125 GHz frequency doubler using a waveguide cavity produced by stereolithography

This letter reports on the first Schottky diode frequency doubler with a split-block waveguide structure fabricated by a high-precision stereolithography (SLA) printing process. The printed polymer waveguide parts were plated with copper and a thin protective layer of gold. The surface roughness of the printed waveguide parts has been characterized and the critical dimensions measured, revealing good printing quality as well as a dimensional accuracy that meets the tight tolerance requirements for sub-terahertz active devices. The 62.5 GHz to 125 GHz frequency doubler circuit comprises a 20 m thick GaAs Schottky diode monolithic microwave integrated circuit (MMIC) in the waveguide. The measured doubler provides a maximum output power of 33 mW at 126 GHz for input power of 100 mW. The peak conversion efficiency was about 32% at input powers from 80 to 110 mW. This doubler performance is compared with and found to be nearly identical to the same MMIC housed in a CNC-machined metal package. This work demonstrates the capability of high-precision SLA techniques for producing sub-terahertz waveguide components.