## 5 Conclusions  
A novel tri-band circular patch antenna is designed in this study by combining the technology of an off-center probe and a parasitic patch. Three resonant modes of TM\({}_{01}\), TM\({}_{02}\), and TM\({}_{03}\) are achieved and attributed to the coupling effect between the stacked patches; the resonance bandwidth of the proposed antenna is broadened. Specifically, the antenna provides bandwidths of 20 MHz, 260 MHz, and 510 MHz, and antenna gains of up to 6.35 dBi, 6.15 dBi, and 9.42 dBi at \(f_{1}\), \(f_{2}\), and \(f_{3}\), respectively. Moreover, the  
\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
**Ref.** & **IMBW (\%)** & **PG (dB)** & **Effi (\%)** & **XPR (dB)** & **Size (\(\mathbf{\lambda_{0}}^{3}\))** & **Num. of Band** & **Ways to Achieve Multi-Band and Wideband** \\ \hline [1] & 18 & 6 & - & \(\geq\)15 & \(1.35\times 1.35\times 0.02\) & 1 & Shorted vias \\ [2] & 12.2 \& 9.8 & 6 \& 7.5 & \(\geq\)80 & \(\geq\)18 & \(1.35\times 1.35\times 0.03\) & 2 & Stacked patch \& short vias \\ [3] & 9.4 \& 21.6 & 9.8 \& 8.1 & - & \(\geq\)9 & \(1.43\times 1.43\times 0.07\) & 2 & Shorted vias \\ [4] & 14.8 \& 38.4 \& 5.3 & 4.9 \& 5.9 \& 4.95 & - & - & \(0.73\times 0.73\times 0.21\) & 3 & Defected ground structure \\ [5] & 40 \& 62 & 4.6 \& 5.2 & - & \(\geq\)15 & \(0.49\times 0.49\times 0.35\) & 2 & Dual antenna \\ [10] & 4.2 \& 3.9 \& 3.4 & 7.15 \& 6.02 \& 4.38 & - & \(\geq\)30 & - & 3 & Slotting \& stubs \\ [11] & 5 \& 2.1 \& 9.5 & 7.5 \& 8.7 \& 8.7 \& - & \(\geq\)20 & \(0.76\times 0.76\times 0.03\) & 3 & Slotting \& stubs \\ [12] & 1.2 \& 2 \& 1.9 \& 0.9 & 4.6 \& 5.05 & - & \(\geq\)30 & \(0.77\times 0.77\times 0.04\) & 4 & Coupled resonators \\ [18] & 0.8 \& 0.7 \& 0.8 \& 0.7 & 2.4 \& 1.4 \& 2 \& 2.4 & \(\geq\)15 & 0.4 \& 0.4 \& 0.02 & 4 & Shorting \& slotting \\
\begin{tabular}{} \end{tabular} **This work** & **1.1 \& 6.7 \& 9.8** & **6.35 \& 6.15 \& 9.42** & \(\geq\)**85.6** & \(\geq\)**20** & **0.57 \& **0.57 \& \(\times\) 0.02** & **3** & **Off-centerfeeding \& stacked patch** \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison Between Reported and the Proposed Antenna.  
measured results show that differentiated radiation patterns exhibiting broadside radiation, omnidirectional radiation, and three-beam radiation in the three bands are also obtained. Compared with the multiple-band antennas proposed in [10; 11; 18], the antenna designed in this paper has a radiation efficiency of no less than 85% and a simple structure, which suggests that it can be applied to the multi-service field of wireless communication, such as indoor routing, with a stronger penetration ability.  
Theoretical analysis and modeling simulation, M.G. and X.Z.; data collection and processing, M.G. and X.Z.; funding acquisition, M.G. and X.Z.; writing--original draft, M.G. and X.Z.; writing--review and checking, X.Z. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Fundamental Research Funds for the Central Universities under Grant No. 2020 ZDPY0223; the Natural Science Research Funds Project of Hefei Technology College under Grant No. 2021 KJ01; Hefei Technology College High-level Talent Introduction Funding Project No. 2021 KYQDZ007; and the Science and Technology Innovation Team Funding Project of Hefei Technology College No. 2022 Akjcx06.  
Not applicable.  
The data presented in this study are available within the article.  
The authors declare no conflict of interest.