Compact High-Isolation Multiplexer With Wide Stopband Using Spiral Defected Ground Resonator

In this paper, the compact wide-stopband diplexer/triplexer is presented. The spiral defected ground resonator (SDGR) is analyzed by using the equivalent model. Based on the symmetry of the SDGR, a diplexer and a triplexer are implemented with a miniaturized size and a wide stopband. Each filter of the channels in the diplexer or triplexer can be independently controlled and exhibits a constant fractional bandwidth. To validate the design concept, the diplexer and the triplexer are designed, fabricated, and measured. The isolation between the channels is greater than 30 dB, and the measured out-of-band suppression is greater than 10 dB in the very wide frequency range. The measured results agree well with the simulation ones.