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\begin{document}

\title{Metasurface-Backed UWB Antenna Providing Enhanced Radiation and Bandwidth Stability}

\author{
\IEEEauthorblockN{Ahmed S.~I.~Amar}
\IEEEauthorblockA{\textit{Egyptian Technical Research and}\\
\textit{Development Centre}\\
Cairo, Egypt\\
ahmed.s.i.amar.adc@alexu.edu.eg}
\and
\IEEEauthorblockN{Mohamed Boumalkha}
\IEEEauthorblockA{\textit{Department of Physics, Faculty of Sciences}\\
\textit{Moulay Ismail University}\\
Meknes, Morocco\\
med.boumalkha@gmail.com}
\and

\IEEEauthorblockN{Zakaria Che~Muda}
\IEEEauthorblockA{\textit{Faculty of Engineering and}\\
\textit{Quantity Surveying}\\
\textit{INTI-IU University}\\
Nilai, Malaysia\\
zakaria.chemuda@newinti.edu.my}

\and

\IEEEauthorblockN{Ahmed Samir}
\IEEEauthorblockA{\textit{Department of Electronics and}\\
\textit{Communication Engineering}\\
\textit{Uruk University}\\
Baghdad, Iraq\\
Ahmed.S.ahmed@uruk.edu.iq}
\and
\IEEEauthorblockN{Tamer Shamseldin}
\IEEEauthorblockA{\textit{Technical Research Center}\\
Cairo, Egypt\\
tamer@alumni.purdue.edu}

}



\maketitle



\begin{abstract}
This study presents a novel UWB antenna featuring optimized radiation and incorporating a metamaterial-inspired design. The antenna utilizes a CPW-fed circular monopole paired with an 8$\times$8 metasurface composed of low-profile metamaterial cells. Each cell has four star-shaped slots with identical arms, which contribute to the antenna's distinct electromagnetic characteristics. Both the antenna and metasurface are organized on an FR4 substrate. The results indicate that the design effectively covers the 3.1-10.6 GHz UWB frequency spectra, offering strong frequency response, high radiation efficiency, and satisfactory gain. This antenna design is highly suitable for UWB applications, fulfilling the demanding specifications of contemporary wireless communication systems. This research work directly supports SDG 9 (Industry, Innovation and Infrastructure) by advancing the resilient and innovative communication infrastructure crucial for global connectivity.
\end{abstract}

\begin{IEEEkeywords}
star-shaped slot metamaterials, enhanced radiation, UWB communications.
\end{IEEEkeywords}



\section{Introduction}
The rapid evolution of wireless communication technologies has significantly increased the demand for antennas that can deliver high performance across wide frequency ranges. As the world transitions toward next-generation systems like 5G and 6G, ultra-wideband (UWB) antennas are becoming increasingly indispensable for enabling high-speed data transfer, ensuring seamless connectivity, and supporting a broad spectrum of modern applications [1-2]. UWB systems, renowned for their ability to facilitate efficient communication over vast bandwidths, are poised to play a pivotal role in driving the adoption of cutting-edge technologies, including high-definition multimedia streaming, advanced radar systems, medical diagnostics, smart devices, and the Internet of Things (IoT) [3-4]. These technologies rely on robust, efficient antennas to maintain connectivity and deliver high-performance data services.

A significant challenge in UWB antenna design is the need for solutions that are not only compact and efficient but also capable of operating effectively across expansive frequency bands without sacrificing radiation performance, bandwidth, or other key metrics [5-6]. 

As the demand for smaller, more powerful devices grows, finding ways to optimize antenna size and functionality while maintaining superior performance becomes increasingly vital. One innovative approach to addressing these challenges is the incorporation of metamaterials—engineered materials with unique electromagnetic properties that do not exist in naturally occurring materials [7-8]. Metamaterials are designed to interact with electromagnetic waves in unconventional ways, enabling the manipulation of wave propagation and significantly enhancing the performance of antenna systems.

Among the various metamaterial structures, meta-surfaces have emerged as an up-and-coming solution. These two-dimensional, periodic structures can manipulate electromagnetic waves in specific ways, offering the potential to control key parameters like bandwidth, gain, radiation patterns, and efficiency. By integrating metasurfaces into antenna designs, it is possible to enhance the performance of UWB antennas, making them more versatile and capable of meeting the stringent requirements of modern wireless communication systems [9, 10]. 

The integration of metasurfaces into UWB antenna designs not only enhances their ability to operate over broad frequency ranges but also allows for more compact, efficient, and high-performing solutions that can be easily integrated into a wide range of applications. As wireless technologies continue to evolve, the role of metasurfaces in antenna design is expected to grow, offering exciting possibilities for next-generation communication systems.

