# Measurement of Dielectric Properties of Thin Materials for Radomes Using Waveguide Cavities
## 3 Results
### Measurement Factors  
Despite these positive results, there are some factors that require consideration when following this type of measurement method. A major factor is the room temperature and its impact on the resonant cavity. Fluctuations in temperature can affect the data obtained through the network analyzer. This is especially observable if measurements are conducted on particularly warm days or performed over multiple days without remeasuring the foam-only case, which should be avoided wherever possible. Another possible solution is to perform measurements in a temperature-controlled environment to ensure that external factors are consistent. Measuring the cavity with only foam after each sample measurement is also another way to ensure that consistent measurements are performed. The network \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multirow{2}{*}{**Thickness**} & \multicolumn{3}{c}{**WR650 (Length = 105 mm)**} & \multicolumn{3}{c}{**WR137 (Length = 127 mm)**} \\  & & \multicolumn{3}{c}{**TE\({}_{101}\) (f\({}_{\text{c}}\) = 1.65 GHz)**} & \multicolumn{3}{c}{**TE\({}_{103}\) (f\({}_{\text{c}}\) = 5.575 GHz)**} \\ \cline{3-8}  & & **Permitity** & **Loss Tangent** & **Noise (K)** & **Permitity** & **Loss Tangent** & **Noise (K)** \\ \hline PTFE Fabric * & 0.00015 & 2.9 & 0.0009 & 0.0024 & 2.87 & 0.0044 & 0.0392 \\ Dynenenenene * & 0.0001 & 2.6 & 0.0019 & 0.0032 & 2.58 & 0.0135 & 0.0760 \\ N-Shell & 0.0003 & 1.4 & 0.0064 & 0.0236 & 1.4 & 0.0094 & 0.1169 \\
3-LL & 0.0003 & 2.09 & 0.0225 & 0.1012 & 1.98 & 0.0244 & 0.3608 \\
2-LL & 0.0002 & 1.87 & 0.0208 & 0.0590 & 1.85 & 0.0267 & 0.2545 \\ \hline \hline \end{tabular}
* Reference materials that have been used as radomes in previous projects.  
\end{table} 
Table 8: Summary of each material’s name, thickness, and calculated permittivity, loss tangent, and noise temperature for the five materials under test within WR650 and WR137 cavities for possible radome applications. analyzer settings are also important, as the number of points can impact the accuracy of the data obtained from the resonant peak plot. Increasing the power of the network analyzer can assist in producing a better signal-to-noise ratio and, hence, a higher Q-factor. This can be especially important for smaller shim irises and smaller waveguide cavities, which tend to provide, overall, more consistent and accurate results. The averaging of the signal can also be useful to ensure that an accurate peak is observed. Other factors that may have negative impacts also include foam distortion and mode degeneracy. Due to the tight fit required for the foam blocks within the waveguide cavity, inserting and removing them did result in slight indentations, which could have small effects on the consistency of the measurements. This removal and insertion process also caused some foam dust to be created. We found that this dust needed to be carefully cleaned from the waveguide mating surfaces each time the cavity was assembled to avoid lowering the Q-factors. Finally, mode degeneracy was observed during this experiment, specifically at some of the modes past the dominant mode. This degeneracy, or overlapping of modes, results in overlapping peaks, which can mean that accurate resonant peaks were not able to be identified at these other modes. Also, as this measurement technique utilizes Equations (6)-(11), it must be acknowledged that these are simplified equations. Therefore, some factors affecting permittivity and loss are not included. Further measurements are required at various higher frequencies to identify if these materials are suitable beyond the range covered here. Also, the measurement of these fabrics in different environments such as hot, cold, or wet, could also help to find any impacts radomes made of these materials may have on their antennas. With this further testing, we hope to create a database of materials that describes their features and performance at various frequencies and in multiple environments.