High Gain Antennas for Communication between CubeSat and Ground Station

CubeSatellites, often referred to simply as CubeSats, have become game-changers in satellite technology, typically shaped like a cube with each side measuring 10 centimeters (i.e., 1U). CubeSats are a cost-effective and easy-to-use way to engage students in hands-on space projects. Their compact size, and standardized form factors (1U, 2U, 3U, etc.) quickly attracted the attention of the global aerospace industry, researchers, universities and governments. CubeSats have since become platforms for a wide range of scientific, commercial, and educational missions, providing a cost-effective and rapid path to space for a variety of purposes. They are proposed for a variety of applications, such as scientific research, Earth observation, telecommunications and technology demonstrations. Additionally, CubeSats can communicate with each other and form a swarm to perform a wide area measurements and sensing. In order to support all aforementioned capabilities, CubeSats requires high gain, wideband and small antennas for establishing the communication links with each other and with the ground station. However, the limited available space and weight of CubeSats poses significant challenges for any antenna design. These antenna designs need to be small, lightweight while providing good radiation performance (i.e., high gain, and wide bandwidth).

This thesis, therefore, provides the first comprehensive and extensive study of all existing antenna designs that are proposed for CubeSat applications, focusing on proposed and used approaches and techniques to achieve wide bandwidth, high gain, circular polarization and small size. The study focuses on different antenna types with different operating frequency bands. It reviews 49 antenna designs, which include 18 patch antennas, 5 slot antennas, 4 dipole and monopole antennas, 3 reflector antennas, 3 reflectarray antennas, 6 helical antennas, 2 metasurface antennas and 3 millimeter and sub-millimeter wave antennas, 1 inflatable reflector antenna, 1 horn antenna, 2 Yagi-Uda antennas and 1 meanderline antenna. The current CubeSat antenna design challenges and design techniques to address these challenges are discussed. These antennas are classified according to their operating frequency bands, e.g., VHF, UHF, L, S, C, X, Ku, K/Ka, W and mm/sub-mm wave bands and an extensive qualitative comparison is provided. Moreover, the suitability of different antenna types for different applications as well as the future trends for CubeSat antennas are also presented. It was found that microstrip patch, and slot antennas are good candidates for CubeSats as they are cheap, have a low profile, are lightweight, and are easy to fabricate. However, their main limitations are low gain and narrow bandwidth.

Henceforth, this thesis proposes a wideband metal-only F-shaped patch antenna for CubeSats. The proposed antenna consists of an upper patch, a folded ramp-shaped patch and shorting pins connecting the radiating element with the ground plane. The key idea of using the folded patch technique is to generate the second resonant frequency and hence achieve a wide impedance bandwidth. The −10 dB bandwidth is increased. Moreover, three shorting pins are placed between the upper patch and the ground plane to achieve miniaturization and to improve the total gain of the proposed patch antenna. The use of air as substrate leads to very high efficiency. The measured results show that the fabricated prototype achieves a −10 dB bandwidth of 44.9% (1.6–2.7 GHz), a small reflection coefficient of −24.4 dB and a high efficiency, i.e., 85% at 2.45 GHz. The radiation performance of the proposed antenna is measured, showing a peak realized gain of 8.5 dBi with cross polarization level less than −20 dB at 2.45 GHz and a 3 dB gain bandwidth of 61.22%.

This thesis also presents two slot antenna designs: a dual band slot antenna with F-shaped slits for C-band and X-band applications, and a high gain slot antenna with reflector for 2U CubeSat. In the first antenna design, the symmetrical F-shaped slits were embedded to generate an extra resonant frequency and hence improve the antenna bandwidth. The proposed antenna achieved an impedance bandwidth of 500 MHz and a total gain of 5.9 at 5.1 GHz. For the second slot antenna designs, a metallic part of 2U CubeSat’s surface was used as a reflector below the proposed antenna to redirect the back radiation forward. This leads to a substantial suppression of back lobe radiation and hence significant increase of the antenna total gain. The proposed antenna achieved a superior measured gain of 9.1 dBi at 2.7 GHz, reflection coefficient of -21 dB, and an impedance bandwidth of 310 MHz (2.63-2.94 GHz).

Finally, this thesis presents the design and measurement of a compact wide-band Circularly Polarized (CP) monopole antenna for CubeSat applications operating in the X-band.To achieve miniaturization and enhance the radiation performance, the proposed antenna is backed with an Artificial Magnetic Conductor (AMC) Metasurface. It provides a wide -10-dB Impedance Bandwidth (IBW) of 55.12% (6.57–10.98 GHz), and a 3dB Axial Ratio Bandwidth (ARBW) of 23.25% (7.62–9.48 GHz) with a compact size of 0.5λ0×0.5λ0×0.1λ0 at the operating frequency of 8 GHz.