Inverse scattering and imaging of compensated compact ranges by plane wave analysis

The Compensated Compact Range (CCR) 75/60 of Airbus DS GmbH has been analysed to gain insight into its scattering behaviour. To achieve this aim, an approach based on the plane wave spectrum representation combined with inverse scattering and imaging techniques is proposed. The proposed approach firstly computes the plane wave spectrum of the scattered field from the main reflector by using the two dimensional Fast Fourier Transformation (FFT). Then, the individual plane wave fields are back propagated to the reflectors. By considering the geometrical shape of the curved reflectors, the total field distribution on the reflectors is imaged by using the spectrum. The main and sub reflector are designed to fulfill the Mizugutch criterion of having no system inherent cross-polarization, which is one of the great advantages of the CCR. In practice, the cross polarization purity and field distribution of the range antenna as well as diffraction effects from the serrated reflector edges produce ripples in the uniform distribution of the overall testzone field. Therefore, the calculated plane wave spectrum is appropriately gated and back propagated to the main reflector in order to locate any echo sources as well as to visualise contributions from different parts of the CCR. The numerical results clearly show the effects of the serrated CCR, i.e. its contribution to cross-polarized field distributions of the overall test-zone field. In order to test the proposed method against experimental data, which are not in a suitable format for the FFT, the measured data are interpolated to an equally spaced grid in a Cartesian coordinate system. The experimental results, which are obtained by processing both co- and cross-polar measurements, show very good agreement compared to synthetic data.