Parameters of Coplanar Diretional Couplers with Lower Ground Plane

Conformal mapping techniques are used to give design information for coplanar directional couplers with lower ground plane. The analysis leads to analytic closed-form expressions for the coupler parameters and gives the limit beyond which a dominating coplanar waveguide behaviour cannot be assured. Experimental results on a 8.2 dB coupler designed from these calculations have shown reasonably good agreement with predictions.