This study presents an advanced UWB antenna design that utilizes the benefits of a metasurface to enhance radiation characteristics and bandwidth. The proposed antenna features a monopole resonator, complemented by an 8$\times$8 metasurface array. Each unit cell is formed of four star-shaped slots with identical arms, which enhances the antenna's performance. The design has been developed and evaluated using CST Microwave Studio [10], [11], with a focus on optimizing radiation performance and spectral rejection.




\section{Antenna Design Details}

Figure \ref{fig:fig1} illustrates the schematic of the suggested enhanced-gain monopole antenna design. The design features a simplified structure comprising a monopole antenna with a CPW-fed technique. Both the monopole antenna and the 8$\times$8 metasurface are designed on a 1.6 mm FR-4 substrate, characterized by $\epsilon = 4.4$ and $\delta = 0.022$. Table \ref{tab:parameters} lists the design parameter values in mm units.


\begin{figure}[htbp]
     \centering
     \begin{subfigure}[b]{0.4\textwidth}
         \centering
         \includegraphics[width=\textwidth]{IMG_2233.jpeg}
         \caption{Top view of the antenna}
         \label{fig:fig1a}
     \end{subfigure}
     \\ % Forced line break for two rows
     \begin{subfigure}[b]{0.4\textwidth}
         \centering
         \includegraphics[width=\textwidth]{IMG_2234.jpeg}
         \caption{Side view showing the gap distance}
         \label{fig:fig1b}
     \end{subfigure}
     \caption{Metamaterial-based antenna design showing top and side perspectives.}
     \label{fig:fig1}
\end{figure}

\begin{table}[htbp]
\caption{Parameter Values}
\begin{center}
\begin{tabular}{|c|c|c|c|c|c|c|}
\hline
\textbf{Param.} & W & L & W\textsubscript{1} & L\textsubscript{1} & W\textsubscript{2} & L\textsubscript{2} \\ \hline
\textbf{mm} & 131.5 & 10 & 26 & 31.8 & 3.4 & 18 \\ \hline
\textbf{Param.} & W\textsubscript{3} & L\textsubscript{3} & W\textsubscript{4} & L\textsubscript{4} & W\textsubscript{x} & d \\ \hline
\textbf{mm} & 6 & 2 & 0.25 & 6 & 16.5 & 19.5 \\ \hline
\end{tabular}
\label{tab:parameter_values}
\end{center}
\end{table}




\section{The Unit Cell Characteristics}


The feeding diagram and schematic of the MTM cell are illustrated in Figs. \ref{fig:fig2} (a) and (b). As shown, it contains a square copper structure with four star-shaped slots. 


\begin{figure}[htbp]
     \centering
     \begin{subfigure}[b]{0.24\textwidth}
         \centering
         \includegraphics[width=\textwidth]{IMG_2235.jpeg}
         \caption{Feeding mechanism}
         \label{fig:fig2a}
     \end{subfigure}
     \hfill % Space between columns
     \begin{subfigure}[b]{0.24\textwidth}
         \centering
         \includegraphics[width=\textwidth]{IMG_2236.jpeg}
         \caption{Unit cell dimensions}
         \label{fig:fig2b}
     \end{subfigure}
     \caption{Detailed design of the MTM unit cell (a) feed structure and (b) geometry.}
     \label{fig:fig2}
\end{figure}



Figure \ref{fig:fig3} depicts the S-parameters ($S_{11}$/$S_{21}$) of the designed MTM unit cell. As demonstrated, an excellent stopband performance has been achieved, extending from 3 GHz to beyond 10.6 GHz, showing that the metamaterial structure effectively suppresses unwanted frequencies within this range. This result confirms the successful design of the MTM unit cell for enhancing the antenna's performance by blocking interference and maintaining efficient operation across the desired frequency spectrum.


\begin{figure}[htbp]
\centerline{\includegraphics[width=0.45\textwidth]{IMG_2237.jpeg}}
\caption{S-parameters ($S_{11}$ and $S_{21}$) of the designed MTM unit cell.}
\label{fig:fig3}
\end{figure}

\begin{figure}[h!]
    \centering
    \includegraphics[width=0.48\textwidth]{IMG_2238.jpeg}
    \caption{Phase response of the proposed MTM unit cell over the frequency range of 2–12~GHz.}
    \label{fig:fig4}
\end{figure}

Furthermore, Figure \ref{fig:fig4}   demonstrates the stable and continuous phase response of the proposed MTM unit cell over the 2–12 GHz band, confirming its suitability for wideband UWB applications with minimal phase distortion. These results indicate stable and consistent phase behavior, ensuring that the unit cell performs effectively in a wide frequency band while maintaining minimal distortion. The overall behavior of the MTM unit cell shows excellent agreement with the desired performance for UWB applications.






