The Cosmic Microwave Background (CMB) contains a number of faint signals that, if measured, could revolutionize our understandings of the Universe and fundamental physics. Observing these minute signals requires incredible instrumental sensitivity and excellent control over systematic effects. Silicon lenses and sapphire wave plates could play key roles in meeting these requirements if anti-reflection coatings were available to mitigate the large reflections of bare silicon and sapphire. We propose to develop high performance metamaterial antireflection coatings fabricated by machining sub-wavelength structures into the silicon and sapphire surfaces. The proposed coatings are predicted to reduce reflections to below 1% over >3:1 ratio bandwidth with negligible dielectric and scattering loss. This technology will pave the way for improved CMB satellite observatories and could lead to broader use of these imaging technologies in space and for national defense.