High frequency EM backscatter modeling of large waveguide type geometries is a difficult task. In analysis of radar range profile, wider bandwidths make modeling even more challenging. Here, a new dispersive scattering center model is used based on Model Based Parameter Estimation (MBPE) approach. The model is capable of representing the radar range extension according the nonlinear variations of the scattering phase. A population-based Maximum Likelihood (ML) algorithm is used to calculate the parameters. The PRONY method is used for initialization. Wideband sparse measured frequency domain samples are the inputs of the model. The results are compared with IFFT outcomes.