  We introduce the first conceptual design of a free-space thin-sheet isolator
with unlimited aperture and the possibility of a broadband omnidirectional
rejection of the backward propagating light. The proposed design involves a
multilayered resonant cavity incorporating subwavelength magnetic layers,
dichroic nanolayers, and an optional metallic nanolayer. The cavity resonance
enhances the Faraday rotation produced by the subwavelength magnetic layers,
while providing nearly total absorption of the backward-propagating light by
the dichroic nanolayers. The latter is a necessary and the most challenging
condition for a thin-sheet isolator with unlimited aperture to function. The
(optional) metallic nanolayer provides rejection of the obliquely incident
light, which otherwise would be partially transmitted in either direction. Our
numerical simulations and quasi-optical measurements at millimeter-wave
frequencies illustrate how the key elements of the layered-sheet isolator work.
Our approach can be scaled down to long- and mid-infrared wavelengths.
