  In this paper we consider a robust identification problem for a linear
dynamical control system with limited-frequency intervals. In mathematical
terms, this is the problem of recovering functions in Hardy spaces. Our purpose
is to bound Patil's approximants in the upper half plane case, out of a bounded
real interval $I$. To this end, we deal with residu techniques and give a class
of functions to provide boundedness of these approximants on the complement of
this interval.
