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, tri-band 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.