MICROSTRIP ELECTROMAGNETIC BANDGAP ELEMENT ON GROUND FOR HYBRID RING COUPLERS

Abstract

In this paper, a novel compact rat-race hybrid coupler incorporating square open-loop defected ground structures (SOL-DGSs) is designed and verified. As a new wave of microstrip electromagnetic bandgap element (MEBE) technology on ground plane, the bandgap characteristic of SOL-DGS is employed to reject the high-order harmonics without any additional filter and the excellent slow-wave effect of SOL-DGS is studied and utilized to reduce the circuit size in the design of the hybrid coupler. The measured insertion losses are 3.54 dB and 3.63 dB for two input ports. The isolation between port 1 and port 3 achieves around -30 dB. Furthermore, the proposed rat-race coupler successfully rejects the second, third, fourth and even fifth harmonic signals.