The application of ferroelectric thin films for the development of frequency and phase agile microwave components has been the reason behind very encouraging demonstrations of tunable microwave devices in recent years. Thus, one could conclude with basically a general consensus, that the question of the suitability of thin film ferroelectric technology for the fabrication of superior tunable microwave components has been already answered in a favorable way. However, what is still pending in regards to the validation of this technology is the development of evaluation methodologies to set forth the standards for the material quality and subsequent performance criteria of specific components and devices based on this technology. In this paper we discuss the evaluation methodology under implementation at NASA Glenn Research Center aimed at identifying and optimizing the most relevant parameters of BaxSr1−xTiO3 (BSTO) ferroelectric thin films (i.e., tunability, losses, thickness, crystalline quality, etc.) as defined by a specific microwave application (in our case, phase shifters for reflectarray antennas). Results of our material analysis based on X-ray diffraction and ellipsometry, and how these properties correlate with RF performance for a targeted circuit, will be presented.