Hybrid combination of dual band isolation circuits based on conventional and CRLH transmission lines for triplexers

This paper presents dual band isolation circuits based on conventional transmission lines (TLs) and Composite Right/Left Handed (CRLH) TLs. Combination of two dual band isolation networks using CRLH TLs and one dual band isolation network based on conventional TLs can form a triplexer. Since it is not necessary to modify filters and there is no limitation to choose filters in the design concept, commercial filters can be used for a triplexer. Also, the design process is simple and straightforward. Thus there is no need to use complex numerical optimization. For verifying the design concept, a triplexer, which has 881.5MHz, 1575MHz, and 1842.5MHz center frequencies, is designed. Filters are commercial Surface Mounted (SMT) type. The simulated and measured results show that the insertion loss is less than 2dB, the return loss is larger than 14dB, and the isolation is larger than 32dB.