Sum-difference circuits using 0 dB and -3 dB co-directional couplers for hybrid microwave and MIMIC circuit applications

A new design approach for microstrip sum-difference ( Sigma - Delta ) Magic-T circuits is described. The technique employs entirely planar 0-dB and -3-dB codirectional quadrature couplers. A 17% bandwidth was demonstrated at the X-band from a Magic-T circuit built on a 1-in/sup 2/ alumina substrate. Multioctave 0-dB coupling is also illustrated by a computed example. Any other coupling level can be derived directly from the 0-dB codirectional coupler, thereby simplifying mask layout and significantly reducing design time. Accurate design curves for codirectional couplers on alumina substrate are given.<>