Fivefold Helically Corrugated Waveguide for High-Power W-Band Gyro-Devices and Pulse Compression

The design, simulation, manufacture, and measurement of a {W} -band fivefold (5F) helically corrugated waveguide (HCW) is reported. The 5F HCW is based on the coupling of the traveling TE 31 and near cutoff TE 22 modes to create an operating eigenwave. The fabricated test structure has circular waveguide ports and features elliptical polarizer sections and broadband TE 11 to TE 31 mode converters on either side of the 5F HCW. The optimized mode converter design, based on a fourfold (4F) HCW, has a predicted power conversion efficiency greater than 90% from 89 to 102.5 GHz, and 96% peak efficiency at 94 GHz. The optimization of the 5F HCW geometry produced an eigenwave suitable for gyro-devices, but the optimization could equally well have been directed to applications such as pulse compression and microwave undulators. Analysis of simulated electric field profiles showed that the propagating power in the 5F HCW was increased by a factor of 6 over that in the 3F HCW at equivalent peak electric field strength. This is due to the larger diameter of the waveguide. Test structures were manufactured through a combination of precision machining of a sacrificial mandrel, copper growth by electroforming followed by removal of the aluminum mandrel by chemically etching. Measurements of the 5F HCW structure's dispersion showed excellent agreement with the prediction over the design range of 90-98 GHz.