\section{Performance Analysis of the Proposed Antenna Design }


The suggested metasurface is placed underneath the monopole antenna, with a distance of $d = 19.5$ mm. Both components are made from economical FR-4 material, each having a thickness of 1.6 mm. Figure \ref{fig:fig6} presents the return losses of the UWB antenna, both with and without the integration of the metasurface. 

\begin{figure}[htbp]
    \centering
    \includegraphics[width=0.48\textwidth]{IMG_2239.jpeg}
    \caption{}
    \label{fig:fig5}
\end{figure}

\begin{figure}[htbp]
    \centering
    \includegraphics[width=0.48\textwidth]{IMG_2240.jpeg}
    \caption{Return loss ($S_{11}$) comparison of the UWB antenna with and without the metasurface integration.}
    \label{fig:fig6}
\end{figure}

The results clearly indicate that the monopole antenna meets the required bandwidth specifications in both configurations, demonstrating effective performance across the desired frequency range. The antenna exhibits stable operation, whether the metasurface is incorporated or not, suggesting that the overall design maintains its functionality while benefiting from the metasurface integration.




\begin{figure}[htbp]
\centerline{\includegraphics[width=0.45\textwidth]{IMG_2241.jpeg}}
\caption{Gain levels of the monopole antenna with and without the metasurface.}

\label{fig:fig7}
\end{figure}



Additionally, Figure \ref{fig:fig7} compares the maximum gain levels of the antenna with and without the metasurface. As shown, incorporating the metasurface results in a significant increase in the antenna's gain, which is one of the primary goals of utilizing metamaterials in antenna design. 

Specifically, the gain improves from approximately 2–5 dBi without the metasurface to a range of 6–9.5 dBi with the metasurface, showcasing the substantial enhancement in performance. This increase in gain is critical for applications requiring higher directivity and more efficient signal transmission, further solidifying the potential of the proposed metasurface-based antenna for advanced communication systems. The results highlight the importance of metamaterial integration in achieving the dual objectives of broad bandwidth and high gain, making this design particularly suitable for next-generation wireless systems that demand both wide coverage and enhanced signal strength [7].


\begin{figure}[htbp]
    \centering
    \includegraphics[width=0.48\textwidth]{IMG_2242.jpeg}
    \caption{2D radiation patterns of the basic monopole antenna at (a) 5 GHz and (b) 9 GHz.}
    \label{fig:fig8}
\end{figure}



The simulated three-dimensional radiation patterns of the basic monopole antenna at 5 GHz and 9 GHz are presented in Fig. \ref{fig:fig8}. As illustrated, the antenna exhibits stable and nearly omnidirectional radiation characteristics across both frequencies. This consistent radiation behavior indicates that the antenna maintains its fundamental monopole performance over the examined frequency range, thereby ensuring reliable signal reception and transmission in multiple directions without significant pattern distortion.

Figure \ref{fig:fig9} illustrates the radiation behaviors of the proposed antenna resonator at various frequencies, including 4 GHz, 6 GHz, 8 GHz, and 10 GHz. The 3D radiation patterns reveal that the antenna consistently delivers effective radiation across the entire frequency range, with notable improvements in gain levels. This performance underscores the role of the metasurface in enhancing the antenna's radiation characteristics. 

\begin{figure}[htbp]
    \centering
    \includegraphics[width=0.48\textwidth]{IMG_2243.jpeg}
    \caption{Radiation behaviors and 3D patterns of the proposed antenna at (a) 4,(b) 6, (c) 8, and (d) 10 GHz.}
    \label{fig:fig9}
\end{figure}

Figure \ref{fig:fig10} presents the radiation and total efficiency characteristics of the metasurface-inspired monopole antenna resonator over the frequency range of 3 GHz to 11 GHz. As depicted, the total efficiency remains well above 80\% across the entire operational bandwidth, indicating robust and stable performance throughout the spectrum. The consistently high efficiency across such a wide frequency range highlights the effectiveness and reliability of the design, making it ideal for a broad range of wireless communication applications. This remarkable efficiency ensures that the antenna performs optimally, meeting the demanding requirements of modern wireless systems [10].


\begin{figure}[htbp]
\centerline{\includegraphics[width=0.45\textwidth]{IMG_2244.jpeg}}
\caption{Radiation efficiency of the proposed antenna.}
\label{fig:fig10}
\end{figure}



\section{Conclusion}
A new metasurface-inspired antenna is introduced and analyzed in this paper, tailored explicitly for UWB applications. The design incorporates a monopole antenna complemented by an 8$\times$8 metasurface. This metasurface comprises compact cells, each featuring four identical star-shaped slots, all constructed on a cost-effective FR4 substrate. 

The integration of the metasurface significantly enhances the antenna's overall performance. The antenna demonstrates effective operation across a broad frequency range, from 3 GHz to beyond 12 GHz, showcasing promising attributes that meet the demanding requirements of UWB systems. It presents a viable solution for modern wireless technologies, offering a balance of efficiency, compactness, and broad bandwidth.



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\end{thebibliography}


\end{document}


