A monolithic vertical integration concept for compact coaxial-resonator-based bandpass filters using additive manufacturing

This paper reports on a compact, low-cost and low-loss monolithic integration concept for additively-manufactured coaxial-resonator-based bandpass filters (BPFs). Size compactness and low weight are achieved by vertically-stacking capacitively-loaded coaxial resonators and by monolithic integration that eliminates the need for assembly screws or fixtures. Furthermore, the proposed vertical integration concept allows for: i) flexible cross couplings to be realized enabling highly-selective transfer functions through transmission zero (TZ) generation and ii) for fairly complex geometries to be manufactured using low-cost stereolithography apparatus (SLA). For proof-of-concept demonstration purposes, a two-pole BPF with fractional bandwidth (FBW) of 8.5% and a three-pole/one-TZ BPF with FBW 6.2% at 3.8 GHz were designed, SLA-manufactured and measured. They exhibited low-levels of insertion loss ( 1,833 and wide spurious-free operation