## 3 Antennas with General Aspects Utilized for CubeSat
### Leaky-Wave Antenna (LWA) Technology  
In Ref. [54], a CP microstrip antenna was developed for S-band applications, focusing on ground and intersatellite communication. The antenna measured 80 \(\times\) 180 mm\({}^{2}\) in size. The design used a closed-loop traveling wave as the radiating element to achieve an optimal performance for either LHCP or RHCP. A two-terminal hybrid coupler was employed in the feeding mechanism, enabling control over the phase difference between the feeds. The desired polarization was obtained by feeding the antenna through ports 1 and 2 with equal magnitudes but distinct phase differences. Specifically, a quadrature phase difference of \(-90^{\circ}\) produced RHCP, while a \(+90^{\circ}\) phase difference resulted in LHCP. The simulated reflection coefficient was reported as \(-27\) dB at 2.43 GHz, with a bandwidth of 16.05%. The measurements showed a reflection coefficient of \(-23.5\) dB at 2.52 GHz and a bandwidth of 11.11%. The simulated gain at 2.45 GHz reached 7 dBi, while the measured gain was 5.2 dBi. This antenna design demonstrated adaptability and efficiency for CubeSat communications, effectively balancing compact dimensions with high performance. A higher-order mode suppression technique for single- and dual-frequency microstrip antennas was proposed. The method integrates a microstrip filter within the antenna, simplifying the transmitter/receiver chain by eliminating the need for a separate filter. This technique leads to a higher-order mode suppression of 8 dB using a low-pass microstrip filter without affecting the resonance frequency and the antenna gain. A dual-frequencyantenna for the S- and X-bands was designed using this technique to obtain a bandwidth of 7% and a gain of 8 dBi for the S-band and a bandwidth of 10.5% and a gain of 11.5 dBi for the X-band. This antenna can be used for satellite applications [55]. Reference [56] presents the design of a miniaturized planar Yagi-Uda antenna tailored for integration with PicoSats and other small satellite missions. To address the space constraints inherent in small satellite platforms, the authors employed miniaturization techniques such as meandering and one-dimensional artificial dielectric concepts, effectively reducing the guided wavelength and enabling the antenna to fit within the limited footprint of small satellites. The antenna operates effectively within the frequency range of 3.46 GHz to 3.54 GHz, aligning with communication standards for small satellite missions. Both the simulation and experimental results demonstrate the antenna's high gain and performance, indicating its potential for enhancing data transmission capabilities in CubeSat missions. The study underscores the importance of integrating efficient, low-profile antenna systems to meet the growing demand for high-speed communications with small satellite platforms. Reference [57] introduces a compact substrate-integrated waveguide (SIW) antenna designed for CubeSat applications. This antenna utilized middle-point feeding and shorting walls to achieve broadside radiation at two distinct frequencies, effectively transitioning from a dominant leaky wave at lower frequencies to a more uniform radiation pattern at higher frequencies. The dual-frequency operation enhances communication flexibility, allowing CubeSats to operate across multiple frequency bands. The antenna's compact structure is achieved through shorting walls and middle-point feeding, which reduces the overall size without compromising performance. This design is particularly advantageous for CubeSats with stringent size, weight, and power (SWaP) constraints. The antenna's broadside radiation pattern ensures efficient signal transmission and reception, crucial for maintaining reliable communication links in space. The study demonstrated that the proposed antenna meets the specific requirements of CubeSat missions, offering a viable solution for enhancing communication capabilities in small satellite platforms.