Compact planar diplexer using OSL-CRLH resonators

A new compact planar diplexer at 2.75 and 3.45 GHz consisting of two connected bandpass filters using open-stub loaded composite right/left-handed (OSL-CRLH) resonators has been presented. For this miniaturized diplexer, the center frequencies and bandwidths of two passbands can be determined by the sizes of their CRLH transmission line unit cells and the loaded open-circuited stubs. The measured and simulated results are in good agreement. The measured insertion losses at two center frequencies are 0.75 and 0.81 dB, and their corresponding return losses are 14.9 and 14.8 dB, respectively. The isolation of two channels is better than 35 dB.