Micromachining and Characterisation of Folded Waveguide Structure at 0.22THz

The demand of high-speed wireless communication has increased, which need the data rate to be in the order of Terabyte per second (Tbps) in the near future. Terahertz (THz) band communication is a key wireless communication technology to satisfy this future demand. This would also reduce the spectrum scarcity and capacity limitation of current wireless systems. Microfabricated Folded Waveguide TWTs are the potential compact sources of wide band and high-power terahertz radiation. This study primarily focuses on machining technology for THz waveguide components requiring ultra-high precision micromachining. Rectangular waveguides, especially Folded Waveguides (FW), are even more difficult to manufacture using conventional machining techniques due to their small size and very tight tolerances. The criticalities in micromachining of FW for 0.22 THz have been addressed in this article. Half hard free cutting Brass IS 319-H-2 was used as a work material due to its electrical and mechanical properties. Waveguide size of 0.852 x 0.12 mm was machined within +/- 3-5 mu m linear tolerances, surface roughness in the order of 45 nm R-a, and flatness less than half of wavelength (< lambda/2). The split top and bottom blocks of the folded waveguide were aligned by dowel pins which matched within a tolerance of +/- 5 mu m. The perpendicularity and parallelism were maintained within 5 mu m tolerance. This work explored and established the application of micromilling as reasonably suitable for the THz waveguides followed by ultrasonic cleaning as deburring. It also investigated the measured folded waveguide losses which were close to simulated values.