## 2 Design of the Metamaterial Unit Cell  
In the unit cell construction, a mutually linked double C-shaped metal with an interconnected double SRR was proposed. The design structure is shown in Figure 1a, which presents the geometric structure of the metamaterial unit cell with a front view of the structure. The design of the proposed metamaterial unit cell was implemented with a Rogers RT5990 substrate with a dimension of \(8\times 8\) mm\({}^{2}\) and a substrate thickness of 1.575 mm. The dielectric constant and loss tangent of the substrate is \(\varepsilon_{\mathrm{r}}\) = 2.2 and \(\delta\) = 0.0009, respectively. The used copper coating has a thickness of 0.035 mm and a width of 0.4 mm, with an electrical conductivity of \(\sigma=5.8\times 10^{7}\) S/m. The double SRR attached double C-shaped metamaterial schematic and 3D diagram are shown in Figure 1b-d. Figure 1b exhibits the layers of the metamaterial unit cell where there is a substrate layer and a copper coating layer; Figure 1c shows the perspective view of the unit cell; Figure 1d indicates the side view of the design. The unit cell consists of two square SRR bounded with two C-shaped interconnected parts. The design is achieved with modification of the position, length, and width of the shapes by several numerical simulations executed in the CST Microwave Studio Suite (2019). Figure 2 represents the design progress from beginning to end; Figure 3 represents the transmission coefficients and reflection coefficients from the different design structures. The design was attempted with an outer SRR, which is shown in Figure 2a-Design 1. The gap between the edge of the substrate and the outer SRR is 0.2 mm. The length, width, and height of the very first SRR are 7.6 mm, 7.6 mm, and 0.035 mm, respectively. There is a split gap of 0.2 mm at the top-right side of the SRR. When the incident wave is propagated on the device, the resonance is observed there by the SRR as the conducting part of the SRR shows inducting properties and the split gap creates the capacitance. As shown in Figure 3a, there are three resonances of transmission coefficient found because of the outer SRR at 3.53 GHz, 10.29 GHz, and 13.42 GHz. Figure 1: (**a**) Unit cell design parameters and (**b–d**) schematic and 3D structure of the proposed metamaterial unit cell. Figure 2: Design evolution of metamaterial unit cell. It is observed that the four resonance frequencies are in three different bands, the S, X, and Ku bands, respectively. The reflection coefficient is shown in Figure 3b, where two strong resonances are observed at 5.2 GHz and 12.6 GHz. In Figure 2b-Design 2, when the second outer SRR is introduced at the inner part of the existing SRR, we observed there is a left shifting of the resonance frequencies. The updated transmission coefficients are 3.4 GHz, 9.2 GHz, and 12.9 GHz--see Figure 3a; the updated reflection coefficients are 4.6 GHz and 11.3 GHz--see Figure 3b. In Figure 2c-Design 3, the C-shape SRR is introduced at the inner part of the existing two SRRs; we find that a new resonance frequency is added with a strong bandwidth at 8.7 GHz. The new transmission coefficient is shown in Figure 3a along with the other resonance frequencies, 3.4 GHz, 8.7 GHz, 9.2 GHz, and 12.8 GHz, respectively. The new reflection coefficient at 10.8 GHz is also compared in Figure 3b with the other frequencies, 4.5 GHz, 10.8 GHz, and 11.2 GHz, respectively. In Figure 2d-design 4, we introduce a new C-shape SRR in the very inner part of the whole structure and we find almost the same resonance frequencies over the transmission coefficient (S21) in Figure 3a and reflection coefficients (S11) in Figure 3b. The transmission coefficients and reflection coefficients are 3.4 GHz, 8.7 GHz, 9.2 GHz, and 12.8 GHz and 4.5 GHz, 10.8 GHz, and 11.2 GHz, respectively. Finally, in Figure 2e-Proposed design, we interconnect the C-shape SRRs to make a double C-shape and interconnect the outer two SRRs.