Development of a deployable Synthetic Aperture Radar antenna for a nanosatellite conceptual design

Abstract

For a real-time maritime surveillance application in the extended territorial waters of New Zealand, this work aims to develop a viable concept design for a deployable Synthetic Aperture Radar (SAR) antenna to fit in a CubeSat design space. To trade off a large antenna aperture, which is essential to enhance SAR performance, and a high packaging efficiency, potentially ≤ 12U, a 4 m x 0.3 m reflectarray with a stiff-and-flexible and novel passive deployable system is selected as the most promising solution for this application. A High Strain Composite (HSC) structure with a shallow “tape-measure” inspired shape is presented to support the SAR reflectarray and compactly stow it through a rollable deployment system. The release of the elastic energy stored in the coiled structure will enable the deployment, and the structural stiffness will be provided by a boundary condition that maintains the naturally curved cross-section during stowage. With this design constraint, the transition zone (ploy region) that develops between the stowed and deployed state may significantly impact the stowage capabilities. The elastic behaviour of the structure will be analytically studied in terms of the change of curvatures and bending stiffness as they dominate the deformed shape in the coiling process. Existing analytical models that predict the ploy regions are considered to estimate the natural ploy length and the equivalent coil diameter. Finite Element (FE) models are developed to compare the analytical models and explore the stress field generated within the ploy region when the length of this region is forced to be shorter than the natural ploy length. FE model observations and data are also used to improve the analytical model that describes the deformed shape by imposing non-uniform boundary conditions on the curvatures’ field distribution within the ploy region.