A theoretical description of the IsoFilter(TM) rejection curve

In a 2008 AMTA paper the concept of the IsoFilter™ rejection curve was described. The steps to generate this rejection curve consist simply of (1) translating the coordinate origin of the measured pattern to a new location (2) performing a spherical modal analysis of the pattern, and (3) taking the total power in the lowest order mode as a measure of the strength of the radiation source at that location. Stepwise repetition of this process then generates the IsoFilter™ rejection curve. The basis for the process of generation was an empirical recipe for which no theoretical basis was presented. In this paper we relate the rejection curve to conventional electromagnetic theory. We begin with the general free space Green´s function assuming a general distribution of current sources, and show how one may plausibly describe the IsoFilter™ rejection curve, and how it operates to reveal an arbitrary source distribution.