Compact and Broadband CPW-to-RWG Transition Using Stub Resonators

This paper proposes a broadband coplanar waveguide (CPW)-to-rectangular waveguide (RWG) transition using stub resonators. The reflection coefficient of the proposed transition is less than −20 dB in the frequency band ranging from 8.6 to 12.6 GHz, which almost covers the whole X-band (8.2–12.4 GHz). As compared with the miniaturized CPW-to-RWG transition using the inductance-compensated slotline, the reflection coefficient is reduced from −15 to −20 dB and the size is maintained at 8.6 mm. In order to reduce the circuit size, a compact CPW-to-RWG transition using right-angled stub resonators is proposed. The circuit size is reduced from 8.6 to 7.8 mm while the broadband response of the −20-dB reflection coefficient is maintained. In order to verify the simulation results, three back-to-back CPW-to-RWG transitions are fabricated and measured by which the measurement results agree with the simulation results.