Plane-wave reflection from and transmission through a slab of uniaxial anisotropic medium is studied and the concept of ZAP (Zero-Axial-Parameter) medium sheet is defined as the limiting case when the axial parameters and the thickness of the slab vanish simultaneously. It is shown that the ZAP sheet may act as a spatial filter for the incident waves with transmission in a narrow cone around normal direction. Such a sheet may find application in narrowing the radiation beam and reducing sidelobes of an antenna or as a computer privacy filter in optical frequencies.
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doi:10.1109/22.798001