Wideband 180° hybrid junctions using phase-corrected asymmetric directional couplers

A method is given for the design of 0° (180°) hybrids in TEM-mode transmission lines, the hybrids having a small phase ripple. They consist of optimum asymmetric 3dB couplers cascaded with microwave allpass phase-equaliser networks. The results, which were obtained by optimising the overall phase characteristic using a computer technique, are given in detailed tabular form, and enable hybrids with bandwidths up to at least 12:1 to be designed readily. Experimental results for a 10:1 bandwidth hybrid, having ±8.5° phase deviation from 0°, show good agreement with the theory.