  SuperAGILE is the X-ray stage of the AGILE gamma-ray mission. It is devoted
to monitor X-ray (10-40 keV) sources with a sensitivity better than 10 mCrabs
in 50 ks and to detect X-ray transients in a field of view of 1.8 sr, well
matched to that of the gamma-ray tracker, with few arc-minutes position
resolution and better than 5 us timing resolution. SuperAGILE is designed to
exploit one additional layer of four Si microstrip detectors placed on top of
the AGILE tracker, and a system of four mutually orthogonal one-dimensional
coded masks to encode the X-ray sky. The total geometric area is 1444 cm^2. Low
noise electronics based on ASIC technology composes the front-end read out. We
present here the instrumental and astrophysical performances of SuperAGILE as
derived by analytical calculations, Monte Carlo simulations and experimental
tests on a prototype of the silicon microstrip detector and front-end
electronics.
