  We demonstrate how broadband angular selectivity can be achieved with stacks
of one-dimensionally periodic photonic crystals, each consisting of alternating
isotropic layers and effective anisotropic layers, where each effective
anisotropic layer is constructed from a multilayered metamaterial. We show that
by simply changing the structure of the metamaterials, the selective angle can
be tuned to a broad range of angles; and, by increasing the number of stacks,
the angular transmission window can be made as narrow as desired. As a proof of
principle, we realize the idea experimentally in the microwave regime. The
angular selectivity and tunability we report here can have various applications
such as in directional control of electromagnetic emitters and detectors.
