## 2 Materials and Methods
### Antenna Design  
An antenna array with circular polarization and beam steering features is proposed in this article to reduce multipath fading and improve coverage and bandwidth. A circularly polarized wave reduces polarization mismatches and increases signal coverage by the reception antenna. Similarly, beam steering, as opposed to traditional antennas that radiate  
Figure 4: The 0 dB crossover’s (a) geometric layout and (b) proposed layout. Figure 5: Phase shifter (a) geometry and (b) proposed layout. in all directions, can broadcast signals just toward the device, reducing multipath signals. Many studies [62; 63; 64] have emphasized the several advantages of combining circular polarization and beam steering antennas in a variety of applications; nevertheless, it has not been adequately deployed and tested in underground mines. A single-element rectangular patch antenna with a 5.5 GHz frequency range was selected for the design and evaluation to enhance connectivity in underground mines. A single-element rectangular patch antenna is a type of antenna with a single radiating element. It is a cost-effective and simple yet effective design with significant advantages over more sophisticated antenna designs [65]. Because of its light weight and small size, this antenna has a wide range of uses in the mining industry. It may be utilized to communicate effectively between workers, equipment, and managers. These antennas can transmit and receive data, voice, and video signals, allowing for real-time communication between mine areas. In the mining industry, single-element antennas are also employed for navigation. They can be used to track the location of equipment and workers, allowing for more effective resource management and assuring safety. The 5.5 GHz frequency band, while relatively new and not as widely adopted, offers notable advantages compared to the more commonly utilized 2.4 GHz frequency range [66]. Because the 5.5 GHz frequency has a higher bandwidth, it can transmit more data at once. It also receives less interference from other devices, making it less susceptible to signal congestion and losses. Initially, a rectangular patch antenna with a frequency of 5.5 GHz was designed by computing the length and width measurements using Equations (7)-(9) [67; 68]. \[W=\frac{c}{2f_{0}\sqrt{\frac{\varepsilon_{R}+1}{2}}} \tag{7}\]  
\[\varepsilon_{eff}=\frac{\varepsilon_{R}+1}{2}+\frac{\varepsilon_{R}-1}{2} \left[\frac{1}{\sqrt{1+12\left(\frac{b}{W}\right)}}\right] \tag{8}\]  
\[L=\frac{c}{2f_{0}\sqrt{\varepsilon_{eff}}}-0.824h\left(\frac{\left(\varepsilon _{eff}+0.3\right)\left(\frac{W}{h}+0.264\right)}{\left(\varepsilon_{eff}-0.258 \right)\left(\frac{W}{h}+0.8\right)}\right) \tag{9}\]  
where \(W\) is the width of the patch, \(\varepsilon_{eff}\) is the effective permittivity, \(\varepsilon_{R}\) is the relative permittivity of the substrate, \(h\) is the height of the substrate, \(L\) is the length of the patch, \(f_{0}\) is the resonant frequency, and \(c\) is the speed of light. The rectangular patch measures 20.45 mm in width and 17.98 mm in length. To feed an excitation signal to an antenna, the impedance of the antenna and feedline must be matched to normal impedance, i.e., 50 \(\Omega\). A matching line and a microstrip feed line with an input impedance of 50 \(\Omega\) were used to power the proposed antenna. The metal traces on the patch were designed with copper annealed material and totally covered with ground on the antenna's back plane, as illustrated in Figure 6. The dimensions of the rectangular patch antenna are shown in Table 2. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Length (mm)** & **Parameter** & **Length (mm)** \\ \hline L & 53.98 & W & 40.90 \\ L1 & 17.98 & W1 & 21.55 \\ L2 & 10.63 & W2 & 1.64 \\ L3 & 18.61 & W3 & 2.42 \\ GL & 53.98 & GW & 40.90 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Dimensions (length and width) of the proposed rectangular patch antenna. The above designed rectangular patch antenna radiates linearly polarized wave.