Development of a corrugated horn at 2-THz band for a hot electron bolometer mixer

We are developing a waveguide-type hot electron bolometer mixer (HEBM) at 2-THz band for high-speed wireless communications (Beyond 5G) or atmospheric/astronomical observations. We are developing an HEBM with a diagonal horn and are also developing an HEBM with a corrugated horn at 2-THz band to improve the beam pattern performance. A corrugated horn has a good axisymmetric beam and polarization characteristics over wide band, although machining of a small corrugation structure is difficult. The width of the teeth was designed to be 15 mu m(sic)/20 mu m(sic) with a depth of 37.5 mu m. The corrugated horn consists of a 120 number of the teeth, 20 number of tapered teeth with a deepest depth of 75 mu m, and a circular to rectangular transition. The total length of the horn is 6.1 mm. A simulation result of the horn shows low reflection loss and low-side lobe level. We have fabricated a sample horn and confirmed the teeth structure were well machined by measuring with a non-destructive inspection using X-ray. The size of the teeth was measured using X-ray and a laser microscope.