A wideband bandpass filter with multiple transmission zeros using a shorted stub-loaded stepped-impedance ring resonator is proposed. The resonant characteristics are investigated by even- and odd-mode analysis. In order to obtain a wideband response, the even resonant frequencies can be lowered by the shorted stub and the stepped-impedance ring. The transmission line theory is used to analyze the transmission zeros. Besides the parameters of the shorted stub and stepped-impedance ring, the transmission zeros can also be adjusted by the port separation angle. To verify the proposed design concept, a filter with 132% 3 dB fractional bandwidth and five transmission zeros in the upper stopband is designed, simulated, and fabricated. Good agreement is observed between the simulated and measured results.
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