A broadband microstrip-to-CPS transition using composite right/left-handed transmission lines with an antenna application

A broadband microstrip-to-coplanar strip (CPS) transition employing composite right/left handed (CRLH) transmission line technology is presented. The transition is based on the unique phase slope and offset control properties of the CRLH transmission line. The pairing of a microstrip delay line and the CRLH transmission line has a broadband out-of-phase characteristic, thus enabling the broadband transition between microstrip and CPS. An unbalanced and a balanced type of transition are built and tested. A 3dB insertion loss bandwidth of 85% and 80% can be achieved by connecting the transition back-to- back for the unbalanced and balanced type, respectively. To demonstrate the applicability of the proposed microstrip-to-CPS transition, a modified quasi-Yagi antenna is designed. An impedance bandwidth of 65% can be obtained, showing a 15% improvement compared to the conventional one.