# A Wideband Metal-Only Patch Antenna for CubeSat
## 1 Introduction  
Cube Satellites (CubeSats) are a class of tiny satellites that have become popular space programs and have opened the door for universities and small companies to gain experience in space technology using cost-effective missions [1]. CubeSats operate at Low Earth Orbit (LEO) at altitudes of 200 km to 800 km, have a mass ranging from 1.3 kg to 6 kg and total volumes of 10 cm \(\times\) 10 cm \(\times\) 10 cm (1 U), 10 cm \(\times\) 10 cm \(\times\) 20 cm (2 U) and 10 cm \(\times\) 10 cm \(\times\) 30 cm (3 U) [2]. Compared with conventional, medium and mini sized satellites, CubeSats have lower mass, are cheaper and are easier to fabricate. A critical component of CubeSat' telecommunication subsystem that is responsible for establishing the communication link between CubeSats and ground stations is the antenna. Because of the limited real estate of CubeSats, antenna designs must meet the size restriction of CubeSats while yielding high gains and wide bandwidths [3]. Moreover, designed antennas for CubeSats must have a low profile to occupy a small area on CubeSat's surface, thus maximizing the space dedicated to solar panels. The aforementioned challenges can be addressed using patch antenna designs because they have a low profile and are lightweight and cheap. In addition, they have low radiation loss, easy matching of input impedance and are easily integrated with electronic devices [4]. However, their main limitation is their narrow bandwidth, low gains and low efficiency at S-band, i.e., 2.40 GHz [5, 6, 7]. For example, in [8], the authors presented S-band transparent mesh patch antenna for 3 U CubeSat. The proposed antenna has a low profile (28.44 mm \(\times\) 43.7 mm) and an efficiency of 85.9%. However, its main limitation is its narrow \(-10\) dB bandwidth, i.e., 1.67%, and a low gain, 5.3 dBi. Moreover, the authors of [9] proposed a meshed patch antenna thatoperates at 2.45 GHz for small satellites. The proposed antenna is integrated with solar cells and fed by two orthogonal feeding ports to achieve circular polarization. It has a small size of 24.1 mm \(\times\) 24.8 mm, and hence, provides more space for solar cells. Its main limitations are the narrow bandwidth (2.65%) and low gain (4.8 dBi). Another S-band transparent meshed patch antenna is presented in [10]. To improve the antenna's gain and bandwidth, the authors used three transparent meshed patch configurations on CubeSat's surface, which uses the same feeding line. They reported a high gain, of 7.2 dBi, and bandwidth, of 2.65%. Its main limitation, however, is the large antenna size, i.e., 100 mm \(\times\) 100 mm. In [11], [PERSON] et al. designed a meshed patch antenna for CubeSat applications. The ground plane is made of metamaterial with Reactive Impedance Surface (RIS). This is important as it enhances the bandwidth. The proposed antenna operates at 2.25 GHz and provides a wide bandwidth of 11.1%. However, it has a large antenna size (100 mm \(\times\) 100 mm) and provides a low gain, of 4.87 dBi. To address the bandwidth limitation of patch antennas while maintaining a compact size, several techniques have been proposed, such as introducing slots, with popular shapes being the E- and U-shaped patches [12; 13; 14; 15] and using shorting pins or walls [16; 17; 18]. In addition, by using thick substrates along with the folded patch feeding technique, the impedance bandwidth of patch antennas can be greatly increased [19]. The authors of [12] proposed an E-shaped patch antenna. They placed 25 mm \(\times\) 27.7 mm asymmetric patch above the ground plane with air substrate between them. The antenna was fed by a folded shaped probe that has unequal arms. They reported a measured impedance bandwidth of 19.8% with an operating frequency of 2.378 GHz. Another E-shaped antenna implementation on a 140 mm \(\times\) 210 mm ground plane was reported in [13]. The position, the width and the length of the slots was studied to provide an optimal impedance bandwidth of 30.3% at 2.4 GHz using probe feeding and air as substrate material.