SAR imaging can be considered as matched filtration of the signals obtained from different antenna positions. Reference function for such filtration is obtained as a signal from a point-like scatterer placed at the point of interest. Such matched filtration can be described in spectral domain as follows. Relation for a Fourier-harmonic of the received signal from a point-like scatterer can be described as a harmonic of sounding signal with factors which describe its changes due to propagation and backscattering: