# A Multi-Frequency Omnidirectional Antenna Based on a Ring-Shaped Structure
## 5 Conclusions  
In this paper, we design and simulate a new multi-frequency omnidirectional microstrip antenna using CST simulation software. The split-ring resonator structure on the antenna surface and the defect ground state structure on the back of the antenna can effectively control the surface current distribution and increase the resonant frequency of the antenna, effectively increasing the number of operating frequency bands. The measurements are in general agreement with the simulations. The proposed antenna can work nicely in 5G NR (FR1, 0.45-3 GHz), 4 GLTE (1.6265-1.6605 GHz), Personal Communication System (1.85-1.99 GHz), Universal Mobile Telecommunications System (1.92-2.176 GHz), WiMAX (2.5-2.69 GHz), and other communication frequency bands. The antenna also has excellent omnidirectional radiation properties in different operating frequency bands, which meet the requirements of portable multi-band mobile devices and are of practical engineering interest and utility.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Ref**} & **Antenna Size** & **Resonance** & **The Number of** & & \\  & **Comparison** & **Frequency\(f_{0}\)** & **\(-\)10 dB** & **\(-\)10 dB Bandwidth (GHz)** & **Maximum Gain** \\  & **(L \(\times\) W mm\({}^{2}\))** & **(GHz)** & **Bandwidth** & & **–**10 dB Bandwidth (GHz)** & **Maximum Gain** \\ \hline
[6] & 20 \(\times\) 20 & 1.35/2.57/4.57/5.21 & 4 & 1.3–1.39/2.52–2.63/ & - \\
[15] & 26 \(\times\) 22 & 1.836/3.72/4.32 & 3 & 1.495–2.180/3.35–4.08/4.15–4.49 & 2.43 dBi \\
[20] & 43.6 \(\times\) 43.6 & 0.829/2.20/1.575/2.450 & 4 & 0.698–0.960/1.710–2.690/1.575/ & 5.3 dBi \\
[22] & 28.05 \(\times\) 24.90 & 1.226/1.582 & 2 & 1.217–1.235/1.567–1.597 & - \\
[24] & 50 \(\times\) 50 & 2.4/3.5/4.8 & 3 & 1.88–2.73/3.26–3.79/4.7–5.9 & 4.7 dBi \\
[25] & 100 \(\times\) 60 & 2.45/3.50/5.31 & 3 & 2.17–2.72/3.34–3.66/4.85–5.77 & 3.89 dBi \\
[27] & 17 \(\times\) 17 & 1.65/5.90 & 2 & 1.12–2.4/8.7–0 & 3 dBi \\  & & & 1.097–1.109/1.319–1.329/ & & \\ Proposed & 62 \(\times\) 42 & 1.10/1.33/1.63/ & 6 & 1.628–1.635/1.964–1.971/ & 4.63 dBi \\  & & & 2.071–2.078/2.69 & 2.071–2.078/2.679–2.691 & & \\ \hline \end{tabular}
\end{table}
Table 2: Research results of multi-frequency antennas.  
Figure 8: Simulated and measured reflection coefficient of the proposed antenna.  
**Author Contributions:** Conceptualization, H.G., [PERSON] ([PERSON]) and J.W.; methodology, H.G., Q.W. and Y.H.; software, [PERSON] ([PERSON]) and J.W.; validation H.G. and Y.C. ([PERSON]); formal analysis, H.G. and Q.W.; investigation, J.W.; resources, Y.H.; data curation, H.G.; writing--original draft preparation, H.G.; writing--review and editing, Q.W., [PERSON] ([PERSON]) and J.W.; visualization, [PERSON] ([PERSON]); supervision, [PERSON] ([PERSON]) and M.L.; project administration, M.L.; funding acquisition, Q.W. and M.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Double First-Class Disciplines National First-Class Curriculum Construction, the National Future Technical College Construction Project, the Shanxi Province Postgraduate Education Reform Project, grant numbers 11013168 and 11013410, 11013169, 11012103 and 11012133.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data that support the findings of this study are available from the corresponding author upon reasonable request.  
**Conflicts of Interest:** The authors declare no conflict of interest.