## 2 Materials and Methods
### Design of Wideband Antenna  
The proposed reconfigurable antenna was originally inspired by a conventional quarter-wave rectangular monopole antenna, and the basic concept of the proposed antenna and designed methodology was already presented in [19]. The length (\(L_{R}\)) of the rectangular monopole antenna could be estimated by using the following equation provided in [20]:  
\[L_{R}=\frac{C_{o}}{4f_{c}\sqrt{\epsilon_{eff}}} \tag{1}\]  
where \(C_{o}\) represents the speed of light in free space, \(f_{c}\) represents the central frequency; for the presented case it was selected to be 4 GHz, whereas, \(\epsilon_{eff}\) is the effective dielectric constant of the substrate is calculated by using the following relation:  
\[\epsilon_{eff}\approx\frac{\epsilon_{r}+1}{2}+\frac{\epsilon_{r}-1}{2}\left\{ \left(1+12\frac{A_{Y}}{H}\right)^{-0.5}\right\} \tag{2}\]  
where \(H\) is the thickness of the substrate, and \(A_{Y}\) is the width of the substrate.  
The resultant antenna resonates at 3.8 GHz with an impedance bandwidth of 850-MHz ranging 3.55-4.4 GHz, as depicted in Figure 2. Although the antenna offers a wide impedance bandwidth, still it does not cover the targeted 5G sub-6-GHz band (3.1-4.5 GHz) allocated globally for future wireless communications. Thus, perturbation techniques were utilized to widen the impedance bandwidth of the antenna. Different from common  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Value** & **Parameter** & **Value** & **Parameter** & **Value** \\ \hline A\({}_{X}\) & 30 mm & A\({}_{Y}\) & 30 mm & H & 1.9 mm \\ G\({}_{X}\) & 12 mm & F\({}_{X}\) & 30 mm & F\({}_{Y}\) & 1.9 mm \\ P\({}_{X}\) & 15.55 mm & P\({}_{Y}\) & 30 mm & g & 1 mm \\ d & 1 mm & L\({}_{1}\) & 12.72 mm & L\({}_{2}\) & 9.9 mm \\ C\({}_{1}\) & 100 pF & I & 68 nH & C\({}_{DC}\) & 100 pF \\ \hline \hline \end{tabular}
\end{table}
Table 1: Dimension of the various parameter length of the proposed antenna.  
Figure 1: Geometrical configuration of proposed antenna: (**a**) top-view (**b**) bottom-view (**c**) side-view.  
techniques including DGS and slots to achieve wideband behavior, this design employed truncation of radiator corners to improve the bandwidth. Both lower corners were truncated using an equilateral triangle which results in increasing the effective length of the radiator, thus shifting of resonance toward the lower frequencies, as depicted in Figure 2. Moreover, truncation of the corner causes more current to flow from the feedline to the radiator. Due to the triangular shape, the current uniformly distribute itself on the surface of the radiator. The increase in flow and uniform distribution of current resulted in improvement in impedance matching at lower frequencies to enhances the impedance bandwidth of the antenna. The resultant antenna exhibits a wide impedance bandwidth of 2.2 GHz ranging 2.35-4.55 GHz which corresponds to 62.8% of central frequency, as depicted in Figure 2. It is worthy to note here that besides 5G sub-6-GHz band spectrum the antenna also covers 2.4 GHz WLAN band, 2.45 GHz ISM band, 2.5 GHz Wi-Max band, and more than 90% of S-band (2-4 GHz), thus making it suitable for multiple applications.