We study the decay properties of Wigner kernels for Fourier integral operators of types I and II. The symbol spaces that allow a nice decay of these kernels are the Shubin classes \(\Gamma ^m({\mathbb {R}^{2d}})\) , with negative order m. The phases considered are the so-called tame ones, which appear in the Schrödinger propagators. The related canonical transformations are allowed to be nonlinear. It is the nonlinearity of these transformations that are the main obstacles for nice kernel localizations when symbols are taken in the Hörmander’s class \(S^{0}_{0,0}({\mathbb {R}^{2d}})\) . Here we prove that Shubin classes overcome this problem and allow a nice kernel localization, which improves with the decreasing of the order m.
