High range resolution of radar requires wideband transmitted signals, but the radar transmission of continuous wideband signal is limited by hardware cost and available spectrum resources. When multiple narrow-band signals are used for wideband aggregation, the range side-lobes will increase and the unambiguity range will decrease as the spectral discontinuity and step size of the narrowband signals increase. In order to solve the above problems, a new sparse frequency configuration is proposed, which can obtain equivalent continuous uniform stepped frequency signals through differential processing between sub-bands. Moreover, to make full use of the discontinuous sub-bands with large frequency span, the influence of frequency spans on target scattering characteristics is analyzed and a frequency consistency correction method based on Geometric Theory of Diffraction(GTD) model is proposed. The effects of different frequency spans on wideband aggregation are simulated and analyzed. The possibility of cross-band wideband aggregation is proved. The research of this paper can provide a reference for the backward compatibility of radar systems.