# Low-Profile Dual-Band Reflector Antenna for High-Frequency Applications
## 4 Conclusions  
In this paper, a dual-band MMW/THz high-gain low-profile reflector is proposed. The composite feed, with an \(f_{h}/f_{l}\) ratio of around 5, consists of a lower-band coaxial horn and a higher-band ring-focus feed. The lower-band SRA is a small planar reflectarray, while the higher-band SR is an elliptical SR. Due to the SRs, the dual-band reflector antenna can achieve a low F/D (F/D = 0.2) in both bands. To validate the proposed design method, a scaled dual-band reflector antenna is manufactured, assembled, and its lower-band radiation performance is measured. In the lower band, the proposed antenna achieves a 31.4 dBi peak gain, and the aperture efficiency is about 60.2%. Meanwhile, the proposed antenna achieves a 45.0 dBi peak gain in the higher band, and the aperture efficiency is above 44%. When operating in the lower band, the proposed antenna achieves a relative 2 dB gain bandwidth of about 10%, around \(f_{l}\), while the proposed antenna, when operating in the higher band, achieves a relative 2 dB gain bandwidth of approximately 20%, around \(f_{h}\). The measured results, including the radiation patterns, gain, and reflection coefficient results, all agree well with the simulations. Hence, the effectiveness of the proposed method in designing a high-gain low-profile reflector antenna with dual-band radiation capability is demonstrated. The antenna has the characteristics of low cost and high gain, providing a solution for commercial applications in dual-band communication.  
**Author Contributions:** Conceptualization, S.L. and S.-W.Q.; methodology, S.L. and S.-W.Q.; software, S.L.; validation, S.L. and S.-W.Q.; formal analysis, S.L. and S.-W.Q.; investigation, S.L.; resources, S.-W.Q.; data curation, S.L.; writing--original draft preparation, S.L. and S.-W.Q.; writing--review and editing, S.L. and S.-W.Q.; visualization, S.-W.Q.; supervision, S.-W.Q. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by the Natural Science Foundation of China Projects under Grant U20A20165 and Grant 61721001.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Ref** & **F/D** & **Frequency Range** & \begin{tabular}{c} **Peak Gain** \\ **(Kower/Higher** \\ **Band**)** \\ \end{tabular} & \
\begin{tabular}{c} **Efficiency** \\ **(Higher/Lower** \\ **Band**)** \\ \end{tabular} &
\begin{tabular}{c} **Type * \\ **Band** \\ \end{tabular} \\ \hline
[28] & 0.45 & 21–25.5/31.5–35.5 & 34.6 dBi/38.1 dBi & 52.6\%/54.6\% & Horn + SRA \\
[29] & 0.32 & 3.4–3.8/24.9–36 & 13.0 dBi/32.1 dBi & 42\%/47\% & Dual-band horn + SR \\
[30] & 0.3 & 35/94 & 43.6 dBi/51.3 dBi & 26.6\%/21.8\% & Dual-band horn \\
[31] & 0.5 & 65–80/115–125 & 20.3 dBi/21.9 dBi & 4.8\%/2.7\% & Dual-band horn \\
[32] & 1 & 35.5/94 & 44.1 dBi/49.6 dBi & 40.6\%/20.5\% & Dual-band horn \\
[33] & 1.95 & 20–28/65–75 & 23.2 dBi/30.7 dBi & 43.8\%/33.7\% & Dual-band horn \\ This work & 0.2 & 29.4–32.4/142–174 ** & 31.4 dBi/45.0 dBi & 59.0\%/44.0\% & Composite horn + SRA \\ \hline \hline \end{tabular}  
* Type represents the form of feed and SR. ** The frequency range is the simulated frequency range.  
\end{table}
Table 3: Comparison between references and our work.