Compact Self-Supportive Filters Suitable for Additive Manufacturing

An irregular-hexagonal resonator geometry is proposed for additively manufactured microwave filters. This geometry allows closely packed resonators to form very compact filters of various topologies fulfilling transfer functions with transmission zeros (TZs). It also minimizes the overhangs and allows vertical printing along the direction of the input–output ports, without any internal support structure and with a much-reduced profile. The characteristics of the resonator and the tradeoff between compactness and quality factor have been analyzed. Three bandpass filters have been demonstrated. Two of them are designed with nonresonating node topologies with fractional bandwidths of 5% and 1%, respectively, using the step-tuning technique. All three filters are fabricated using selective laser melting (SLM) technique. The performance of the fabricated filters is compared with the EM simulation. Very good agreement has been achieved for all three filters. The effectiveness of tuning has also been demonstrated. The resonator structure has offered high printability in the manufacturing and high level of modularity and flexibility in the design.