Mechanically Machined Microwave Multi-Layer Antireflective Coating of a Dielectric

We present theoretical and experimental results on mechanically machined multilayer antireflective coating of a dielectric plate. The microwave ouptut window made of fluoroplast with the refractive index n = 1.41, was studied experimentally. Holes of two different diameters were drilled in a honeycomb pattern on the surface of the dielectric to different depths in such a way that two thin quarter-wave layers were formed. The effective dielectric permittivity of the obtained layers with cylindrical inhomogeneities was calculated by the Maxwell–Garnett method. The parameters of the layers were chosen according to the Chebyshev method. This allowed us to achieve a reflection coefficient of −30 dB in the frequency range 65–100 GHz. The experimental results were compared with the theoretical calculation and the numerical analysis performed via the multiple-reflection method.