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Abstract
In this paper, a new compact dual-band bandpass filter with multi-Spurious Suppression is proposed, which is composed of stub-loaded step impedance resonators. The stub-loaded SIRs are used to decrease the dimensions of the resonators and increase unwanted resonant frequencies. The even mode Resonance frequencies can be controlled with stub-loaded section; therefore the second resonance frequency can be tuned for WLAN application. A transmission zero is also created by stub-loaded section and used to suppress the unwanted spurious responses. The length of coupling and the gap size between stub-loaded SIRs are two freedom degrees for determining the realizable fractional bandwidth of the two passbands. A complete design procedure of dual-passband responses and suppression of spurious responses is described in detail. A third-order filter is designed and fabricated. The measured results show a rejection level of 24 dB up to more than 20 GHz (8.16f 1). Simulation and test results are in good agreement with each other.