# Horizontal Polarized DC Grounded Omnidirectional Antenna for UAV Ground Control Station
## 1 Introduction  
Since the discovery of the interdependency between electrical parameters and electromagnetic radiation, antennas have been developed that actively exploit this phenomenon. Antennas convert electrical parameters (current and voltages) into electromagnetic parameters (electric and magnetic fields) and vice versa. Hence, an antenna can be regarded as a transducer or a sensor as it converts electrical energy to electromagnetic energy, or the opposite [1]. Antennas are always considered essential parts of communication systems, and their radiation and polarization characteristics play a vital role in defining such systems' performance and efficiency [2, 3]. The use of unmanned aerial vehicles (UAVs) is rapidly expanding to commercial, scientific, agricultural, and military applications [4]. To overcome the difficulty of finding the exact location of mobile UAVs from ground control stations (GCS), omnidirectional antennas are utilized to resolve acquisition and pointing complications [5, 6, 7, 8, 9, 10]. It has been proven that using horizontally polarized antennas can achieve a 10 dB improvement in terms of system gain as compared to vertically polarized antennas [11]. For GCS deployment, where the antenna is intended to cover a wide range of angles at variantdistances, it is essential to utilize a low-gain ripple radiation pattern to ensure continuous coverage in the yaw plane (azimuth plane) [12; 13; 14] as gain ripple fluctuates and reduces the coverage range at variant horizontal plane angles [15]. The challenging aspect of designing horizontally polarized omnidirectional antennas is producing a uniform and in-phase current in the antenna's azimuth plane. That necessary condition can be fulfilled by utilizing a single loop or multi-element arrangements [16]. Three primary topological schemes are used with omnidirectional horizontally polarized antennas. In the first topology, a single radiating structure, such as a loop, is utilized to achieve horizontally polarized radiations [17; 18; 19; 20], but it is inherently band-limited due to an open feed. The second group imitates the loop arrangement of first with dipole elements arranged in a ring or circular array format [21; 22; 23; 24; 25; 26] at the expense of a complex open feeding arrangement. The third topology utilizes slots to complete the horizontally polarized antenna. There are a few slot-based omnidirectional antennas described in the literature. In [27], an omnidirectional antenna operating at X band used an array of slot doublets etched in the broadside wall of the rectangular waveguide. However, there was no mention of the azimuth gain, gain fluctuations, and operating band. A slot-based antenna capable of producing horizontal polarization was constructed by arranging alternate slots with opposite tilt angles along the axis with intervals of \(\lambda\)g/2. To improve the antenna's performance, alternate axial slot arrays were shifted by \(\lambda\)g/4 along the axis. Even then, it was not improved by more than \(-7\) dB [28]. In [29], an omnidirectional antenna was proposed, but it was circularly polarized. Moreover, it was not direct-current (DC) grounded and had a built-in main beam frequency scanning problem. In [30], a slant polarized omnidirectional antenna was presented. All slot-based horizontal polarized topologies were arranged in a series of fed axial arrays to achieve the required polarization. The other two methodologies had open feeding networks that interfered with the radiating apertures and perturbed antenna radial symmetry causing an uneven azimuth gain pattern, which further reduced antenna coverage range. This paper proposes an omnidirectional antenna capable of achieving low azimuthal gain variations of \(\pm\)0.5 dB. This work is the first single-element design based on slots capable of horizontal polarization and stable gain without making a complex axial array to achieve the required polarization. The flaunted antenna comprises four slot apertures evenly spaced around the antenna's outer circumference.