Compact filtering magic-T using a hybrid microstrip-cavity structure

This letter introduces a filtering magic-T based on a hybrid microstrip-cavity structure. TE011 and TE101 modes of the cavity are generated by the two perpendicular input microstrip lines to form the filtering responses. Because of the orthogonality of the feeding lines and the two resonant modes, in- and out-of-phase output currents and high port isolations are achieved. The measured filtering responses of the two input ports are in good agreement with each other and possess high-frequency selectivity. The isolations of the input and output ports are below 41 and 22 dB, respectively. Moreover, benefiting from the hybrid microstrip-cavity structure, only two cavity resonators are employed, which realizes compact size.