A GENERAL-ANALYSIS AND NEW DESIGNS FOR THE HYBRID-RING DIRECTIONAL COUPLER

General expressions are presented for the scattering parameters of the hybrid-ring directional coupler, assuming only one-axis symmetry and isolation of output arms. Under the condition of matching of input arm s, the existing designs for 3-dB as well as those for arbitrary power division follow as special cases. A general design method for 3-dB cou plers is evolved, based on which a number of new designs-are presented . The calculated frequency response of the new designs has been compar ed with that of the existing ones. A new design using lambda/5 section and having an overall length 13 lambda/10 is found to be superior to the 5 lambda/4 and 7lambda/6 designs, and by virtue of its shorter len gth, is expected to have an insertion loss less than that for the comm on 3 lambda/2 design.