New matching circuits for microstrip triplexers are proposed based on half-wavelength tapped-connected (or fed) stepped-impedance resonators. The stepped-impedance resonators play important roles for the matching circuits, either to serve as a through pass at the center frequency of a bandpass filter or to provide a short circuit at the center frequency of another bandpass filter. First, three tapped-connected stepped-impedance resonators together with suitable branch transmission lines are utilized to develop the matching circuits for a microstrip triplexer. The design procedure for these matching circuits is much simpler than that for the conventional triplexer structures due to the use of tapped-connected stepped-impedance resonators. Second, to reduce the number of stepped-impedance resonators and to improve the spurious resonances associated with the proposed matching circuits, modified matching circuits for the triplexer are also proposed. Agreement between measured and simulated results is observed and supports the usefulness of the design procedure.

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Abstract-This study presents new Wilkinson power dividers using compact stepped-impedance structures and capacitive loads to achieve the required power splitting. This approach can produce additional transmission zeros and effectively suppress the desired stopbands because shunt open stubs realize capacitive loads. This study proposes two equal-split dividers and two unequal-split dividers. For the first equal-split case, one shunt open stub forms the needed capacitor in each transmission path, creating one additional transmission zero in each path. To obtain one more transmission zero in each transmission path, the second Wilkinson power divider uses two shunt open stubs in each path to achieve the same capacitor value as the first divider. This study also tests unequal-split dividers with one and two transmission zeros in each path to confirm that compact stepped-impedance transmission lines and shunt-to-ground capacitors can be utilized in unequal power division.

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