# Low-Profile Antenna System for Cognitive Radio in IoST CubeSat Applications
## 4 Conclusions  
This work presents a low-profile WB and NB frequency reconfigurable antenna for IoST applications. The proposed antenna consists of a circularly polarized WB semi-hexagonal slot and two NB frequency reconfigurable loop slots integrated on the same substrate board. The semi-hexagonal-shaped slot antenna is excited by two orthogonal \(\pm 45^{\text{o}}\) tapered feed lines and loaded by a capacitor in order to achieve left/right-handed circular polarization in a wide bandwidth from 0.57 GHz to 0.95 GHz. The frequency reconfigurable antenna operates over a wide band from 0.6 GHz to 1.05 GH using a single varactor diode per antenna element. The two NB antennas are designed as meander loops to miniaturize the physical length and reactive loading, which further optimized it to be operated in sub-GHz bands. The antenna system is fabricated on FR-4 substrate with a dimension of 100 \(\times\) 100 \(\times\) 0.76 mm\({}^{3}\). The measured results verified the simulated results  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Ref.** & **Size \((\text{mm}^{3})\)** & \(f\)**(GHz)** & **Reconfigurability** & **Low Profile** & \
\begin{tabular}{c} **Support** \\ **UHF** \\ \end{tabular} &
\begin{tabular}{c} **Pattern** \\ **Diversity** \\ \end{tabular} & **Polarization** & **Remarks** \\ \hline
[3] & \(87\times 87\times 27.5\) & 1.575 & No & No & No & CP & Helix \\ \hline
[8] & \(60\times 60\times 1.52\) & 0.4 & No & Yes & Yes & No & Dual CP & Slot antenna \\ \hline
[35] & \(100\times 100\times 100\) & 0.45 & No & No & Yes & Yes & LP &
\begin{tabular}{c} Folded slot \\ antenna \\ \end{tabular} \\ \hline
[38] & \(100\times 100\times 25\) & 0.9/5.8 & No & No & No & No & CP &
\begin{tabular}{c} Microstrip \\ antenna with \\ shaped ground + \\ [PERSON] \\ \end{tabular} \\ \hline
[40] & \(100\times 100\times 7.2\) & 2.5 & No & Yes & No & No & CP &
\begin{tabular}{c} 2 Substrate + 2 foam layers \\ \end{tabular} \\ \hline
[44] & \(100\times 100\times 100\) & 6 & Yes & No & No & Yes & LP & 3D structure \\ \hline
[47] & \(110\times 110\times 3.18\) & 1.575/2.2 & No & Yes & No & No & CP &
\begin{tabular}{c} Stacked patch \\ antenna of \\ three layers \\ \end{tabular} \\ \hline
[46] & \(100\times 100\times 1.6\) & 3.2/9.3 & No & Yes & No & Dual LP &
\begin{tabular}{c} Shared aperture \\ antenna \\ \end{tabular} \\ \hline
[48] & \(100\times 100\times 5.5\) & 1.69/2.45 & No & Yes & No & CP &
\begin{tabular}{c} Conical shape \\ spiral antenna \\ \end{tabular} \\ \hline
[49] & NA (1.5 U) & 0.48 & No & Yes & Yes & No & LP &
\begin{tabular}{c} Slot antenna on \\ solar panel \\ \end{tabular} \\ \hline
[50] & \(159\times 152\times 3.25\) & 2.4 & Manual & Yes & No & No & LP & \
\begin{tabular}{c} Patch/monopole \\ antenna \\ \end{tabular} \\ \hline Proposed & \(100\times 100\times 1.52\) & 0.55 & Yes & Yes & Yes &
\begin{tabular}{c} Design antenna \\ + two \\ communication \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison between reported antennas and the proposed antenna.  
and both are in good agreement. The proposed antenna design is well suited for IoT CubeSat applications.  
Conceptualization, K.A. and R.H.; data curation, K.S. and Q.H.A.; formal analysis, K.A. and M.I.; project administration, R.H.; resources, K.A. and Q.H.A.; software, R.H. and K.S.; validation, K.S. and A.H.H.A.; visualization, R.H. and M.I.; writing--original draft, K.S. and A.H.A.; writing--review and editing, K.A. and Q.H.A. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors would like to acknowledge the support provided by Researchers Supporting Project number (RSP2023R474), King Saud University, Riyadh, Saudi Arabia.  
The authors declare no conflict of interest.