## 4 Lunar Antenna Types
### Wire Antennas
#### 4.4.4. Sleeve Dipole Antennas  
The final classification within the category of wire antennas is the sleeve dipole antenna. One of the main characteristics of sleeve dipole antennas is the simplicity of alignment between the transmitter and receiver antennas to ensure polarization matching. This antenna consists of a pair of radiation elements in the form of arms. The upper arm takes the shape of a coaxial copper cylinder, whereas the lower arm is composed of two components: a copper sleeve-shaped cylinder and an inner coaxial feeding line. The feeding is facilitated by a semi-rigid coaxial wire that passes through the lower arm, effectively linking the upper and lower sleeve arms [79]. The sleeve dipole design enables end-feeding of the antenna, eliminating cable and feed-point interactions that can disrupt its performance. The antenna itself is a balanced structure, making it compatible with unbalanced coaxial lines and eliminating the need for an additional balun for feeding. Furthermore, the sleeve antenna maintains consistent performance regardless of environmental conditions. These attributes render it well-suited to applications in radar, radio communication, and wireless technology. In [17], the study delves into the analysis of the antenna performance on the Rashid rover situated within Atlas Crater. The sleeve dipole antenna was chosen for its exceptional thermal stability, which permits the application of various coatings without impacting the antenna's parameters. Figure 16 provides an overview of the sleeve dipole antenna design implemented in the Rashid rover mission. This design permits the application of various thermal coatings while preserving optimal performance. To mitigate the impact of the moon's extreme surface temperatures, which result from the lack of an atmosphere and may pose challenges to an antenna's functionality and reliability, it is essential to thoroughly investigate these effects before initiating a mission. The antenna underwent simulations and optimizations within CST Microwave Studio (Version 2023), integrating it seamlessly into the Rashid rover. These simulations incorporated a lunar ground model mimicking the properties found in Atlas Crater. Accounting for the lunar regolith's effects in electromagnetic simulations is crucial as it has been observed that this lossy ground can significantly affect antenna performance, particularly at higher frequencies. The average permittivity of lunar soil was determined to be 3, as referenced in [80; 81; 82; 83]. Within the lunar environment, the antenna demonstrated a gain of 2.3 dB across a bandwidth ranging from 2.3 GHz to 2.7 GHz. Notably, the lunar ground, functioning as both a partial reflector and an absorber of electromagnetic waves, introduced multiple ripples to the antenna pattern due to ground reflections [84; 85]. For a comprehensive comparison of various wire antennas, including their applications, performance characteristics, and simulation parameters, please refer to Tables 10 and 11. Figure 15: The structure of the CH2 antenna. Adopted from Lunar Penetrating Radar onboard the Chang’e-3 mission by [PERSON] et al., Research in astronomy and astrophysics (2014) [75]. Reproduced by permission of RAA. All rights reserved. Based on the antennas employed in actual missions and the literature available, Table 12 provides a summary of recommended frequencies in lunar communication and their respective applications [86].