A triplexer is an important component for channel separation in microwave front-end systems. This paper proposes a triplexers designed with common dual mode resonator sections have been proposed. By exploiting the variable frequency response of the stepped-impedance resonator, resonators can be shared by the three filter channels of the desired triplexer if their fundamental and the first spurious resonant frequency are properly assigned. Triplexer design method for suppressing spurious responses in the stopband by choosing the constitutive resonators with the same fundamental frequency, but staggered higher order resonant frequencies. The design concept is demonstrated by three of third order parallel-coupled bandpass filters. The bandpass filter is composed of three different stepped impedance resonators for which a general design guideline had been provided in order have the same fundamental frequency and different spurious frequencies. The measured results are in good agreement with the simulated predictions, whereby the spurious responses in the upper stopband can be suppressed below-25dB up to 14 GHz, which can be quite useful for multiband and multiservice applications in future wireless communication systems.

A novel microstrip triplexer with a common crossed resonator and some uniform impedance resonators (UIR) is proposed in this paper. The crossed resonator is theoretically analyzed and proved to be able to resonate at three different frequencies. By using the crossed resonator as the common resonator, a compact structure can be gained as no extra matching network is needed, and the number of the resonator can be reduced effectively. Moreover, a wide stopband is obtained by setting the crossed resonator and UIRs working at the same fundamental frequencies but different higher order resonant frequencies. To demonstrate the design procedure, a triplexer with a third order Chebyshev response in each channel is fabricated and measured. The measured result is in good agreement with the simulated one, showing an attenuation of 20 dB up to 8 times the first channel frequency.

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