The shadow boundary integral for the reduction of truncation error in near-field to far-field transformations

An efficient strategy is proposed for the reduction of truncation error effects in near-field to far-field transforms. First, the near-field data are back propagated to the antenna aperture plane by means of standard near-field to near-field transformation techniques; then, only the samples falling inside the antenna aperture are retained, while the field distribution in the external frame of the antenna plane is efficiently reconstructed in terms of a diffraction integral along the aperture rim. To this end, the shadow boundary integral technique is used. Thus, a continuous field distribution is obtained in a large area on the antenna plane, and then propagated to the measurement plane to estimate additional near-field samples. As a result, the scan area is virtually enlarged without requiring additional measures. The effectiveness of the proposed techniques for general scanning conditions is demonstrated by numerical results relevant to theoretical as well as measured near field data.