# A Compact Planar Wi-Fi Antenna with Optimized Radiation Patterns for Small UAV Applications
###### Abstract
However, its electrical length of 0.469 \(\lambda_{0}\) is too long for small UAV applications. A compact slot coplanar waveguide-fed antenna [14] was not proposed for small UAV applications and has a very short electrical length of 0.16\(\lambda_{0}\)(L) and a low profile of 0.0128\(\lambda_{0}\)(h) to meet the portability and aerodynamic requirements for small UAV applications. However, it does not have stronger radiation below the UAV, and its maximum radiations are near the horizontal plane. Summarizing the above literature review, most proposed antennas have maximum radiations near the horizontal plane for UAV applications. This feature can meet the requirements for UAV applications in open areas and provide more antenna gain when the small UAV flies farther. The wideband single-sided folded-off-center-fed dipole antenna [13] is the best; it has suitable radiation patterns to meet the requirements for small UAV applications in urban and open areas. In addition, it also has the advantage of a simple and cost-efficient structure, which can make light and small civil UAVs more affordable. However, its electrical length of 0.469 \(\lambda_{0}\) at 3.5 GHz is too long to meet the portability and aerodynamic requirements for small UAV applications. This paper proposes a dual-band antenna with optimized radiation patterns for small UAV applications in urban and open areas. It has a shorter electrical length than the best one proposed: 0.132 \(\lambda_{0}\) at 2.4 GHz [13]. First, this study considers that the small UAV has a camera function and needs to transmit real-time images to the remote control for the user to preview or store. To meet this requirement, Wi-Fi 2.4 GHz and 5.8 GHz were selected as the operating frequencies. Secondly, since many technologies, such as Zigbee and Bluetooth, use 2.4 GHz as the operating frequency [15], there will be more interference at this frequency. Therefore, a quasi-directional radiation pattern was designed at 2.4 GHz, and its maximum radiations are near the horizontal plane for small UAV applications in open areas with less interference, such as mountains, oceans, or farmland. Third, an end-fire radiation pattern was designed at 5.8 GHz for small UAV applications in urban areas. It has stronger and maximum radiations below the UAV and between 14\({}^{\circ}\) and 29\({}^{\circ}\) from the horizontal plane. Finally, to ensure that the characteristics of this antenna will not be significantly affected when applied to small UAVs, the following assumptions are made in this study: First, as shown in Figure 1, the objects around the antenna, such as the UAV wing and propeller, must be made of non-metallic material. Second, the large metal conductors, such as PCBs and batteries, in the UAV body must be located in the far-field region of the proposed antenna. Based on the definition of the far-field region [16], the distance between the small UAV body and the proposed antenna must be \(>\) 46 mm. By performing a theoretical analysis, full-wave simulation, and prototype measurement, we verified that the proposed antenna could meet the requirements for light and small civil UAV applications in urban and open areas. The rest of this paper is as follows: Section 2 presents the antenna design methodology, which includes the structural topology and theoretical analysis. Section 3 presents the parametric studies and full-wave simulations for validating the design theory. Section 4 presents the antenna prototype, measurement setup, comparisons of the simulated data, measured results of the prototype, and discussions about the results. Finally, Section 5 summarizes the results and future work.