Limitations of multiple feeds in a polarimetric-radar compact range

It is found that two feeds, one for transmit and one for receive, can be used in a polarimetric-radar compact range provided they are located symmetrically with respect to the reflector focus. Such a configuration will conserve the coherence of the polarization matrix. However, the use of four separate feeds, two for each transmit polarization and two for each receive polarization, will destroy the coherence of the polarization matrix for scatterers off of the range axis. Significant phase errors will be introduced between the elements of the polarization matrix with the result that the measured matrix will be incorrect.<>