## 4 Conclusions  
The novel miniaturized circular polarized dual-port MTS-based leaky-wave MIMO antenna presented in this study represents a significant advancement in CubeSat communication technology. It has a small size of 40 \(\times\) 30 mm\({}^{2}\), operating at 3.75-5.25 GHz, 6.4-15.4 GHz, and 22.5-30 GHz, allowing it to meet the size limitations of CubeSats for space missions. It can also offer reliable long-distance communication, especially for LEO, with its limited-power condition, as it achieves a high gain and efficiency of 12.5 dBi and 85%, respectively. The proposed antenna was designed primarily for low-power CubeSat communication systems, which typically operate at modest transmit power levels (e.g., 0.5-2 W) due to tight power budgets in space platforms. With such high radiation efficiency, the vast majority of the input power is effectively converted into radiated energy, minimizing wasted energy as heat or surface wave losses. This directly reduces the power that must be drawn from CubeSat's limited onboard energy supply to meet link budget requirements. In addition to the positive effect of having high efficiency, the high directive gain of the antenna provides a focused energy towards the target, reducing high-power transmission as well as signal dispersion. The low-profile, lightweight design also facilitates thermal management, as it avoids bulky structures that can trap heat or require active cooling. Regarding power handling and nonlinearity, the antenna was constructed from linear, passive materials that do not exhibit nonlinear behavior within the typical CubeSat operating power range. Given the passive MTS and the absence of active components in the antenna structure, nonlinearity or RF breakdown is not expected under standard operational conditions. However, should higher power applications be pursued, material breakdown thresholds and thermal effects could be investigated further.  
The flower-like MTS, composed of coffee bean-shaped arrays and integrated with substrates of varying permittivity, enables precise control of electromagnetic waves, resulting in efficient leaky-wave propagation and beamsteering capabilities without the need for mechanical components. This design reduces complexity and weight while enhancing mission flexibility by allowing frequency- or phase-dependent beamsteering for the dynamic tracking of ground stations or inter-satellite links. Moreover, since the demand for higher data rates is growing in applications such as Earth observations and inter-satellite communications, the dual-port configuration of the proposed MIMO antenna is beneficial. The proposed antenna's CP feature enhances signal integrity, even in the presence of misalignment issues in CubeSat missions. Therefore, all these characteristics make the proposed antenna a high-performance candidate for CubeSat communications, especially for LEO.  
T.S. designed the antenna, carried out the measurements, and wrote the first draft of this paper. S.K. and S.S. evaluated the findings and edited the first draft of this paper. All authors have read and agreed to the published version of the manuscript.  
This work has been jointly supported by the European Space Agency, under contract number: 4000145253, and by Silicon Austria Labs (SAL), owned by the Republic of Austria, the Styrian Business Promotion Agency (SFG), the Federal State of Carinthia, Upper Austrian Research (UAR), and the Austrian Association for the Electric and Electronics Industry (FEEI).  
All the required data are within the main text.  
The authors thank the ESA, SAL, and WiSAR Lab (ATU, Donegal) for supporting this investigation and experimental assessment.  
The authors declare no conflicts of interest.