  We present two prescriptions for broadband (~77 - 252 GHz), millimeter-wave
antireflection coatings for cryogenic, sintered polycrystalline aluminum oxide
optics: one for large-format (700 mm diameter) planar and plano-convex
elements, the other for densely packed arrays of quasi-optical elements, in our
case 5 mm diameter half-spheres (called "lenslets"). The coatings comprise
three layers of commercially-available, polytetrafluoroethylene-based,
dielectric sheet material. The lenslet coating is molded to fit the 150 mm
diameter arrays directly while the large-diameter lenses are coated using a
tiled approach. We review the fabrication processes for both prescriptions then
discuss laboratory measurements of their transmittance and reflectance. In
addition, we present the inferred refractive indices and loss tangents for the
coating materials and the aluminum oxide substrate. We find that at 150 GHz and
300 K the large-format coating sample achieves (97 +/- 2)% transmittance and
the lenslet coating sample achieves (94 +/- 3)% transmittance.
