A microstrip diplexer based on dual-mode resonators

A miniature third-order microstrip diplexer comprising a traditional $T$-shaped dual-mode resonator at the input and one dual-mode resonator of original design, with regular strip conductors split from one end, at the output of each channel. The passband formation in each channel of the diplexer involves two resonances of the lowest modes of one split microstrip resonator and the resonance of one of the two modes of the $T$-shaped microstrip resonator. The proposed device is simple to manufacture and allows the central frequencies and bandwidths in each channel to be varied within broad limits. The good prospects of the proposed microstrip diplexer are confirmed by the high characteristics of its working prototype.