An ultra-wideband microstrip-to-CPW transition

A new design for an ultra-wideband microstrip-to-CPW (coplanar waveguide) transition is presented. The proposed transition provides the field and impedance matching between adjacent transmission lines by ground shaping. Clear design guidelines are provided to determine the ground shape and the transition length. As design examples, two transition designs for substrates with low (2.2) and high (10.2) dielectric constants are presented. The fabricated transitions in back-to-back configuration provide insertion loss less than 0.7 dB per transition and return loss better than 10 dB for frequencies from 7 GHz to over 40 GHz and from DC to over 20 GHz, respectively.