Numerical synthesis method for designing a shaped dual reflector feed system

Manufacturing of submillimetre-wave-region holograms for compact antenna test ranges can be facilitated by using a shaped illumination for the holograms. The illumination is realised with a dual-reflector feed system (DRFS) consisting of two shaped offset hyperboloids. A simple ray-tracing-based synthesis procedure was developed for designing such a feed system. In the synthesis procedure, the reflector surfaces are approximated by locally planar sections. The electromagnetic fields are approximated with infinitely small rays and they are assumed to represent the local planewave phase and amplitude. These approximations in the ray tracing approach allow simple numerical solutions for the synthesis problem. The developed synthesis procedure was used to design a DRFS operating at 310 GHz. The effect of the number of rays used in the synthesis on the accuracy of the reflector surfaces was also studied. The DRFS beam was simulated using physical optics and physical theory of diffraction, at the frequency of 310 GHz with the commercial reflector antenna analysis software GRASP8W. The simulated beam corresponds well with the desired hologram illumination.