  Applying numerical modeling coupled with experiments, we investigate the
properties of wideband resonant reflectors under fully conical light incidence.
We show that the wave vectors pertinent to resonant first-order diffraction
under fully conical mounting vary less with incident angle than those
associated with reflectors in classical mounting. Therefore, as the evanescent
diffracted waves drive the leaky modes responsible for the resonance effects,
fully-conical mounting imbues reflectors with larger angular tolerance than
their classical counterparts. We quantify the angular-spectral performance of
representative resonant wideband reflectors in conic and classic mounts by
numerical calculations with improved spectra found for fully conic incidence.
Moreover, these predictions are verified experimentally for wideband reflectors
fashioned in crystalline and amorphous silicon in distinct spectral regions
spanning the 1200-1600-nm and 1600-2400-nm spectral bands. These results will
be useful in various applications demanding wideband reflectors that are
efficient and materially sparse.
