Compact 3D-Printed Bandpass Filters Using Coaxial and Dual-mode Ridged-Waveguide Resonators

This paper presents a new integration concept for 3D bandpass filters (BPFs) where coaxial resonators and dual-mode ridged waveguide resonators are combined within the same volume for miniaturization and RF performance enhancement. Size compactness is achieved by: i) two types of miniaturized resonators namely a coaxial and a dual-mode ridge waveguide resonator and ii) monolithic integration using stereolithography apparatus (SLA) 3D printing. A connectorized integration concept is also employed to facilitate the inter-connection with other SMA-probed RF devices. RF performance is enhanced through the combination of the two resonator types where the dual-mode resonator generates a transmission zero (TZ) close to the passband. A design process using coupled-resonator synthesis and eigenmode analysis is provided. The concept is experimentally validated at 4.9 GHz through the design, manufacturing, and testing of a BPF prototype with 3 dB fractional bandwidth of 7.3%, in-band insertion loss of 0.31 dB and Q
eff
of 1210.