Micro-machined integrated waveguide transformers in thz pickett-potter feedhorn blocks

We present laboratory measurements 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. Compared to previous transformer segments machined into separate blocks or machined into split-block segments, we ensure axial alignment along the waveguide segments at the cost of rounding the edges of the rectangular waveguide. This architecture was fabricated by direct metal micro-machining, which offers significant advantages over competing techniques in complexity, timescale, and cost of manufacturing. All machining passes during manufacture can be made from the front of the block including the final waveguide segment. We compared simulations of the waveguide circuit performance using multiple electromagnetic software packages to finalize the dimensions of the optimized transformer module. A single pixel feedhorn-transformer module was manufactured on a 3-axis CNC milling machine. We tested integrated feedhorn-transformer modules using waveguide-fed hot electron bolometer mixers designed and fabricated at the Jet Propulsion Laboratory using a liquid helium-cooled cryostat. Beam 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 laboratory beam pattern.