Quad-Band Rat-Race Coupler With Suppression of Spurious Pass-Bands

In this letter, a quad-band rat-race (RR) coupler with spurious pass-band suppression is presented. A new design method of laterally offset dual ring (LODR) resonator backed with concentric dual split ring (CDSR) slots has been deployed. The transmission line model of the laterally offset dual-ring resonator has been characterized and presented. The prototype offers quad-band response at 1.45, 3.8, 4.3, and 6.3 GHz, corresponding to International Maritime Satellite Organisation (INMARSAT), Satellite C-band downlink, aeronautical radio navigation, and Satellite C-band uplink applications respectively. It offers 180° coupler characteristics at each of the four design frequencies and also provides 30.4% size reduction compared to a conventional RR coupler operating at the lowest band. This RR coupler suppresses spurious pass-bands beyond the fourth band. The proposed model has been fabricated and tested to validate the performance.