An efficient design procedure for directional couplers based on the effective even and odd mode characteristic impedances and electrical lengths is presented. These quantities which are extracted from the scattering parameters of the overall coupler structure allow for a systematic optimization. This is useful, for instance, when designing compensated high directivity couplers or when large bandwidth performance is desired. The method is applied to optimize a 2 GHz wiggly line coupler. Measurements yield a directivity of better than 30 dB from DC to 3.5 GHz, confirming the simulation results.
