Monolithically-Integrated Coaxial Resonator-Based Bandstop Filters Enabled by SLA 3D Printing

This article reports on a new class of compact, lightweight, monolithically-integrated coaxial cavity resonator-based bandstop filters (BSFs) using stereolithography apparatus (SLA) 3D printing. The BSF concept is based on 3D printed coaxial cavity resonators that are directly coupled by an air-filled coaxial transmission line. Size compactness is achieved by: i) using low-profile sub-wavelength coaxial cavity resonators and by ii) monolithic SLA 3D printing that eliminates the need for assembly screws. For proof of validation purposes, a second-order BSF was designed, manufactured, and measured. Measurement results exhibit a center frequency (fc) of 4.5 GHz, stopband rejection of 48 dB, 10 dB fractional bandwidth (FBW) of 1.7%, and an effective quality factor Q(eff) of 760.