# A Compact Planar Wi-Fi Antenna with Optimized Radiation Patterns for Small UAV Applications
###### Abstract  
This paper proposes a compact planar Wi-Fi antenna with optimized radiation patterns for small uncrewed aerial vehicle (UAV) applications in both urban and open areas. It is suitable for mounting on the outermost side of the non-metallic wing of small UAVs. It has small dimensions of 16.5 mm (L) by 30.3 mm (W) by 1.6 mm (h), and the measured results of its prototype are in agreement with simulated data. Its impedance bandwidths over the two frequency ranges are 2.11 to 2.58 GHz and 5.06 to 7.5 GHz (\(|\)S\({}_{11}\)\(|\leq-10\) dB). At 5.8 GHz, it has stronger radiation below the small UAV to reduce interference from rare-use directions. Its maximum radiations, the directions of the maximum radiation in each elevation plane, are below the UAV and between 14\({}^{o}\) and 29\({}^{o}\) from the horizontal plane. At 2.4 GHz, it has quasi-omnidirectional radiation to ensure a stable link in all directions, and its maximum radiations are near the horizontal plane. The optimized radiation patterns at 5.8 and 2.4 GHz can provide more antenna gain when the small UAV flies farther in urban and open areas, respectively. In addition, it has good vertically polarized radiation for long-distance applications. plinar Wi-Fi antenna; optimized radiation patterns; small UAV; uncrewed aerial vehicle; vertically polarized radiation +
Footnote †  
(PCBs) and batteries, in the UAV body. The UAV takes off from the ground, flies vertically above ground objects, and then flies forward to the farthest position. The flight must avoid hitting ground objects, such as people, trees, and buildings, so the UAV must stay above them. The distance between the UAV and the remote control increases as it takes off from the ground, flies vertically above ground objects, and flies forward to the farthest position. To ensure stable transmission quality and stability, the gain and polarization characteristics of the antenna are determined based on the Friis transmission equation [2]. The antenna must meet the following requirements to reduce interference and provide more antenna gain when the small UAV flies farther in urban areas. First, its \(|\)S\({}_{11}\)\(|\) must be equal to or smaller than \(-10\) dB to ensure efficient power delivery to the antenna. Second, it must have a small size and low profile to meet the portability and aerodynamic requirements for small UAV applications. Third, it must have stronger radiation below the UAV to reduce interference from rare-use directions. Given that the UAV is always above the remote control as it flies away, it is farther away from the remote control than when it was taking off. Fourth, its maximum radiations, the directions of the maximum radiation in each elevation plane, must be below the UAV and between \(10^{\circ}\) and \(30^{\circ}\) from the horizontal plane to provide more antenna gain when the small UAV flies farther in urban areas. Finally, due to the boundary condition of the earth's ground plane, the antenna must have good vertically polarized radiation for long-distance applications. Although many antenna architectures have been proposed [3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14] to meet the requirements for UAV applications, none fully meet the requirements for small UAV applications in urban areas. Due to their small size and lightweight nature, folded dipole antennas have been proposed [3; 4] for small and compact UAV applications, respectively. The fragmented antenna was proposed [3], and its overall dimensions and total mass are \(0.96\lambda_{0}\times 0.8\lambda_{0}\times 0.8\lambda_{0}\) at 240 MHz and 18 g (including the matching circuit). A compact electrically tunable VHF antenna [4] was integrated into the landing gear of a compact UAV with good vertically polarized radiation. However, neither of them has stronger radiation below the UAV, and their maximum radiations are near the horizontal plane.