Infrared window materials for modern military aircraft must simultaneously provide adequate optical performance and maintain stringent shielding levels for electromagnetic interference (EMI). Microscopic metal grids deposited on the surface of dielectric windows can provide the conductivity necessary for proper radio frequency or RF shielding. This paper will examine the optical impact of three grid patterns designed for EMI suppression. Transmission blockage and beam diffraction in the far-field have been measured and compared to predicted values. A discussion of durability under severe thermal and rain erosion environments is also included.