Limitations of multiple feeds in a polarimetric-radar compact range

摘要

The compact range has become widely used as a means of simulating far-field free-space conditions for RCS measurements. The most obvious way to illuminate such a range is to place a single feed at the focus of the lens or reflector system which collimates the field. However, in order to achieve greater isolation between the radar transmitter and receiver over wide bandwidths, two feeds are often used. Recently, interest has increased in the use of the compact range for performing complete polarimetric measurements, and the idea of similarly achieving greater polarization isolation through the use of multiple feeds is enticing. However, when the system is intended to measure the coherent polarization scattering matrix, the use of multiple feeds can lead to serious errors if the feed system is not carefully considered. It is well known that the use of a separate transmit and receive feed will result in a small bi-static angle for the RCS measurement. Often, this is considered acceptable and of no consequence to the validity of the data. As will be shown, the use of separate transmit and receive feeds can cause phase errors between the elements of the polarization scattering matrix. The situation is made worse by the fact that the magnitude of these errors depends on the location of the scatterer with respect to the range axis. This position dependence makes post-measurement correction of the data difficult if not impractical. 3 refs.