Surface roughness impact on the performance of the 3D metal printed waveguide coupler at millimeterwave band

This paper presents the impact of surface roughness on the performance of a three –dimensional (3D) metal printed waveguide coupler designed at 28 GHz. The surface roughness is a significant factor that may affect 3D printed structures and post processing may be needed. It may degrade the performance of the printed devices in term of the reflection coefficient and increases the insertion loss. Thus, this work analyses the surface roughness impact on the 3D metal printed coupler designed at 28 GHz. The hybrid coupler is a waveguide-based structure with coupled resonators and the coupling is controlled by tuning the iris dimensions. The measurement is done without any post processing procedure to ensure the validation of the printed coupler with simulation results. The surface roughness measurement is performed with six tested areas of coupler structure using advanced 3D optical microscope. Then, the measured surface roughness values are included in CST software to re-simulate and compare with the original and measured results. The analysis shows that the surface roughness has a moderate influence on the reflection coefficient with 7 dB loss and 0.7 dB increased in insertion loss at 28 GHz.