  We propose and study, theoretically and experimentally, a new scheme of
excitation of a coherent population trapping resonance for D1 line of alakli
atoms with nuclear spin $I=3/2$ by bichromatic linearly polarized light ({\em
lin}$||${\em lin} field) at the conditions of spectral resolution of the
excited state. The unique properties of this scheme result in a high contrast
of dark resonance for D1 line of $^{87}$Rb.
