  Within a covariant Bethe-Salpeter approach the relativistic complex separable
kernel of the neutron-proton interaction for the coupled $^3S_1^+$-$^3D_1^+$
partial-wave state is constructed. The rank-six separable potential elaborated
earlier is real-valued, and therefore makes it possible to describe only the
elastic part (phase shifts, low-energy parameters, deuteron properties, etc.)
of the elastic neutron-proton scattering. The description of the inelasticity
parameter comes out of the imaginary part introduced intthe potential. The
complex potential parameters are obtained using the available elastic
neutron-proton scattering experimental data up to 1.1 GeV.
