Broadband microstrip-to-CPS and microstrip-to-CPW transitions using composite right/left-handed metamaterial transmission lines
A broadband microstrip-to-coplanar strip (CPS) and a microstrip-to-coplanar waveguide (CPW) transition, both employing composite right/left-handed (CRLH) transmission line (TL) technology are presented. These metamaterial lines are known to possess unique ‘backward wave’ characteristics. The transition design concept is based on taking advantage of controlling the phase slope and offset of the CRLH-TL. The pairing of a microstrip delay line and the CRLH-TL has a broadband out-of-phase characteristic, thus enabling the broadband transition between microstrip and CPS. A 3 dB insertion loss bandwidth of 85% was achieved for a back-to-back microstrip-to-CPS transition. A broadband microstrip-to-CPW transition is implemented by adding one microstrip delay line at both sides parallel to a CRLH-TL. A 3 dB insertion loss bandwidth of 95% was obtained experimentally. To demonstrate the applicability of the proposed microstrip-to-CPS transition, a modified quasi-Yagi antenna is built and tested. An impedance bandwidth of 65% was obtained, showing a 15% bandwidth enhancement over the original antenna.