# Influence of Dielectric Plate Parameters on the Reflection Coefficient of a Planar Aperture Antenna
## 5 Discussion  
The radome placed on the antenna serves several purposes. It protects the antenna and constituent parts from external disturbances (e.g., snow, rain, wind, etc. ), but research has  
Figure 13: (**a**) Measurement of the S\({}_{11}\) coefficient of the aperture antenna fed by a circular waveguide (covered with dielectric material) with an N9914A FieldFox Handheld RF Analyzer (6.5 GHz); (**b**) side view; (**c**) aperture antenna without radome; (**d**) space inside the waveguide. shown that the exact choice of the material covering the antenna can significantly affect its properties and performance. The investigated materials that can constitute certain radomes are polycarbonate, Teflon, and polystyrene-dielectrics, because they are able to maintain good antenna performance and a satisfactory reflection coefficient, i.e., materials with the lowest possible dielectric constant and tangent loss. This article analyzes the influence of all parameters (whether geometric or electromagnetic) on the change in the reflection coefficient at the aperture of the antenna covered with a dielectric. It can be concluded that by placing a dielectric plate on the antenna, the reduction in the reflection coefficient S\({}_{11}\) can be significantly affected, and with the proper selection of all dielectric parameters, this coefficient value can be brought to the minimum value. Figure 14 clearly shows the situations in which no dielectric plate is placed on the antenna and in which a dielectric plate with the best parameter values achieved (d = 11 mm, \(\varepsilon_{\mathrm{r}}\) = 2.5, \(\mu_{\mathrm{r}}\) = 1, \(\rho\) = 1200 kg\(\cdot\)m\({}^{-3}\), \(\sigma\) = 0 S/m, \(\tan\)\(\delta\) = 0.09, \(\tan\)\(\delta_{\mu}\) = 0) is placed on the antenna. However, a systematic analysis of the known dielectric parameters (geometric and electromagnetic) and their influence on the reflection coefficient and, thus, on impedance matching, as well as the choice of the frequency range of the antenna itself, was carried out as a part of this study. The present article is intended as a detailed extension of previous studies on the influence of just two parameters (thickness and permittivity) on impedance matching or the reflection coefficient [10; 12]. This article analyzes the influence of all parameters of the dielectric plate. The geometrical parameters taken in this analysis are the thickness d and width/length h\({}_{1}\)/h\({}_{2}\) of the dielectric plate. The electromagnetic parameters used in this analysis are the real and the imaginary part of permittivity (\(\varepsilon_{\mathrm{r}}\), tan \(\delta\)) and electrical conductivity of the dielectric plate (\(\sigma\)). Simulation calculation and analysis included other structural and electromagnetic parameters of the dielectric plate  
Figure 14: Simulated reflection coefficient S\({}_{11}\) for an aperture antenna with a dielectric plate of thickness d = 11 mm and without dielectric plate (d = 0 mm). (density of the dielectric material, relative permeability, and magnetic loss tangent (\(\rho\), \(\upmu_{r}\), and \(\tan\delta_{\upmu}\))), but the results showed that in the range of real values of dielectric parameters for the materials used for the dielectric plate, those three parameters had no significant influence on the reflection coefficient. Finally, simulation is validated with measured values. The aim of the study was to achieve the lowest possible reflection coefficient of the circular aperture antenna in order to accomplish the best impedance matching of the antenna itself. The first part of the study involved simulation of the reflection coefficient of the antenna aperture fed by a circular waveguide using Ansys HFSS simulation software. The parameter analyzed, which significantly affects the performance of the antenna, is the thickness of the dielectric plate on the aperture. The thickness d ranges from 1 to 13 mm, and studies have shown that the best value of S\({}_{11}\) = \(-\)43.43 dB is obtained for d = 11 mm.