Dual band isolation circuits based on CRLH transmission lines for triplexer application

This paper presents a novel dual band isolation network using a Composite Right/Left Handed (CRLH) transmission line (TL) and its application to a triplexer. This triplexer consists of three dual band isolation networks composed of a CRLH transmission line, and each network is connected to a bandpass filter. Each network allows the RF signal to flow at the center frequency of their corresponding filter, however, it prevents signal flow at the center frequencies of two other filters. As a result, combined three networks can accomplish the required characteristics for a triplexer. This triplexer has two significant advantages. First, there is no restriction in choosing filters. Any filters can be used in this concept and it is not necessary to modify characteristics of the filters. Second, the design process of the triplexer is straightforward and no complex numerical analysis process is needed. Hence, design and manipulation of a triplexer are straightforward. For demonstrating the concept, a triplexer, having 1GHz, 1.8GHz, and 2.4GHz frequency bands, is designed and fabricated. The measured results show good agreement with the simulation results.