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.