# Metasurface Source Antenna Gain Improvement Using Simple Side Metal Structure
## 1 Introduction
Further optimization, by applying two metallic plates to a \(4\times 1\) patch array, resulted in a significant gain improvement to 16.8 dBi, showing an overall gain increase of about 7 dBi. This enhancement also enabled better control over the direction of the radiation waves. Another study [33] explored gain enhancement by applying a radiator structure through stacking to a patch antenna. In this approach, a radiator structure was applied to a single antenna element using a stacked 2 \(\times\) 2 array of patches. This design was based on the principle of a double H-type slot microstrip patch antenna and utilized a combination of coplanar parasitic radiators and radiating patch structures to create a resonant cavity. This structure helped reduce the Q factor and increased the antenna's bandwidth, thereby improving performance. Despite these advancements, using a fundamentally low-gain source antenna, such as a patch antenna, on a metasurface imposes limits on the gain and aperture efficiency of the transmitted wave. To address these limitations, a sidewall structure can be employed. For instance, A PEC (Perfect Electric Conductor) sidewall was used to surround a TA composed of four layers [18]. This configuration resulted in a gain improvement of 1.9 dBi compared to the absence of a sidewall. Additionally, the aperture efficiency was significantly enhanced from 36% to 56%. This approach is based on the principle of using a reflector structure, one of the effective methods for improving the gain of patch antennas. In studies focused on improving the gain of patch antennas, it is often found that the existing gain is insufficient or that complex designs are needed to achieve the desired performance levels. To effectively use a patch antenna as a source for a TA, it is crucial to develop a structure that not only enhances gain but also allows for precise control over the waveform of the radiated waves. Simplifying the design of both the source antenna and unit cell structures is essential for achieving cost advantages, which is a key focus in metasurface research. To address these challenges, this study proposes a novel gain enhancement method by applying a simple metallic structure to a single patch antenna. In our approach, a TA is designed using a patch antenna with improved gain as the feed source, consisting of four layers of metallic cross-slot unit cells optimized to operate at 9 GHz. This study aims to simplify the source antenna design while enhancing performance, aligning with the goals of cost efficiency and effective metasurface application. The paper is organized into three sections: Section 1 introduces the patch antenna design and gain improvement method; Section 2 discusses the design of the unit cells and the overall TA configuration for 9 GHz operation; and Section 3 presents an analysis of the beam pattern and gain performance of the TA using the enhanced patch antenna. In this study, a patch antenna operating at 9 GHz is designed, and both simulation and actual measurement results of its performance, using a side metal structure to improve gain, are examined. The proposed side metal structure includes a metallic sidewall surrounding the source antenna and a metallic side plate that integrates with the patch antenna to increase the intensity of radiated waves. For the basic analysis of the proposed side metal structure, certain efficiency losses of the antenna are not considered when assessing the gain. This innovative design aims to balance improved performance with structural simplicity, facilitating more effective and cost-efficient metasurface applications.