Evanescent mode filters composed of dielectric parts built using 3D-printing methods

© 2021 IEEE.In this work, two different types of evanescent mode rectangular waveguides filters are proposed, designed and fabricated, using a hybrid manufacturing strategy. On the one hand, the evanescent waveguide filter section is filled with dielectric material made of ABSplus, commonly employed by 3D printers based on Fused Deposition Modeling (FDM). On the other hand, the metallic external structure of the filters has been built by means of standard machining computer numerical control (CNC) procedures. Some guidelines on how to properly combine the dielectric and metallic pieces are provided. As design examples, two different fifth order C-band Chebyshev bandpass filters have been designed and tested. The first filter is composed of a single ABSplus dielectric piece (¿r = 2.55) drilled with elliptical airholes, and then aligned in the metallic waveguide housing. The second filter is loaded with five elliptical dielectric post resonators distributed along the metallic evanescent waveguide section. In both cases, the return losses are higher than RL = 18 dB, the fractional bandwidth within the range 3%-4.6%, whereas the spurious free range is around 1 GHz. Due to the nowadays limitations of the quality of available dielectric materials for 3D-printers, the insertion losses of the filters are high within the passbands (around IL = 4.3 dB). Nevertheless, the overall performances are satisfactory, showing the promising usefulness of this kind of filters for low cost implementations, based on combining additive manufacturing techniques with standard CNC processes.