  We show that a properly designed bianisotropic metasurface placed at the
interface between two arbitrary different media, or coating a dielectric medium
exposed to the air, provides Brewster (reflectionless) transmission at
arbitrary angles and for both the TM and TE polarizations. We present a
rigorous derivation of the corresponding surface susceptibility tensors based
on the Generalized Sheet Transition Conditions (GSTCs), and demonstrate the
system with planar microwave metasurfaces designed for polarization-independent
and azimuth-independent operations. Moreover, we reveal that such a system
leads to the concept of effective refractive media with engineerable impedance.
The proposed bianisotropic metasurfaces provide deeply subwavelength matching
solutions for initially mismatched media, and alternatively lead to the
possibility of on-demand manipulation of the conventional Fresnel coefficients.
The reported generalized Brewster effect represents a fundamental advance in
optical technology, where it may both improve the performance of conventional
components and enable the development of novel devices.
