On the Aperture Efficiency of Intelligent Reflecting Surfaces

The concept of intelligent reflecting surfaces (IRS) has recently gained significant attention due to their ability to manipulate the impinging electromagnetic signals and offer anomalous reflections. In this letter, we derive and address the missing piece of prior works, namely the IRS aperture efficiency. Our work provides practical guidelines for selecting the aperture size of the reflecting surface from an antenna designing point of view by taking tapering level into account, and also, revisits the pathloss expression based on a realistic physical model.