design of compact multi-channel diplexer using defected microstrip structure

In this paper, two compact quad-channel and six-channel diplexer are designed and fabricated using defected microstrip structure (dms). this structure is designed for the desired frequency based on the literature reviews. the proposed configuration is composed of a conventional t-junction divider with two pairs of open bended stubs and dual/tri-band filters. in designing dual band filters, a loop resonator loaded with two stepped-impedance resonator and defected microstrip structure. in addition, by adding a pair of open stubs, triband responses easily achieved without increasing the circuit size. the operating mechanism in resonance frequencies by surface current density is obtained. as a result, the multi-channel diplexer occupies a compact size of 0.13λg by 0.13λg. the measured results are fully in agreement with the simulated predictions indicating that an isolation between channels is more than 29 db.