A 180° Hybrid Based On Interdigitally Coupled Asymmetrical Artificial Transmission Lines

A 180deg hybrid that is based on interdigitally coupled asymmetrical artificial transmission lines has been demonstrated. The well-known c-mode-pimode analysis has been applied to its structure to derive design equations. Measurements performed on the hybrid have shown a magnitude balance of plusmn0.6 dB and return loss and isolation better than 15 dB over a 42% bandwidth. The hybrid occupies only 54% the area of a ring-shaped rat-race coupler. Furthermore, compared to the rat-race coupler and its variants, the proposed hybrid has a convenient arrangement for its output ports: they are geometrically adjacent and DC-isolated from one-another. This property addresses DC-biasing issues and eliminates the need for cross-over structures for applications in balanced mixer, balanced frequency multiplier and monopulse comparator designs