Bistatic RCS calculations from cylindrical near-field measurements - Part I: Theory

A theory is presented for computing scattered far fields of targets from cylindrical near-field measurements. The targets are illuminated by plane waves and measured in a radio anechoic chamber on a cylindrical scan surface. The scattered field on the scan cylinder is obtained by background subtraction. The near-field data is truncated at the top, bottom, and angular edges of the scan cylinder. These truncation edges can cause inaccuracies in the computed far fields. Correction techniques are developed for the top and bottom truncation edges. The cylindrical wave expansions automatically apply angular tapers to the near-field data that reduce the effect of the angular truncation edges. The taper functions depend on the angular sample spacing and are related to the currents induced on perfectly electrically conducting PEC cylinders in related scattering problems. The method of stationary phase is employed with asymptotic expressions for the taper functions to determine the area on the scan cylinder that is most important for computing the far field in a given direction. The theory is validated through numerical examples involving electrically large scatterers. The edge-correction techniques significantly increase the accuracy of the computed far field. A companion paper presents experimental results.