A Monolithic Vertical Integration Concept for Compact Coaxial-Resonator-Based Bandpass Filters Using Additive Manufacturing

This letter 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: 1) flexible cross couplings to be realized enabling highly selective transfer functions through transmission zero (TZ) generation and 2) 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 (IL) (<0.1 dB), high effective quality factors >1833, and wide spurious-free operation.