# Influence of Dielectric Plate Parameters on the Reflection Coefficient of a Planar Aperture Antenna
## 1 Introduction
The aperture antenna is covered with a dielectric plate, and the changing of two parameters such as the thickness and permittivity of the radome has shown that it is possible to obtain rather good broadband admittance matching. Similar research was carried out by the authors in [11], but it involved an aperture antenna fed by a waveguide with a circular cross-section mounted on a grounded plane. Moreover, the opening of the antenna is covered with a dielectric plate, and the research results showed that by changing only two parameters of the dielectric, it is possible to influence the reduction in the reflection coefficient of the antenna in question. Software for numerical calculation of the reflection coefficient \(S_{11}\) of an aperture antenna fed by a circular waveguide covered with a dielectric plate was Ansys HFSS (three-dimensional electromagnetic (EM) simulation software for the design and simulation of HF electronic element-antennas and antenna arrays). The theoretical and mathematical basis of the aforementioned software for solving problems in electromagnetism is the finite element method. This article is a continuation of the research aimed at improving impedance matching of the aperture antenna and a detailed analysis of the structural and electromagnetic parameters of the dielectric plate placed on the antenna, [10; 11; 12]. References [10; 11; 12] analyze the influence of only two parameters (thickness and permittivity) of the dielectric on the admittance or reflection coefficient, whereas this article analyzes the influence of all parameters of the dielectric plate (thickness of the material d in mm, density of the dielectric \(\rho\) in kg\(\cdot\)m\({}^{-3}\), relative permittivity \(\varepsilon_{\mathrm{r}}\), conductivity of the dielectric \(\sigma\) in S/m, losses in the dielectric tan \(\delta\) and tan \(\delta_{\mathrm{\mu}}\), and relative permeability of the material \(\upmu_{\mathrm{r}}\)), and finally, simulation is validated with measured values. The aim of the article is to achieve the lowest possible reflection coefficient of the circular aperture antenna in order to accomplish the best impedance matching of the antenna itself. Further study [13] considers polyurethane foams as dielectric materials in the construction of radomes. The study includes the following EM parameters of radomes: the relative dielectric constant and tangent loss at the frequencies ranging between 1 and 10 GHz. The authors in [14] deal with the influence of water on the electrical conductivity and dielectric parameters of a microwave absorber, clarifying the difference between losses due to electrical conductivity and dielectric losses in the dielectric material (polarization). The first section provides an overview of existing research on the performance of the dielectric radome, its parameters, and its influence on the overall performance of the antennas on which it is mounted. In the second section, a theoretical description of the incident wave on a dielectric single-layer material is given with analytical equations of the material parameters of the dielectric plate. Furthermore, all structural-geometric and electromagnetic (EM) parameters of the dielectric single-layer plate are presented, which are processed in the article by both simulation and measurement. Section 3 presents in detail the simulation results that describe the influence of the specified parameters of the dielectric plate on the aperture reflection coefficients of the antenna where the dielectric plate is located. Section 4 contains the measurement results of the reflection coefficients that are compared with the simulation results. The last section provides a detailed explanation of the results obtained for the influence of the dielectric plate parameters on the reflection coefficients of the antenna aperture with the dielectric plate. In this article, the reflection coefficient S\({}_{11}\) of the TE\({}_{11}\) mode aperture antenna fed by a circular waveguide covered with dielectric is simulated and measured.