The acoustic field distribution of the deflected wave beam in transmission region from a chirped acoustic grating is described by using Fresnel-Kirchhoff diffraction integral expression. The transmission function of the SAW beam which is diffracted by a linearly chirped grating in Bragg regime is obtained by using quasi-periodicity approximation and this function is considered as the field distribution function in the aperture of the exit plane. It is shown from the analysis that in Fresnel region there is a Fraunhofer plane where the field distribution is the Fourier transformation of the field along the aperture. It is demonstrated that the role played by the grating is two fold i.e. a deflector and a lens. The most important point we found is that the focusing axis of the focused wave beam will translate parallelly when the frequency of the input signal is changed. This scanning configuration is quite different from the traditional deflection scanning. The theoretical predictions are verified by experimental observations and measurements.