Design, Manufacturing, and Characterization of Conical Blackbody Targets With Optimized Profile

This paper describes the design, manufacturing, and characterization of conical blackbody targets to be integrated in millimeter and submillimeter wave radiometers. In particular, we present the electromagnetic properties of the binding material Stycast 2850FT, which is suitable at cryogenic temperatures, with microwave absorbing fillers between 100 and 420 GHz. On the basis of these extensive measurements we have determined the parameters of a mixing formula, which can be applied to calculate the composite properties with an arbitrary concentration of the filling material. Furthermore, we demonstrate that significant improvements of the electromagnetic properties of a calibration target can be achieved with an optimization of the cone profile. We compare the coherent backscattering S11 of conical targets with a common linear and an exponential-shaped cone. Numerical calculations have been carried out showing a reduced reflectivity of targets with an exponential cone profile. The coherent backscattering S11 of two target prototypes has been measured in different frequency bands between 105 and 410 GHz experimentally validating the simulations.