Recent Advances in Complex Reflectarray Synthesis within the System-by-Design Framework

System-by-Design (SbD) has recently emerged as a powerful and efficient approach in reflectarray antenna (RA) synthesis and optimization. The features/properties of SbD (e.g., its flexibility and natural capability to handle complex multi-scale task-oriented problems) and the intrinsic challenges associated to advanced RA synthesis have motivated a great interest in developing and applying SbD-based approaches in reflectarray engineering. Within this framework, the objective of this contribution is to present a review of the current and most recent advances of SbD formulations as applied to reflectarray design developed at the ELEDIA Research Center. Towards this end, the customization of the SbD loop to the RA synthesis problem is illustrated, and the integration of advanced micro-scale modeling techniques based on learning-by-example strategies with macro-scale task-oriented optimization strategies is discussed. Current challenges and trends in the application of SbD to the solution of advanced RA design problems are remarked, as well.