A novel mixed conventional microstrip and composite right/left-handed backward-wave directional coupler with broadband and tight coupling characteristics

A novel backward directional coupler, composed of a conventional microstrip (CμS) line and composite right/left-handed (CRLH) line, is proposed. This coupler is functionally backward but it is based on a forward-type coupling phenomenon. The coupler is shown to exhibit broad bandwidth and tight coupling characteristics. The theoretical circuit-model results are supported by full-wave and experimental evidence. A quasi 0-dB prototype with more than 50% bandwidth is demonstrated.