## 1 Introduction  
Even though it is described as the golden age of SAR satellites, this era presents challenges in terms of the need to minimize spacecraft size to economize the overall system cost. In order to achieve an affordable small satellite system, mass and size reduction are important. Furthermore, operating a SAR constellation might involve shared or multiple orbits. Reducing a satellite's size imposes constraints on the SAR antenna size, system design, and satellite subsystems, due to the high-power demands of a SAR mission. Trade-offs must be made between the SAR parameters and the orbital considerations in order to enable a small satellite to perform the same functions as heavier and larger satellites. This paper explores the design considerations for micro-sized SAR satellites, focusing on two main challenges: the high-power consumption of the payload and the antenna area requirements in terms of the SAR system. The evolution of space-based microwave remote sensing includes prominent missions such as SEAST [1], ERS1/2, J-ERS-1 [2; 3; 4], SIR-C/X SAR [5], and Radarsat-1 [6], which marked the early era of spaceborne SARs. The field has since advanced with SAR satellite constellations like TerraSAR-X [7; 8], COSMO-SkyMed [9], Radarsat-2 [10; 11], PAZ [12; 13],Sentinel-1 a/b [14; 15; 16; 17], ALOS-2 [18; 19], and Geofen-3 [20; 21]. Recent developments have seen a remarkable reduction in satellite mass, as exemplified by contemporary micro-sized SAR satellites like ICEYE [22], Capella [23; 24; 25; 26], StriX-a [27], QPS SAR [28], S-STEP [29], HISEA-1 [30; 31], and Umbra [32]. To compare these missions, a summary of their fundamental parameters, for evaluating the input and output parameters, is provided in Table 1.  
The selection of the relevant band is associated with the observed target. The selection of the operating frequency band for a spaceborne SAR satellite is influenced by various factors, including system performance, mission requirements, and technical considerations. While the X-band, in recent years, has been a commonly used frequency band for spaceborne SARs, prior to this, the L-band and C-band frequency bands were also utilized for SAR applications. The optimal altitude range for SAR satellites is typically determined based on a trade-off between the spatial resolution, coverage area, revisit time, signal strength, surface penetration, and mission-specific requirements. The selection of the altitude involves considering the specific objectives of the mission, the target applications, and the technical capabilities and limitations of the satellite platform. Additionally, factors such as regulatory requirements, collision avoidance with other satellites and space debris, and compatibility with other satellite constellations or Earth observation missions may also influence the choice of altitude. The specific mission requirements and objectives should ultimately guide the selection of the optimal incidence angle interval for the SAR satellite. The antenna length and width should be carefully optimized to achieve the desired swath  
coverage, resolution, and gain, while also considering factors such as the available mass constraints and its integration with the satellite platform. In practice, the antenna dimensions for a SAR system can vary significantly, based on the specific mission requirements and the chosen antenna design. The length and width of the antenna are usually determined through a trade-off analysis that considers the desired imaging performance, the available resources, and the technical constraints. Overall, antenna sizing for a small spaceborne SAR satellite involves optimizing parameters such as the frequency, beamwidth, resolution, swath coverage, pulse reputation frequency (PRF), system losses, transmitting power, and the need to meet mass and volume constraints. The balance of these factors needs to be considered in order to achieve the desired imaging performance, while taking into account the limitations of the small satellite platform.