Band-Pass Filters through Unmetallized 3D Printed Dielectric Waveguide Inserts

We present a novel approach to realizing band-pass filters by inserting unmetallized 3D printed dielectric inserts into off-the-shelf waveguide. The insert is synthesized by commensurate line theory by either using air-filled lines with dielectric inverters or dielectric-filled lines with air gap inverters. In both cases, good first-iteration accuracy from a quasi- analytical calculation of inverter and line dimensions is achieved, although the low dielectric constant of the available materials constrains the design to wide pass-bands. Four examples are designed and printed in polyamide 12 and polypropylene for WR90 waveguide, with responses of 20% relative bandwidth centered at 10 GHz achieving best-case insertion loss of 0.25 dB using air-filled waveguide and polypropylene inverters.