## 3 Antenna Structure Design  
The primary goal of this effort is to achieve a multiband response using the metamaterial principle. Microstrip antennas radiate because of the presence of fringing fields. The presence of fringing fields may explain the radiating action of the microstrip antenna. Patch have the highest current in their midst and the lowest current at their ends. As the patch antenna may be considered an open-circuited transmission line, its voltage reflection coefficient will equal one. If this occurs, the voltage and current are out of phase. Hence, the voltage peaks as the patch nears its end. Around the patch antenna's origin, the voltage has to be at its half-wavelength distance. Therefore, the fields underneath the patch will look like the fringe fields on the patch's edges. Microstrip antenna radiation is the sum of the phase-added E-fields surrounding the antenna. Fringing fields are responsible for the microstrip antenna's emission. The metamaterial approach is used to attain multiband phenomena because they have the advantages of offering wideband, miniaturization and simplicity of integration with different portable devices. Thus, it serves as a viable alternative for constructing multiband antennas. The metamaterial ring loading over the superstrate region will also help to achieve excellent gain as well as provide strengthening of the structure. The proposed three-dimensional design is shown in Figure 1a. The design comprises a simple patch antenna, and the four SRRs are loaded in the superstrate region. The four SRRs enable metamaterial properties in the design. The view of the represented design is observed in Figure 1b. The lateral view of the proposed design is shown in Figure 1c. The size of the square-shaped radiating patch element is \(39.2\) mm. The overall size of the substrate is \(48.2\) mm. The overall outer dimensions of the fourth SRR are \(35.3\) mm. FR4 material is a dielectric material with \(4.4\) dielectric constants [26]. The lower cost of FR4 helps with mass production and FR4 provides ease of fabrication. The thickness of the substrate and superstrate region is \(1.6\) mm. The thickness of the ground, patch and four SRRs is \(1.6\) mm. The patch region is excited by applying input through the coaxial feed. The metamaterial ring is loaded in the superstrate region. There are four SRRs loaded in the superstrate area. The overall dimensions of the four SRRs are lower than the patch area. The resonance frequency of the presented design was calculated using Equations (1) and (2). The metamaterial unit cell is positioned above the inset feed's square patch. As a result, the square-shaped metamaterial ring is smaller in size than the square-shaped patch. \[f_{r}=\frac{X_{mn}}{2\pi a_{e}\sqrt{e_{r}}}c \tag{1}\]  
\[a_{e}=a\bigg{\{}1-\frac{2\text{h}}{\pi\text{a}e_{r}}\Big{(}\ln\frac{\pi\text{ a}}{2\text{h}}+1.7726\Big{)}\bigg{\}}^{1/2} \tag{2}\]where \(f_{r}\) represents the resonating frequency, \(\epsilon_{r}\) is the relative permittivity, \(a_{e}\) is the effective dimension of the ring, The speed of light is represented by \(c\), and the substrate height is \(h\). Finally, the conventional resonance of the cavity is expressed using Equation (3). \[H+t\sqrt{\epsilon_{r}}=(\varnothing_{MS}+\varnothing_{G})\frac{\lambda}{4\pi} \pm N\frac{\lambda}{2} \tag{3}\]  
The ground plane reflected phase is \(\mathcal{O}_{G}\), and \(\mathcal{O}_{MS}\) is the reflecting phase of the metamaterial element. \(N\) is an integer, and the thickness of the metamaterial substrate is \(t\). Changing the value of \(H\) creates a resonance cavity where multiple reflections occur between the patch antenna's ground plane and the metamaterial cell superstrate. An enhancement in antenna gain is possible if the antenna satisfies the standard resonance cavity condition because the reflected waves will go through the unit cell at the same phase as the original wave [27]. The presented structure is fabricated and verified to identify the performance index of the proposed work.