LIGA fabrication of folded waveguide circuits

Economical, compact, high-frequency (100 GHz, wideband (20 GHz) power amplifiers providing high-power (100 W) are needed for emerging space applications. A major challenge in realizing high frequency power amplifiers is the fabrication of the folded waveguide (FWG) vacuum power booster. LIGA fabrication offers the potential of significant cost savings through batch fabrication of folded waveguide circuits. The completed FWG will be a solid piece of copper, providing efficient cooling needed for a high power RF circuit. Additionally, with the LIGA technique, one has the unique ability to fabricate, as one unit, both the circuit and the waveguide transition with the required dimensional tolerance, thus eliminating a major source of RF mismatch. The Deep X-ray Lithography (DXRL) exposure and polymethylmethacrylate (PMMA) development parameters have been optimized for the pattern layout and the PMMA thickness. The aspect ratio of the developed PMMA is 6:1, and the structures show good sidewall verticality and surface roughness. Following development of the PMMA, the circuits have been electroformed with copper, and examples of the circuits are shown.