Design and implementation of evanescent mode waveguide filters using dielectrics and additive manufacturing techniques

In this contribution, we describe the design of bandpass filters using evanescent mode waveguides and dielectric resonators implemented with additive manufacturing techniques. Two C-band Chebyshev evanescent mode waveguide filters of order five have been designed using a low cost commercial dielectric material (ABSplus), widely used by Fused Deposition Modeling (FDM) 3D printers. The housings of the filters have been manufactured using traditional computer numerical control (CNC) machining techniques. Practical manufacturing considerations are also discussed, including the integration of dielectric and metallic parts. We first discuss two breadboards using two different resonator geometries. We then demonstrate how different transfer functions can be easily implemented by changing the 3D printed parts in the same metallic housing. Breadboards show fractional bandwidths between 3% and 4.6% with return losses better than RL=18 dB, and spurious free ranges of SFR=1 GHz. Insertion losses are better than IL=4.3 dB. Even though dielectric losses from the plastic material are shown to be high, the measured results are quite satisfactory, thereby clearly showing that this strategy maybe useful for the fast production of low cost microwave filters implementing complex geometries.