# A Compact Triple Band Antenna Based on Multiple Split-Ring Resonators for Wireless Applications
## 3 Results and Discussion  
The S11 parameter results for antenna 1 to antenna 4 (proposed antenna) are shown in Figure 5a, while the step-by-step scalable equivalent circuit model is illustrated in Figure 5c. As can be seen in Figure 5a, antenna 1 with a single octagonal ring achievesa single resonant frequency band from 2.35 GHz to 3 GHz, with a maximum return loss of \(-30\) dB at 2.69 GHz and a bandwidth of 24.34%. When SRR 2 is added in antenna 2, a second resonant frequency occurs and forms bands at 2.4-2.8 GHz and 3.25-4.25 GHz, with maximum return losses of \(-29\) dB and \(-34\) dB at 2.68 GHz and 3.55 GHz, respectively. The introduction of this second band demonstrates good multiband operation without compromising the original 2.5 GHz band. Following the simulation results, antenna 3 with three rings has three separate resonant frequency bands: 2.4-2.77 GHz, 3.25-3.77 GHz and a wide band from 4.5 GHz to 6.47 GHz. This wider third band, which has peak return losses of \(-43\) dB at 4.9 GHz and \(-37\) dB at 5.8 GHz, has better broadband characteristics. The additional bandwidth of the third band (35.94%) emphasizes the better ability to cover the higher frequencies. The final design, antenna 4, adds a fourth ring and achieves three optimized bands of 2.4-2.8 GHz, 3.25-3.75 GHz and a significantly extended broadband range of 4.5 GHz to 7.84 GHz. The peak return losses of \(-31\) dB, \(-37\) dB and \(-35/-25\) dB within these bands indicate good impedance matching, with the widest bandwidth of 54.13% being achieved in the highest band. Figure 5: Proposed multi-SRR-based antenna. (**a**) Comparative S11 simulation results of various SRR-loaded antenna designs. (**b**) Comparison between the equivalent circuit model (ADS) and the layout simulation (CST). (**c**) Scalable equivalent circuit model. Figure 5b compares the simulated return losses (S11) of the proposed antenna design, which were determined using ADS and CST. Both results show multiple resonant frequencies, indicating multiband operation. The strong agreement in the resonant positions and bandwidths confirms the effectiveness of the equivalent circuit model in predicting the antenna behavior. Figure 6a shows the design and electromagnetic response of the proposed metamaterial structure based on multiple split-ring resonators. The real part of the permeability, as shown in Figure 6b, shows that the MTM exhibits negative permeability at certain resonant frequencies. These frequencies coincide with the resonant frequencies observed in the S11 parameter plot of the proposed multi-SRR-based antenna (Figure 5a). This strong correlation confirms that the negative permeability introduced by the MTM plays an important role in achieving multiband resonance and miniaturization of the antenna. Figure 7a shows the real and imaginary curves of the input impedance of the antenna over the entire frequency range. In the 2.4-2.8 GHz, 3.25-3.75 GHz and 4.5-7.84 GHz bands, the real part of the impedance is about 50 \(\Omega\), while the imaginary part is close to 0 \(\Omega\), indicating excellent impedance matching. Figure 7b shows the corresponding VSWR curve falling below 2 in these frequency bands, further confirming the good impedance matching at the resonant frequencies. These results are consistent with the reflection coefficient observed in Figure 5a and confirm that the antenna operates efficiently in the targeted frequency bands. Figure 6: Proposed metamaterial structure based on multiple SRRs. (**a**) Design. (**b**) Real part of permeability. Figure 7: The proposed antenna: (**a**) real and imaginary of the input impedance and (**b**) VSWR. Table 2 shows the resonant frequencies of the proposed multi-SRR-based antenna, which were determined by equivalent circuit analysis, numerical simulations and analytical calculations.