Surface roughness effects on additively manufactured aluminum Ka-band waveguide

Additive manufacturing of metal such as aluminum is an attractive alternative to rapidly manufacture high frequency waveguide components. However, the surfaces of the components can be rough, which can have an impact on electromagnetic propagation, such as additional loss and dispersion effects. To quantify the electromagnetic transmission performance, two pieces of WR-28 rectangular waveguides, three inches long, with two pairs of inductive irises were made using Direct Laser Sintering. The first piece was made from AlSi10Mg and the second is AL6061-RAM2. The AlSi10Mg was noticeably rougher, having a measured rms height variation of 1.8 mils, whereas the AL6061-RAM2 was 0.7 mils. The measured insertion loss at 32 GHz for the AL6061-RAM2 part was 1.1 dB versus 0.59 dB for the Al6061-RAM2 part. The simulated HFSS model without roughness shows at insertion loss of 0.36 dB.