# Smart Antenna for Application in UAVs
## 3 P-ESPAR Antenna Study
### P-ESPAR Antenna Configuration  
The developed P-ESPAR antenna consists of an aggregate of three elements, the middle element being the active element, and the remaining parasitic elements. The three elements have the same dimensions. The antenna has a resonance frequency of 1.33 GHz.  
The choice of substrate was a choice conditioned by economic reasons. Initially, the chosen substrate was the RT Duroid 5870, but given its high cost, the prototype of the antenna was constructed with a substrate composed of two plates of FR-4 and an air layer of a thickness that allows to obtain a structure with the same constant (\(\epsilon_{\mathrm{r}}\)), its homogeneity, the tangent of the loss angle (tan8), and the thickness (h). The equivalent model is accepted to have the same characteristics of RT DUROID 5870, but with a different thickness. For this reason, the patches were resized, the antenna simulation work repeated, and, therefore, other coupling diodes were chosen so that the antenna was perfectly adapted to the design requirements.  
The antenna was constructed to present the same dielectric constant equivalent of RT Duroid 5870, for which two FR-4 substrates with one layer of air were used between them to approximate the dielectric constant to the Duroid RT 5870 values. Table 2 shows the characteristics of the FR-4 substrate and the Duroid 5870 RT for antenna sizing.  
After choosing the substrate, the dimensions of the P-ESPAR antenna patch were calculated.  
Then, the values of these dimensions were optimized using a CST Microwave studio software optimization tool. Table 3 shows the values obtained from the sizing and subsequent optimization; it is also possible to observe the value obtained for the resonance frequency in Table 4.  
In Figures 4 and 5, it is possible to identify the calculated dimensions with their location on the P-ESPAR antenna.  
\begin{table}
\begin{tabular}{c c} \hline Frequency & 1.330 GHz \\ Gain & \textgreater{}3 dB \\ Bandwidth & \textgreater{}8 MHz \\ Coefficient of reflection \(\mid\!\!_In the following sections, we present the results of the previous section.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{3}{c}{**Two Layers of FR-4 with One Layer of Air**} \\ \hline \((f_{r})_{010}\) & 1.368 GHz \\ \((f_{rc})_{010}\) & 1.330 GHz \\ \hline \hline \end{tabular}
\end{table}
Table 4: Frequency of resonance.  
Figure 4: Structure and dimensions of the P-ESPAR antenna in the frontal perspective [15].  
Figure 5: Corss-section view of the P-ESPAR antenna.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{3}{c}{**FR-4**} \\ \hline \hline  & & **Dimension** & **Optimization** \\ \hline Patch width & W & 87.400 mm & 84.300 mm \\ Patch length & \(L_{\text{P}}\) & 71.760 mm & 65.600 mm \\ Antenna length & \(L_{\text{ant}}\) & 274.900 mm & 274.900 mm \\ Transmission line width & \(W_{0}\) & 3.500 mm & 4.500 mm \\ Substrate thickness & H & 1.575 mm & 1.575 mm \\ Ground thickness & h\({}_{\text{g}}\) & 0.019 mm & 0.019 mm \\ Air layer thickness & h\({}_{\text{ar}}\) & 1.090 mm & 1.090 mm \\ Total thickness & h\({}_{\text{total}}\) & 4.240 mm & 4.240 mm \\ Diode length & G\({}_{\text{d}}\) & 3.000 mm & 3.000 mm \\ Position of mutual coupling of the diode & O & 30.000 mm & 30.000 mm \\ Insert feed point location & \(y_{0}\) & 22.842 mm & 20.000 mm \\ Resonance resistance & \(R_{in}(y=0)\) & 105.403 \(\Omega\) & 105.403 \(\Omega\) \\ Input resistance for insert feed & \(R_{in}(y=y_{0})\) & 50.000 \(\Omega\) & 50.000 \(\Omega\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Dimensions of the antenna with two substrate FR-4 plates and one layer of air.