Design of a 3D-Printed Compact Coaxial Sleeve Bandpass Filter with High Harmonic Suppression Characteristic

This article proposes a miniaturized coaxial sleeve structure manufactured based on 3D printing technology for the first time. The resonant cavity consists of an inner column and a sleeve that is very close to each other. By reducing the distance between them, better harmonic suppression performance can be achieved without changing the volume. To verify these characteristics, a second-order single passband filter is designed, and the selectivity of the filter is improved by setting external coupling ports. The harmonic suppression multiple reaches 9.5 times and integrated printing is achieved by adding non-radiating slots. The 3D printing process can achieve the advantages of high precision and lightweight, ensuring good performance of the filter. Good agreements between the simulated results and the measured ones verify the feasibility of the proposed design method.