Hybrid combination of tri-band isolation circuits based on conventional and double-Lorentz transmission lines for quadruplexers

Tri-band isolation circuits based on conventional transmission lines (TLs) and double-Lorentz (DL) TLs are proposed and studied. The quadruplexer composed with two types of isolation circuits has significant advantages. Because it uses less DL TLs than the quadruplexer previously studied (shown in Fig. 1(a)), it can be designed easily and demands less lumped components. Also, the advantages of the previous quadruplexer, i.e. no modification of filters and straightforward design process, remain in the proposed quadruplexer. For verifying the concept, a quadruplexer, of which center frequencies are 942.5 MHz, 1575 MHz, 2140 MHz, and 2450 MHz, is designed and fabricated. The measured results are well matched with the simulation results.