# A Compact Triple Band Antenna Based on Multiple Split-Ring Resonators for Wireless Applications
## 3 Results and Discussion
As the frequency rises to 3.5 GHz, the current begins to concentrate more on the second, smaller split-ring resonator (SRR 2). This redistribution of current means that the second ring takes the responsibility for resonance, since its shorter electrical length matches better with the shorter wavelength at 3.5 GHz. At 4.8 GHz and 6.8 GHz, the current is concentrated in the third and fourth rings, which consist of the smallest elements in the design. Their small size and close coupling enable effective resonance and wide frequency bands. Figure 9 shows the effectiveness of design development in improving gain. The gain characteristics of the antenna stages show a clear and progressive improvement as the number of integrated SRRs increases. Starting with antenna 1, which contains a single SRR, the gain is relatively low, peaking at about 1.1 dB and covering a single frequency band. With each additional SRR from antenna 2 to antenna 4, not only does the peak value increase, but the gain also becomes more stable over a wider frequency band. It is noteworthy that antenna 4 with four SRRs achieves the highest gain of about 3.2 dB, indicating that the successive integration of SRRs significantly improves the antenna gain. Figure 8: Simulated surface current distributions the proposed multi-SRR-Based antenna at (a) 2.65 GHz, (b) 3.5 GHz, (c) 4.8 GHz and (d) 6.8 GHz. Table 3 summarizes the frequency characteristics of the different SRR-loaded antenna designs (from reference patch antenna to antenna 4). As shown in Figure 3 and interpreted in Figure 5a, the smaller ring (SRR 4) resonates at higher frequencies, while the larger ring (SRR 1) resonates at lower frequencies, as the resonant frequency of each ring is determined by its effective electrical length. In addition, the mutual coupling between the rings increases the antenna's ability to cover a wide frequency band, especially in the higher bands. As observed in Table 3, the radiation efficiency of the proposed antenna is improved despite the use of FR4. This improvement can be attributed to two primary design strategies. First, the use of multi-resonant elements enhances surface current distribution (as illustrated in Figure 8) and effectively suppresses surface wave propagation, thereby reducing radiation losses. Second, the integration of split-ring resonators, known for their strong electromagnetic coupling and field localization capabilities, contributes to miniaturization while enhancing efficiency. SRRs help mitigate substrate-induced losses by concentrating the electromagnetic fields and reducing dielectric absorption. In contrast, the reference antenna exhibits low efficiency (35.7%), which is primarily due to higher substrate losses from the FR4 material and the lack of structural optimization. \begin{table}
\begin{tabular}{p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt}} \hline \hline \multirow{2}{*}{**Antennas**} & **No. of Band** & **Frequency Band (GHz)** & **Bandwidth in \%** & **Peak Gain (dBi)** & **Directivity (dBi)** & **Efficiency \%** \\ \hline
**Reference patch antenna** & Band 1 & 2.47–2.53 & 2.5 & 2.41 & 1.88 & 6.35 & 35.7 \\ \hline
**Antenna 1** & Band 1 & 2.35–3 & 2.69 & 24.34 & 1.1 & 3.12 & 62.8 \\ \hline
**Antenna 2** & Band 1 & 2.4–2.8 & 2.68 & 15.38 & 1.1 & 3.14 & 62.5 \\  & Band 2 & 3.25–4.25 & 3.55 & 26.66 & 1.1 & 3.08 & 63.5 \\ \hline
**Antenna 3** & Band 1 & 2.4–2.77 & 3.66 & 14.34 & 1.1 & 3.12 & 62.8 \\  & Band 2 & 3.25–3.77 & 3.49 & 15.56 & 1.2 & 3.26 & 62.2 \\  & Band 3 & 4.5–6.47 & 4.9/5.8 & 35.94 & 2.02 & 3.56 & 70.3 \\ \hline
**Antenna 4** & Band 1 & 2.4–2.80 & 2.65 & 14.55 & 1.5 & 3.11 & 69.1 \\
**(Proposed antenna)** & Band 2 & 3.25–3.75 & 3.47 & 14.28 & 2 & 3.2 & 75.9 \\
**antenna 3** & Band 2 & 4.5–7.84 & 4.8/6.6 & 54.13 & 3.1 & 4.52 & 72.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Frequency characteristics comparison of various SRR-loaded antenna designs. Figure 9: Gain performance of antenna design steps with incremental SRR integration.