  Coronagraphy is an efficient technique for identifying and characterizing
extra-solar planets orbiting in the habitable zone of their parent star. An
important family of coronagraphs is based on amplitude or phase filters placed
at an intermediate image plane of the optical system, spreading starlight
outside of the so-called Lyot stop located at the exit pupil plane of the
instrument. This article explores the potential of circular amplitude and phase
gratings employed as image plane coronagraph filters. It presents a theoretical
analysis of the simplest case of an amplitude circular grating and introduces
an inversion paradigm with respect to classical Lyot coronagraph, by exchanging
its image and pupil masks. Various types of circular gratings are considered
and their performance is evaluated with the help of numerical simulations. The
most promising solutions are presented. We conclude that high attenuation
ratios of the starlight are feasible, provided that the system has been
carefully optimized
