Rat-Race Coupler Deploying Modified Split Rings and Coupled Microstrip Lines

This manuscript presents the design of a size reduced microstrip rat-race (RR) coupler with improved spurious passband suppression performance. The coupler operates at 0.95 GHz, corresponding to 5G applications (sub-1 GHz 5G applications). The combined effect of coupled microstrip lines, slant connected split ring structure and the ring shaped defects offer deep suppression of harmonic signals beyond the passband till 4 GHz. The proposed coupler also offers 47.2% size reduction compared to a conventional RR coupler model.