A compact triple‐mode (TM) bandpass filter (BPF) is designed based on the proposed dual capacitively‐loaded (DCL) substrate‐integrated waveguide (SIW) resonator. Two identical T‐shaped grounded striplines are inserted into a square SIW cavity to generate a capacitively loading effect without damaging cavity surface integrity, which contributes to maintaining EM‐shielding capability. By adjusting the size and position of the DCL structure, the first three resonant modes, including TE101, TE201, and TE301 are easily controlled to design a TM‐BPF. A transmission zero (TZ) is introduced by the grounded striplines and flexibly controlled. TZ is tuned to suppress the TE102 mode to acquire a wide upper rejection band. Furthermore, the filter design procedures are presented in the context under specified filter performance. Finally, to verify the proposed design method, an example of self‐packaged TM‐BPF at 6 GHz with a good lower stopband and a wide upper rejection band is designed, fabricated, and measured. The measured results are in good agreement with simulated ones.

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A stripline hybrid dual‐capacitively loaded (DCL) substrate integrated waveguide (SIW) resonator is proposed and analyzed in this letter. First, the fundamental mode (TE101) and two higher order modes (TE102 and TE201) are shifted lower through the capacitive perturbation effect. Extra Striplines are then integrated with the proposed DCL triple‐mode resonator to generate transmission zeros both below and above the passband. Subsequently, the proposed stripline hybrid DCL SIW resonator is used to design an example fourth‐order filter with three transmission zeros. A step‐by‐step design guideline is then summarized under specified filter performance. Finally, to verify the proposed design method, an example fourth‐order bandpass filter at 5.5 GHz with an improved lower rejection band is designed, fabricated, and measured. The measured results indicate that this filter has the advantages of compact size, good selectivity, and easy three‐dimensional integration.

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