  Two different methods of the covariant relativistic separable kernel
construction in the Bethe-Salpeter approach are considered. One of them leads
in the center-of-mass system of two particles to the quasipotential equation.
The constructed 4-dimensional covariant functions are used to reproduce
neutron-proton phase shifts for total angular momenta $J=0,1$. Obtained results
are compared with other model calculations.
