# Compact UHF Circularly Polarized Multi-Band Quadrifilar Antenna for CubeSat
## 1 Introduction  
The development of the new space industry is disrupting the space market by making satellite fabrication and launch more affordable. Especially miniature satellites, such as the so-called CubeSat [1], enable more accessible access to space. Most of these satellites have dimensions from 1U to 12U and are deployed in a low Earth orbit (LEO) (with U considered as 1 unit with a size of 10 \(\times\) 10 \(\times\) 10 cm\({}^{3}\)). Typical applications of this system are mentioned, such as communication, Earth observation, and space exploration [2; 3; 4]. In the Earth-to-space communication application, thanks to integrating different wireless communication technologies, satellites can connect to terrestrial Internet of Things (IoT) devices in various areas, from the metropolitan zone to the remote zone. In the recent decade, several highly sensitive modulations known as low-power wide-area networks (LP-WAN) have been proposed to enable connectivity from small terminals to space [5; 6]. With long-range connectivity higher than 1000 km, LEO satellites with LP-WAN transceivers based on LoRa ensure the ability to communicate with terrestrial systems [7]. Several companies have successfully implemented satellite systems based on LoRa modulation such as Lacuna Space, Swarm technologies, and Fossa Systems [8; 9; 10]. It confirms that the feasibility will be expanded shortly [11]. A CubeSat includes a communication subsystem for satellite-ground links. The quality of connectivity strongly depends on the antenna system's performance integrated inside the satellite. Antenna design is a challenge for researchers due to the limitations of size, mass, operating frequency, and required bandwidth. In [12; 13; 14; 15; 16], various antenna typesproposed for CubeSat were designed and analyzed, such as monopole, dipole, helical, patch, slot, phase array, reflect array, and metamaterial-based antennas. Regarding operating frequency, antennas operating in a band higher than 1 GHz are often preferred due to their small size and ability to support broadband communications. A wideband patch antenna has been reported that can cover 1.6 to 2.7 GHz with a maximum gain of 8.5 dBi [17]. Due to the linear polarization (LP), the misalignment between the CubeSat and terrestrial station could affect the quality of communication. A circularly polarized (CP) antenna is proposed to solve this problem. In [18], a loaded slot antenna is introduced with a size of 100\(\times\) 100 \(\times\) 1.6 mm\({}^{3}\) and an axial ratio bandwidth of 18.75%. An antenna is designed on low-loss Rogers substrates and provides an omnidirectional radiation pattern with a maximum gain of 8 dBic. On the other hand, directional antennas have also been extensively studied [19; 20; 21; 22; 23; 24; 25; 26]. The article [19] presents a mechanical structure with a horn antenna and reflect array. Due to the 900 elements of coupled loops, the proposal provides a high-gain CP antenna for the K-Band frequency. Some studies suggest using fixed antennas to reduce the risk of deploying mechanical systems in space. The articles [20; 21; 22] propose using feeding networks to distribute signals to radiating elements with suitable phases and then to generate the directional CP pattern. Furthermore, metamaterials are also mentioned in [25; 26]. Differently from the previous examples, sub-GHz bands enable longer transmission distances thanks to the lower path loss and easier obstacle penetration. In article [27], an omnidirectional LP antenna was reported at an operating frequency of 920 MHz. The meander line structure significantly reduced the antenna size with a surface of 50 \(\times\) 80 mm\({}^{2}\) and realized a gain of \(-\)1.8 dB. Another study proposed a slot-based antenna that supports the MIMO scheme mentioned in [28]. Due to the folding of the slot shape, the antenna's resonant frequency band is reduced to 430-510 MHz while maintaining the dimensions within 100 \(\times\) 100 mm\({}^{2}\).