Theoretical Analysis on Reflection Properties of Reflectarray Unit Cells Using Quality Factors

In this paper, a novel theoretical approach to extract the reflection coefficient of reflectarray unit cells is developed. The approach is applied to single-resonance unit cell elements under metallic-waveguide incidence. Using this theory, effects of different physical parameters on reflection properties of unit cells can be thoroughly studied without the need of full-wave simulations. It is shown that the reflectarray unit cell falls into three coupling regions depending on its physical dimensions and substrate properties, which lead to either well-behaved or inadequate reflection phase. Detailed analysis is performed for Ka -band reflectarray unit cells and verified by full-wave simulations. Reflectarray unit cells with different substrate thicknesses, patch widths, and dielectric constants are fabricated and measured. The measurement data closely matches both the theory and full-wave simulations. The presented theory provides valuable physical insight and guidelines for optimization of reflectarray unit cells.