  Using stereographic projection approach we develop a theory for calculation
of dynamical susceptibility tensor of Skyrmion crystals (SkX), formed in thin
ferromagnetic films with Dzyaloshinskii-Moriya interaction and in the external
magnetic field. Staying whenever possible within analytical framework, we
employ the model anzats for static SkX configuration and discuss small
fluctuations around it. The obtained formulas are numerically analyzed in the
important case of uniform susceptibility, accessible in magnetic resonance (MR)
experiments. We show that, in addition to three characteristic MR frequencies
discussed earlier both theoretically and experimentally, one should also expect
several resonances of smaller amplitude at somewhat higher frequencies.
