Size reduced dual-band isolation circuits using hybrid right-handed transmission Lines for triplexers

A dual-band isolation circuit consisting of a composite right/left handed (CRLH) transmission line (TL) and a filter was previously studied, and its application to a triplexer was demonstrated. To implement designed CRLH TL, lumped elements were used for left handed (LH) part but a microstrip line was applied for right handed (RH) part. Because the size of a lumped element is relatively smaller than a microstrip line, if the size of a microstrip line would be reduced, the final size of a triplexer could be also reduced. In this paper, a hybrid RH TL, composed with lumped elements and a microstrip line, is introduced, and the theory for the hybrid RH TL and the design methodology are also explained. For verifying the concept, the triplexer, having the center frequencies 942.5 MHz, 1575 MHz, and 1842.5 MHz, is designed and fabricated.