**5. Discussion**

The quantitive comparison of similar antennas has been given in Table 2. For the 2G/3G/4G/5G base station applications, the wide bandwidth is necessary to cover the 2G, 3G, and 4G bands and the new sub-6 GHz 5G frequency bands. Hence, only sub-6 GHz frequency band of the proposed antenna is shown here. Besides, the gain, HPBW, and the electrical size should be considered simultaneously for the base station antenna. From Table 2, we can see that the lowest operating frequency of the proposed plasmonic AVA is the lowest (1.8 GHz). The electrical size is 0.56λ0, which is a little larger than that of Refs. [31–33], where λ<sup>0</sup> is the wavelength in the air corresponding to the lowest operating frequency. The minimum gain (5.5 dBi) is the highest, since high gain is necessary for the base station antenna.


**Table 2.** Comparison of the similar antennas.

## **6. Conclusions**

Here, a broadband and miniaturized plasmonic antipodal Vivaldi antenna is designed and measured, where plasmonic metamaterials are loaded on the antipodal Vivaldi antenna to improve the antenna performance. Compared of the typical AVA, the electrical size of the plasmonic AVA is reduced. The operating frequency is from 1.8 GHz to 6 GHz, which covers the 2G/3G/4G/5G communication band. The simulated and measured results of the plasmonic agree well. The measured results show that the radiation pattern of the plasmonic AVA is stable and the average gain of the antenna is 7.24 dBi.

**Author Contributions:** Conceptualization, Y.J.Z.; data curation, L.H.D.; formal analysis, L.H.D.; methodology, L.H.D.; resources, C.T.; writing—original draft preparation, L.H.D.; writing—review and editing, Y.J.Z.; supervision, Y.J.Z.; project administration, Y.J.Z.; funding acquisition, C.T. and Y.J.Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Natural Science Foundation of China, grant number 61971469, and by Science and Technology Commission Shanghai Municipality (STCSM), grant numbers 18ZR1413500 and SKLSFO2017-05.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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