# Multi-Band Unmanned Aerial Vehicle Antenna for Integrated 5G and GNSS Connectivity
## 2 Dual-Port Inverted T-Shaped MIMO Antenna and Analysis
\begin{bmatrix}1&0\\ \frac{1}{Z_{i}}&1\end{bmatrix} = \begin{bmatrix}1&0\\ j0.0054&1\end{bmatrix}  \tag{3}\]  
where \(Z_{i}=-jZ_{0}\text{cot}\,\theta\). Then, the defective ground structure was evaluated by using L and C values:  
\[T_{\text{C1}}= \begin{bmatrix}A&B\\ C&D\end{bmatrix} = \begin{bmatrix}1&Z_{\text{s}}\\ 0&1\end{bmatrix} = \begin{bmatrix}1&j0.00223\\ 0&1\end{bmatrix}  \tag{4}\]  
where \(Z_{\text{s}}=\frac{1}{j\omega L}+j\omega C\), \(\omega=2\pi f\), and \(f\) is the operating frequency. The total transfer matrix (T\({}_{\text{total}}\)) is as follows:  
\[T_{total1}=T_{A1}*T_{B1}*T_{C1}*T_{B1}*T_{A1} \tag{5}\]  
\[T_{total1}= \begin{bmatrix}A&B\\ C&D\end{bmatrix} = \begin{bmatrix}0.298&j40.73\\ j0.0219&0.311\end{bmatrix}  \tag{6}\]  
The scattering parameter of the reflection coefficient is calculated using Equation (7):  
\[S_{11}=\frac{A+\frac{B}{Z_{imp}}-CZ_{imp}-D}{A+\frac{B}{Z_{imp}}+CZ_{imp}+D} \tag{7}\]  
\[S_{11}=0.173-j0.048 \tag{8}\]  
\[|S_{11}|=-14.91\text{ dB} \tag{9}\]  
By using the ABCD parameters, the reflection coefficient (S\({}_{11}\)) was derived. The derived S\({}_{11}\) was \(-14.91\) dB at 1.3 GHz, which was closest to the simulated value of \(-16.835\) dB. Similarly, the reflection coefficient for the 5G band was derived by using the ABCD matrix as follows:  
\[T_{A2}= \begin{bmatrix}A&B\\ C&D\end{bmatrix} = \begin{bmatrix}\cos\theta&jZ_{imp}\sin\theta\\ j\sin\frac{\theta}{Z_{imp}}&\cos\theta\end{bmatrix} = \begin{bmatrix}-0.580&j4 0.7\\ j0.0162&-0.580\end{bmatrix}  \tag{10}\]  
The ABCD matrix for the open circuit (T\({}_{B}\)) is as follows:  
\[T_{B2}= \begin{bmatrix}A&B\\ C&D\end{bmatrix} = \begin{bmatrix}1&0\\ \frac{1}{Z_{a}}&1\end{bmatrix} = \begin{bmatrix}1&0\\ -j0.0032&1\end{bmatrix}  \tag{11}\]  
Then, the defective ground structure was evaluated by using the L and C values:  
\[T_{\text{C2}}= \begin{bmatrix}A&B\\ C&D\end{bmatrix} = \begin{bmatrix}1&Z_{\text{s}}\\ 0&1\end{bmatrix} = \begin{bmatrix}1&j0.0004\\ 0&1\end{bmatrix}  \tag{12}\]  
The total transfer matrix (T\({}_{\text{total}}\)) is as follows:\[T_{total2}=T_{A2}*T_{B2}*T_{c2}*T_{B2}*T_{A2} \tag{13}\]  
\[T_{total2}= \begin{bmatrix}A&B\\ C&D\end{bmatrix} = \begin{bmatrix}-0.476&-j36.23\\ -j0.0198&-0.404\end{bmatrix}  \tag{14}\]  
The scattering parameter of the reflection coefficient (S\({}_{11}\)) is calculated as follows:  
\[S_{11}=0.1257-j0.0225 \tag{15}\]  
\[|S_{11}|=-17.87\mathrm{dB} \tag{16}\]  
By using the ABCD parameters, the reflection coefficient (S\({}_{11}\)) was derived. The derived S\({}_{11}\) was \(-17.87\) dB at 4.58 GHz, which was closest to the simulated value of \(-25.86\) dB. Figure 5 represents the graph of the reflection coefficient (S\({}_{11}\)/S\({}_{22}\)), isolation loss (S\({}_{12}\)), and insertion loss (S\({}_{21}\)) for the proposed 1 \(\times\) 2 MIMO antenna design. From the graph, it is understood that there is no mutual coupling between the patches since there is no overlap between the S\({}_{11}\)/S\({}_{22}\) and the S\({}_{21}\) and S\({}_{12}\) graphs. An additional structure called a frequency selective surface was added to the MIMO antenna to further enhance the gain and directivity. A frequency selective surface (FSS) refers to a thin, repeating surface, such as a microwave oven screen, designed to interact with electromagnetic fields by selectively reflecting, transmitting, or absorbing them based on frequency. FSS structures typically exhibit two- or three-dimensional periodic patterns, consisting of a metal sheet with an infinite array of metal apertures or patches printed on a dielectric substrate. These surfaces act as spatial filters, wherein incoming electromagnetic waves are either partially or entirely reflected or transmitted over specific frequency ranges, depending on the design of the array elements. FSS are categorized into four types based on their filtering characteristics: low-pass, high-pass, band-stop, and band-pass filters.