## 3 Antennas with General Aspects Utilized for CubeSat
### Planar Phased Patch Antennas and Their Arrays
dimensions of 100 \(\times\) 100 mm\({}^{2}\). Furthermore, the antenna lacks the ability to beam steer, making it challenging to maintain communication links during CubeSat maneuvers. In the study conducted in Ref. [22], a broad-spectrum, compact stacked-patch antenna was created for communications with a 3U CubeSat. This antenna operates within the S-band range and measures 100 \(\times\) 100 mm\({}^{2}\) in size. A slot-coupled, strip-line feed structure was employed as a key design component. Metallic enclosures surround the uneven strip-line feeding network to enhance the antenna's efficiency. This arrangement is crucial, as it creates a cavity that improves the electric field distribution, strengthening the link between the emitting element and excitation structure through the nearby electromagnetic field. Its gain improved by up to 9 dBi, and the radiation to backward was steered forward. The study reported an extensive 32.6% BW covering the frequency range of 0.8 GHz. This configuration effectively maximizes the CubeSat's available space while ensuring robust satellite communications. The primary drawback of current works that operate in the S-band frequency range is their relatively larger dimensions, especially when they form an array [23]. To resolve this problem, the authors of Ref. [24] developed a foldable microstrip patch antenna featuring a fractal layout for 1U CubeSats. The novel implementation of a Koch snowflake fractal design enabled the antenna's miniaturization while preserving a high gain, low reflection coefficient, extensive bandwidth, and efficient impedance matching. The authors also suggest a simple method for deploying the fractal antenna. The antenna displayed a low reflection coefficient of \(-\)28 dB at 2.3 GHz and offered a wide bandwidth of 28.7%. It attained a moderate gain of 4.39 dBi at the same frequency. The main benefit of this antenna was its compact dimensions, measuring only 60 mm \(\times\) 26.3 mm \(\times\) 0.02 mm. However, its key drawback was its omnidirectional radiation pattern, which leads to reduced gain. In Ref. [25], an array of circularly polarized slot antennas was proposed to facilitate CubeSats communication. The design featured a single-slot array element functioning within the C-band, incorporating four slots and measuring 70.5 mm \(\times\) 23.5 mm. To enhance the radiation efficiency and minimize losses, an SIW structure was implemented, with four slots strategically placed on the upper copper layer. The primary concept involved mounting two SIW slots on both sides of the CubeSat's walls, allowing for sufficient room to integrate solar panels or additional components. This configuration plays a key role in conserving power while directing the antenna beam effectively, ensuring a stable link despite variations in the CubeSat's orientation. The simulated and experimental results demonstrated gains of 5.08 dBi and 4.98 dBi at 5 GHz, respectively. The fabricated antenna exhibited an S\({}_{11}\) of \(-\)17 dB with a limited 1.99% BW. Additionally, the design supports beam-steering capabilities. A cavity-backed slot antenna concept tailored to CubeSat communications is presented in Ref. [26], and it operates in the UHF band (485 and 500 MHz). The design features a looped meander-line slot that wraps around and is affixed to four faces of a 1.5U CubeSat situated between the solar panels. Circular polarization (CP) was achieved by feeding each neighboring loop section with a phase shift of 90\({}^{\circ}\), ensuring reliable signal transmission regardless of the CubeSat's orientation. Additionally, the operational frequency can be tuned for uplinks/downlinks by adjusting the meandered segments' lengths. However, a key limitation of this design is its relatively low gain. In Ref. [27], the authors introduced a dipole antenna set with 3 \(\times\) 1 arrays designed for CubeSat communications (1U). The central objective is to enhance the gain, directionality, and BW while eliminating the need to deploy.