Multiplexers using unit-cell filters of CRLH TLs

New design method and design formulas of a filter are presented for easy construction of a multiplexer. The filter consists of only unit cell of CRLH TLs (composite right/left-handed transmission lines) and the input impedance of each channel filter is near open-circuited at the resonance frequencies of other channels. Due to the property, all the filters can be connected without any additional circuitry to build a multiplexer. Such property is due to the combination between a series and parallel resonance circuits of the unit cell. To verify the design equations, a multiplexer with two channels is designed and tested. The measured results show good agreements with prediction, showing measured insertion loss of each channel, less than 0.35 dB, matching at each port, less than -15 dB and isolation between channels, better than 30 dB.