A Theoretical Description of the IsoFilter Rejection Curve
Author: Doren W. Hess
Publication: EuCAP 2011
Copyright Owner: IEEE
The early work with the IsoFilterTM technique demonstrated that the radiation emanating from the aperture of a horn, located several wavelengths above a ground plane, could be separated from the radiation due to the sidelobe and backlobe illumination of the ground plane itself. The success of this demonstration encouraged us to pursue further the question of how well the IsoFilterTM technique worked to suppress other types of secondary signals such as signals coming from other elements of an array antenna or another individual first-order primary radiator nearby.  In the process of evaluating the goodness of the secondary signal suppression we devised a method for identifying the locations and strengths of an antenna's radiation sources that is an alternative to conventional back-projection. The alternative method utilizes the antenna's far-field measured radiation pattern and successive spherical modal analyses to ascertain the relative strength of the antenna's sources that give rise to its far field. We believe that this alternative technique has applicability to the general problem of antenna diagnostics. Please see the Figure below for an example of an IsoFilterTM rejection curve. 
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