# Compact Beam-Scanning Reflectarray Antenna with SLL Reduction Using In-Plane Panel Translations
## 1 Introduction  
Modern low Earth orbit (LEO) satellite communication systems are reshaping broadband connectivity by providing global coverage with reduced latency compared to traditional geostationary (GEO) high-throughput satellites (HTSs). These systems offer greater flexibility and scalability by relying on gradually deployable and expandable constellations of smaller satellites [1]. LEO constellations require highly flexible user terminals capable of continuous beam tracking to maintain seamless connectivity with fast-moving satellites. Small phased arrays are often used to achieve this reconfigurability, as traditional parabolic reflector antennas cannot provide the wide-angle scanning required for this application [2]. However, these terminals face particularly stringent cost requirements to allow mass adoption, and thus, reducing their complexity is a major priority [3].  
Spatially fed arrays (SFAs) are positioned as a competitive solution for modern reconfigurable mm-wave terminals. Low manufacturing costs are enabled by mature PCB [4, 5, 6] or 3D-printing [7, 8, 9] technologies for the array elements. Furthermore, the use of low-profile planar surfaces allows for easy stowage and integration to various platforms [10, 11]. Electronically reconfigurable antennas can be achieved by introducing active componentsto the array elements, e.g., via integrated electronics [12; 13; 14] or MEMS [15; 16]. These however add costly components and control circuitry, sacrificing part of the simplicity and affordability of SFAs. Alternatively, multiple feeding elements can be used to illuminate a passive SFA, each one steering the beam in a different direction. Beam switching can then be used to steer the beam, at the expense of complex feeding configurations and antenna optics [17; 18; 19].  
Mechanical beam steering is a more accessible option that relies on translations and rotations of the feed or panel, trading mechanical complexity and lower aperture efficiency for affordability and a simpler control system with a significantly lower power consumption. Some implementations based on Risley prisms use two co-axially rotating surfaces to achieve 2D steering at the expense of the complexity and losses of two SFAs [20; 21; 22]. One-dimensional wide-angle steering can be achieved by moving the feed along a focal arc while pointed towards a fixed point on the aperture [23; 24; 25; 26]. Another common approach that prioritizes mechanical simplicity relies on linear panel translations to achieve 1D steering [9; 27], avoiding movements and re-orientations of the feeding RF chain. This improves the long-term reliability of the system at the cost of requiring a larger antenna volume to support the movements of the panel.  
This work presents a compact and cost-effective RA antenna capable of 1D beam scanning in the Ka band. In-plane panel translations are used to steer the beam. This scanning approach excels in mechanical simplicity, requiring only a light rail-mounted panel controlled by a low-power motor. An iterative process is used to design the phase response of the RA, progressively expanding its steering range while controlling its scan losses. At every iteration, the radiation requirements are updated and the phase response of the RA is adjusted using a multi-focal optimization algorithm. Once a range of 45 degrees is achieved, a novel technique is proposed to reduce the SLLs. The phase response is refined to avoid partially collimating phase patterns in the directions where the highest side lobes are predicted, achieving an estimated reduction in maximum SLL of 2.3 dB. Despite having an \(F/D\) of only 0.47, the antenna achieves a low measured scan loss of 1.1 dB and a moderate gain of 31.6 dBi at 29.5 GHz.