Design of Miniaturized Ceramic Waveguide Filter Utilizing a Three-Blind-Hole Structure

In the realm of high-performance filter research, the challenge of miniaturizing filters has persistently posed difficulties. Therefore, this study introduces a compact ceramic waveguide filter based on a three-blind-hole coupling structure. By employing the three-blind-hole coupling configuration, both inductive and capacitive couplings are realized, leading to the emergence of two transmission zeros within the cascaded quadrupling (CQ) framework. This, in turn, enhances the frequency selectivity of the ceramic filter and effectively reduces its physical footprint. Building upon this foundation, a six-cavity ceramic waveguide filter tailored for 5G base stations is designed. A comprehensive analysis of the influence of three-blind-hole depths and inter-hole spacing on coupling coefficients is conducted, and the corresponding variations are summarized. Through meticulous simulation validation, the designed filter exhibits the following performance metrics: a center frequency of 3.5 GHz, operational bandwidth of 200 MHz, insertion loss ≤ 1.2 dB, return loss 2≥ 20 dB, near-stopband suppression 2≥ 25 dB, and far-stopband suppression 2≥ 51 dB.