# A Review of Unmanned Aerial Vehicle Based Antenna and Propagation Measurements
## 3 UAV-Based Propagation Measurements
### Accuracy Analysis of UAV-Based Antenna Measurement  
The accuracy of the UAV-based antenna measurements mainly depends on the accuracy of the RF equipment mounted on the UAV, the amount of vibration experienced by the UAV, the accuracy of the GPS positioning, and the external environmental conditions. To understand how these aspects affect the measurements, Table 4 describes the variations in the radiation patterns measured by the UAV. All these measurements were performed by a UAV to characterize an antenna installed outdoors. After characterizing the antenna in terms of the radiation pattern, the same antenna was measured in anechoic chambers, and in some cases, it was simulated using commercially available EM solvers. As described in Table 4, it can be understood that due to the UAV vibrations, external environmental conditions, and drifting in the UAV positions, a maximum error of 1 dB in the peak amplitude is noticed. These results indicate that UAV measurements are an accurate and a reliable solution for characterizing an antenna. In UAV-based antenna measurements, the radiation patterns of the antenna in either the azimuth or elevation plane were obtained by following a predefined trajectory. For the UAV to follow this predefined trajectory, the UAV path planning is achieved through software tools such as QGroundControl v1.3.8 [103]. The accuracy with which the GPS follows the defined waypoints depends on the accuracy of the GPS used on the UAV. Based on the frequency of operation, GPS systems such as differential RTK (D-RTK), RTK, \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Reference**} & \multirow{2}{*}{**Frequency (GHz)**} & **Difference Between UAV** & \multirow{2}{*}{
\begin{tabular}{c} **Difference Between UAV** \\ **and Anechoic Chamber** \\ **Measurements** \\ \end{tabular} } \\  & & & **Measurements** & \\ \hline
[1] & 0.75 & NA & 0.5 dB in peak amplitude \\
[4] & 0.47 to 0.7 & NA & 0.6 to 1 dB in peak \\
[7] & 0.7 to 0.8 & NA & 0.5 to 1 dB in peak \\
[27] & 14.5 & 0.38 dB in peak amplitude & NA \\
[42] & 4.65 & Widening in radiation & NA \\
[50] & 0.175 & NA & \textless{}1 dB in peak amplitude \\
[98] & 0.05 to 0.35 & NA & 0.5 to 1 dB in peak amplitude \\
[99] & 8 to 12 & 0.5 dB in peak amplitude, & NA \\  & & 0.06\({}^{\circ}\) in HPBW & NA \\
[100] & 0.05 to 0.32 & NA & \textless{}0.1 dB in peak amplitude \\  & & & and 1 dB in SLL \\
[101] & 44 & 1 dB in peak amplitude & NA \\
[102] & 4 to 6 & 3 dB in peak amplitude & NA \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Accuracy of UAV-based antenna measurements. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Reference** & **Antenna** & **Frequency Range (GHz)** & **Radiation Pattern** \\ \hline
[21] & Micro–Strip Patch & 1.8–2.7 & Directional \\
[87] & Micro–Strip Patch & 2.4–5.2 & Directional \\
[93] & Log–periodic meandered & 0.85–2.2 & Directional \\  & dipole array & & \\
[94] & Vivaldi & 1.5–4.5 & Directional \\
[95] & Horn & 7.5–18 & Directional \\
[90] & Dipole & 0.55–1.6 & Omnidirectional \\
[96] & Surface Wave & 6.1–18 & Directional \\
[91] & Helix & 0.6–1.1 & Omnidirectional \\
[97] & Quasi–Yagi & 23–28.5 & Directional \\
[92] & Half–bowtie antenna & 4.1–5.6 & Directional \\ \hline \hline \end{tabular}
\end{table} 
Table 3: State–of–the–art antennas for UAV applications. differential GNSS, and real-time differential GPS are used. These high-precision systems are particularly used for UAV measurement applications, which can provide centimeter and sub-meter accuracy. Based on the UAV-based antenna measurements conducted in [27], it is evident that a total deviation of 0.38 dB between the UAV-based measurements and the measurements in the anechoic chamber is observed. Out of the 0.38 dB variation in the peak amplitude of the radiation patterns, 0.36 dB is due to the external environmental conditions; small inaccuracies in D-RTK positioning result in a 0.01 dB variation, and variations in RF component behavior due to outdoor temperature result in a 0.02 dB variation.