## 2 Antenna Design and Configurations  
This section details the design process and arrangement of the antenna. The suggested MIMO LWA was first developed for targeted frequency ranges before being incorporated into a 1U CubeSat with additional cavity layers. The radiation properties of the single-port design were analyzed and then adapted for a dual-port configuration. Performance enhancements, including the impedance bandwidth and isolation, are achieved by engraving nested U-shaped, T-shaped, and S-shaped slots onto the patches and using them as a neutralization system. Furthermore, the antenna's multilayered, stacked construction boosts its gain and radiation efficiency. The nested slots applied to the patches and the space between them reduce unwanted backside and end-fire radiation by leveraging the combined influence of transverse and longitudinal slots, resulting in a broadside radiation pattern that differs from traditional leaky-wave designs. A traditional leaky-wave antenna typically offers end-fire and back-fire radiation patterns, which are not particularly interesting or valuable for CubeSat communication applications, as the metallic walls of the CubeSat may cancel them. Therefore, in our proposed design, we have attempted to make the antenna radiate toward the broadside and outward from the antenna, as well as from the antenna to the CubeSat wall [30]. Figure 1 illustrates the perspective and side views of the proposed antenna before it is integrated into the CubeSat. As illustrated in Figure 1a, the proposed LWA is composed of six layers, each with specific heights (h\({}_{1}\), h\({}_{2}\), h\({}_{3}\), h\({}_{4}\), h\({}_{5}\), and h\({}_{6}\)) and dialectic constants (\(\varepsilon_{1}\) = 10.8, air (\(\varepsilon_{2}\)=1), \(\varepsilon_{3}\) = 2.08, \(\varepsilon_{4}\) = 3.66, \(\varepsilon_{5}\) = 3.66, and \(\varepsilon_{6}\) = 11.2), which will be detailed in the following subsection. Design Principles, Methods, and Techniques  
Figure 2 depicts the individual layers of the suggested dual-port MIMO antenna. The development begins with a single-port configuration, subsequently upgraded to incorporate dual ports. The suggested MIMO LWA utilizes a rectangular patch connected to a transmission line, where one side serves as the input source, and the other is terminated in a 50 \(\Omega\) load. The first phase involves applying fundamental formulas from Ref. [31] to determine the measurements of the rectangular patch and transmission line, thereby customizing the antenna for optimal functionality at 3.8 GHz (with \(\lambda_{0}/2<39\) mm). Not all these well-established equations are not presented in this context and only a few are given here (Equations (1)-(3). \[W=\sfrac{c}{2f_{0}\sqrt{\frac{(\varepsilon_{rf}+1)}{2}}},\sfrac{\varepsilon_{ eff}(\varepsilon_{r}+1)}{2}+\sfrac{(\varepsilon_{r}-1)}{2}\Bigg{(}\sqrt{\left(1+ \left(\frac{12h}{w}\right)\right)}\Bigg{)} \tag{1}\]  
\[\Delta L=0.412\;\mathrm{h}\frac{\left(\varepsilon_{eff}+0.3\right)\left(\frac{ \varpi}{h}+0.264\right)}{\left(\varepsilon_{eff}-0.258\right)\left(\frac{w}{h} +0.8\right)},L_{eff}=\sfrac{c}{2f_{0}\sqrt{\varepsilon_{eff}}},\;\mathrm{L}=L _{eff}-2\Delta,\;\;L_{g}=L+(6h) \tag{2}\]  
\[W_{g}=W+(6h) \tag{3}\]  
After considering all the principles and equations of conventional and leaky-wave antennas, it should be noted that altering the antenna dimension to a larger and smaller size can shift the band to lower and higher bands. The leaky-wave configuration prioritizes strong directivity, a high gain, a low loss, and a simple structure. LWAs are classified as traveling-wave antennas, characterized by a wave propagating along an elongated framework regarding the wavelength. This feature generates currents along the antenna's length, leading to end-fire and back-fire radiation patterns influenced by the open-stopband (OSB) effect, as noted in Refs. [32; 33].