A Miniaturized SISL Bandpass Filter Based on Deep Hole Drilling Capacitor

ABSTRACT In this paper, a quasi‐lumped element‐based bandpass filter is implemented by substrate‐integrated suspended line (SISL) technology. To miniaturize the filter size, a deep hole drilling capacitor (DHDC) structure is proposed. The properties of DHDC are derived by parametric analysis and equivalent circuit analysis. Based on derived properties, a quasi‐lumped element bandpass filter using SISL technology is designed and fabricated. Experimental results demonstrate that the proposed bandpass filter achieves the center frequency f 0 ${{\boldsymbol{f}}}_{{\boldsymbol{0}}}$ of 1.48 GHz, with a fractional bandwidth of 50%. The minimum insertion loss within the passband is 0.96 dB, while the return loss exceeds 23.14 dB. The maximum out‐of‐band suppression is over −50 dB, and the filter size is only 0.172 λg × 0.062 λg.