THz smooth-walled spline horn antennas: Design, manufacturing and measurements

We describe a versatile and cost-efficient method for producing smooth-walled spline horn antennas for applications in THz radiometry. Specifically, the development of four different horns for radiometer receiver applications at frequencies 120, 183, 340 and 874 GHz is presented. General methods for efficient optimization of the spline profiles have been developed which enable the horn designs to be tailored to each application. All four designs display high Gaussicity (typically ~98%). Manufacturing methods based on numerical milling in splitblocks, lathing and drilling have been tested and compared. Milled splitblock horns with integrated receiver circuits (Shottky mixers in this case) allow for lower losses in the receiver system at the expense of higher cross-polarization levels. The radiation pattern of three designs at 183, 340 and 874 GHz have been measured using planar and rotational scanners.