Modeling of losses in microstrip reflectarrays based on a simple equivalent circuit approach

Reflection losses of microstrip reflectarray antennas are analytically addressed by approximating the printed structure through a simple equivalent transmission line model. The closed-form expressions of surface impedance (real and imaginary part) are derived through well justified approximations. The compact formulas containing all the degree of freedom of reflectarrays allow efficiently studying the reflection losses. The dependence of the input impedance on the capacitance associated with the printed pattern is highlighted, demonstrating that highly capacitive subwavelength elements are preferable for minimizing reflection losses.