## 3 Design and Geometry of the Proposed Antenna  
### S-Band Antenna Design  
In order to enhance communication capabilities for the satellite-ground link without compromising the already qualified payload, a lightweight, flat, wideband, and compact S-band antenna is required. The requirements that the S-Band antenna must meet are defined in Table 1.  
In addition, due to the special environment in space and the requirements of the ANSER program, the antenna design has many other environmental challenges to consider [8; 9]:  
* The antenna must be mechanically robust and able to survive both random vibration and shock during the launch. The thermal design of the antennas must be carefully evaluated; therefore, antennas are designed to perform over a wide temperature variation, from \(-\)50 \({}^{\circ}\)C to +90 \({}^{\circ}\)C.
* In addition, materials for the antenna need to be chosen carefully, considering the effects of vacuum and micro-gravity without losing sight of EMC and mutual coupling amongst the payloads, circuits, and other antennas fitted in a small space. * A major consideration for antenna design is the interaction between antennas and the modem CubeSat structures. The spacecraft's structure can cause electromagnetic scattering, as well as have blockage effects on the antenna's radiation patterns. The scattering can interfere with the antenna's radiation pattern and can cause severe degradation in gain performance and sidelobes. This degradation will have a major influence on the communication-link system's performance and needs to be assessed. For that reason, a study was conducted on the most suitable positions to place the antenna in terms of link budget and coverage (Figure 2). Taking all this into account, a multilayer microstrip antenna has been designed, developed, integrated, and measured. The choice of microstrip technology is based on the advantages such as being lightweight, low-profile, cost-effective, and flexible for integration, which is particularly crucial in space applications. Microstrip antennas can be used either as single elements when the gain requirements are low or in an array configuration such as microstrip patch antenna arrays, phased arrays, or reflect arrays in order to boost their gain, beamforming, and beam scanning performance [12]. However, the main limitation of microstrip patch antennas (MPAs) is their narrowband characteristics due to their high Q nature [14; 16]. A number of wideband approaches have been proposed to enhance the impedance bandwidth of microstrip patch antennas, such as the use of shorting pins or walls [17; 18], parasitic elements attached either to the radiating or non-radiating edge of the patch [19; 20], stacked multiple patches on different substrate layers [21], aperture-coupled feeding techniques [22; 23; 24], metamaterial-based antennas and increasing the substrate \begin{table}
\begin{tabular}{c c} \hline Frequency & 2.03 GHz \(\pm\) 10 MHz and 2.205 GHz \(\pm\) 25 MHz \\ \hline Reflection coefficient & \(\leq\)\(-\)12 dB \\ \hline Gain & \(\geq\)\(-\)10 dBi \\ \hline Polarization & Circular dual \\ \hline Axial ratio & \(<\)4 dB \\ \hline Maximum size & 80 \(\times\) 80 mm \\ \hline Maximum height & 6.6 mm \\ \hline Connector & SMP \\ \hline \end{tabular}
\end{table} 
Table 1: S-Band antenna requirements. thickness relative to the free space wavelength or using substrates with dielectric constants close to unity. However, when using any of the aforementioned techniques, a trade-off must be performed between the bandwidth performance of the antenna and its radiating characteristics [9; 14; 16; 25; 26]. Despite that, in this work, a wideband S-band multilayer antenna has been developed, qualified, and integrated for Leader-S satellite, maintaining optimal radiation characteristics. In addition, the unique environment of space and the requirements of the ANSER program impose numerous environmental challenges on antenna design [8; 9].