Deployment and performance evaluation of a Deployable Rolled-Up Composite SAR Antenna after extended stowage periods

The miniaturisation of spaceborne Synthetic Aperture Radar (SAR) systems requires deployable antennas that can be tightly stowed within CubeSats while maintaining structural and electromagnetic performance after long-term storage. This paper investigates the Deployable Rolled-up Composite Antenna-SAR (DERCA-SAR), a thin-walled glass-fibre composite shell designed to uncoil passively and support a reflectarray surface. Deployment testing after four months of stowage revealed a failure to reach the intended geometry due to material relaxation, with the shell adopting a new monostable coiled state. A modified Lagrangian-based model is proposed to capture this behaviour by redefining the strain energy terms to account for the altered natural geometry. Experimental validation showed that the geometry could be partially recovered by reconditioning the shell. Complementary 3D surface scans quantified normal deformations, with an RMS deviation of 4.34 mm, exceeding the threshold for acceptable radio frequency efficiency losses. Material characterisation across 1.25–5.8 GHz demonstrated significant dielectric loss, yielding low patch antenna efficiencies (9–35%) compared to a commercial substrate. These results highlight the critical trade-offs between mechanical deployability and electromagnetic suitability when using high-strain composites for rollable SAR structures.