New microstrip-to-CPS transition for millimeter-wave application

This paper presents new design guidelines for microstrip-to-CPS transition for millimeter-wave applications. A circular path transition is proposed with an advantage of reducing design time as well as improving bandwidth by reducing the coupling effect of the structure especially in the 60 GHz frequency band. This new transition method is studied using 3D full-wave EM simulation tool, CST microwave studio, and measured experimentally up to 67 GHz with Agilent PNA E8361C. Two structures of microstrip-to-CPS are presented in this paper. One approach uses an asymmetric T-junction and the other approach uses a symmetric T-junction. For a back-to-back microstrip-to-CPS transition experimental measurement, insertion loss of less than 3 dB was measured over a 14% bandwidth with a center frequency of 62 GHz for the asymmetric structure and insertion loss better than 2.8 dB is obtained over a 22% bandwidth for the symmetric structure around the target frequency of 60 GHz.