Design of a hyperbolic microwave metallic lens

Due to problems caused by multiple reflections in the cavity walls of the EBT fusion research device, the use of a horn becomes important for the directivity of waves in the millimetric range. An ordinary dielectric lens cannot be used because of plasma–wall interactions. Microwave metallic lenses, designed to focus the energy into a plane wave, can improve the directivity considerably. By implementing a 70‐GHz standard‐gain horn with a delay‐type hyperbolic lens, which consists of a solid metallic disk with a number of equal size small holes, a gain of 15 dB over the no lens case was realized.