Ultra‐miniaturization design of substrate‐integrated waveguide cavity trisection bandpass filter

The contribution of this work is to propose a novel trisection bandpass filter (BPF) using only one ultra‐miniature substrate‐integrated waveguide (SIW) cavity. The SIW cavity is composed of two substrate layers and a very thin prepreg layer for binding purpose. A circular patch is deployed on the cavity's middle metal layer and is evenly trisected into three identical pieces. Each piece is shorted to the cavity's bottom face by a blind via. The cavity together with the via‐shorted trisected patches form the trisection filter's resonators. This trisected‐patch‐loaded SIW cavity has the dominant‐mode resonance frequency much lower than that of the standard patch‐free SIW cavity. The down shift in the resonance frequency of the proposed resonator structure has effectively led to a significant circuit‐size reduction. When compared with a three‐pole BPF consisting of three standard patch‐free SIW cavities, the size reduction rate of our proposed BPF requiring only one SIW cavity is as high as 97.47%, which might be the highest record achieved so far. An experiment has been conducted to verify the proposed circuit design. Besides ultra‐circuit miniaturization, the measured upper stopband with the rejection of larger than 20 dB is as wide as 2.38 times the passband center frequency.