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.