Micromachined Integrated Waveguide Transformers in THz Pickett-Potter Feedhorn Blocks

We present the design, fabrication technique, and performance of a circular-to-rectangular waveguide transformer integrated into a 1.9 THz Pickett-Potter feedhorn detector block. This design is applicable for instruments where circularly symmetric feedhorns are required to mate with rectangular waveguide-fed receiver devices that house the detector chip. The transformer was fabricated by direct metal micromachining, which offers significant advantages in reducing the complexity, timescale, and cost of manufacturing over competing techniques, such as transformer segments machined into separate blocks or machined into split-block segments. We simulate the tradeoff between the fabrication technique and the cost of rounding the edges of the rear rectangular waveguide. Simulations of the transformer circuitry using multiple electromagnetic software packages were used to finalize the dimensions of the optimized transformer. A single pixel feedhorn-transf ormer module was manufactured on a three-axis milling machine to test the feasibility of the design and manufacturing technique. We tested the performance of the integrated feedhorn-transformer modules using waveguide-fed hot electron bolometer mixers designed and fabricated at the Jet Propulsion Laboratory. Radiation patterns of the Pickett-Potter modules were measured using a high-power 1.9 THz multiplication chain as the source. We find good agreement between the simulated and measured beam pattern.