  We study the dynamical properties of an electron gas scattered by
impenetrable antidots in the presence of a strong magnetic field. We find that
the lineshape of the cyclotron resonance is very different from the Lorentzian
and is not characterized by the Drude scattering rate. We show that the
dissipative dynamical response of skipping orbits, $S_c(\omega)$, is broadened
on a scale of the cyclotron frequency $\omega_c$ and has a sharp dip $\propto
|\omega-\omega_c|$. For small antidots, $S_c(\omega)$ is strongly modulated
with a period equal to $\omega_c$ and has sharp square-root singularities for a
series of resonant frequencies. For large antidots, $S_c(\omega)$ has a hard
gap at $\omega<\omega_c$ between two sharp peaks, associated respectively with
edge states and free cyclotron orbits.
