Asymmetric Ultra-Wideband Microstrip-to-Coplanar Stripline Transition

A new design method for an asymmetric microstripto-coplanar stripline (CPS) transition based on the analytical electromagnetic model is presented. The cross section at each stage of the transition is analyzed through conformal transformation, and the corresponding line impedance is calculated. Then, the ground linewidth on the substrate bottom is adjusted to form an optimal Klopfenstein impedance taper. To demonstrate the design method, a transition between a 50-Ω microstrip line and a high-impedance CPS line (147 Ω) was implemented. Good transition performance with more than 10-dB return loss and less than 1-dB insertion loss was obtained for frequency ranges of 6-40 GHz.