Design of a novel 3 DB microstrip backward wave coupler using defected ground structure

Abstract

In this paper an edge coupled microstrip coupler with defected ground structure is presented. A normally 7 dB coupler designed on Alumina substrate is converted into a 3 dB coupler by cutting single rectangular slot in the ground plane encompassing the two transmission lines. Other properties of backward wave coupler remain the same, except for a tighter coupling. With this method of design optimization, it will be possible to fabricate a 3 dB coupler in compact form without strain in fabrication process. The structure is analyzed considering magnetic and electric coupling between the two transmission lines. Simulation based studies show reasonable agreement between analytical results and corresponding simulation results.