SLS-Printed E-Band Waveguides and the Impact of Surface Roughness

This work demonstrates the feasibility of selective laser sintering (SLS) as an additive manufacturing process for waveguide components up to the mm-Wave frequency range. Five E-band waveguides are fabricated employing a polyamide (PA) based SLS printing system and the slotted waveguide approach. The specimens are metallized involving a proprietery coating concept ending in an electroplated copper surface finish. A surface roughness analysis as well as an electrical analysis are conducted. The mean RMS-surface roughness of the specimens is measured as 21,9$\mu$m. The electrical measurements result in a reflection coefficient of better than -15 dB at 60 GHz to -12 dB at 90 GHz and an attenuation coefficient of less than 5 dB/m. Simulations are conducted to analyse the impact of surface roughness. In order to confirm the results, measurements and simulations are are also evaluated in X-band. The results suggest the use of the cummulative distribution function of the surface for reliable simulations. Where the physical surface roughness ecxeeds the skin depth, the skin depth can be used as a first estimation of the RMS sufrace roughness.