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This work presents a novel dual‐band filter based on air‐filled substrate‐integrated waveguide (SIW) cavity. Research is done on the multimode property of air‐filled SIW cavity, as a result, even mode and odd mode of TE102 are determined to produce the first passband, those of TE104 to form the second passband, meanwhile, those of TE202 as spurious modes exist in the air‐filled SIW cavity. As the resonant frequency of TE202 is close to that of TE104, a group of metal via holes is placed at where the electric field of TE202 is maximum so that TE202 does no harm to the second passband as the resonant frequency of TE202 is shifted to much higher frequency in this case. Moreover, the ratio of center frequency of the second passband to that of the first passband can be flexible adjusted for the presence of that group of metal via holes as perturbation structure. Thanks to exploiting even mode and odd mode of TE102 as well as TE104 for the design of dual‐band filter, a frequency response with two transmission poles in each passband and one transmission zero in the upper stopband of each passband are obtained, another transmission zero appears in the response as well for the presence of direct source‐load coupling. A dual‐band filter centered at 3.5 and 4.9 GHz is designed and fabricated to validate this design method, and good agreements between measured and simulated results can be observed.

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