3-D printed filter based on helical resonators with variable width

This paper presents a helical resonator bandpass filter produced using a stereolighography (SLA) based 3-D printing technique. The filter is formed of four coupled helical resonators, and for each resonator the helix is fixed at both ends so that the resonator is less prone to vibration. The helix is designed to have variable width and this yields enhanced performance in terms of a higher unloaded quality factor and a spurious resonance at higher frequencies. Such a helix is ideally suited to 3-D printing which allows easy production of complex structures. The whole filter is printed from a resin, then plated with metal, and tested. The measured result has a good agreement with simulations.