An interdigitated coupler with defect ground structure

In this paper, an interdigitated coupler with defect ground structure in the coupling position is presented. Compared to the conventional interdigitated coupler, the proposed coupler loosens restrictions of the coupling-line width and space between coupling lines. As a result, the requirement of fabricating accuracy for the new coupler is lowered. In addition, with the introduction of suitable defect ground structure, the bandwidth of the coupler can be improved substantially. The designed 3-dB coupler has the coupling strength of -3dB±0.8dB within the passband of 2~8GHz, while both the isolation response and the return loss are lower than -20dB.