  Intelligent reflecting surfaces can improve the communication between a
source and a destination. The surface contains metamaterial that is configured
to "reflect" the incident wave from the source towards the destination. Two
incompatible pathloss models have been used in prior work. In this letter, we
derive the far-field pathloss using physical optics techniques and explain why
the surface consists of many elements that individually act as diffuse
scatterers but can jointly beamform the signal in a desired direction with a
certain beamwidth. We disprove one of the previously conjectured pathloss
models.
