On the mapping of extended sources with nonlinear correlation antennas

In this paper nonlinear correlation antennas are reexamined in terms of coherence theory. Particular emphasis is given to an antenna system consisting of the correlation of the outputs of two arbitrary antennas. It is shown that such a system operates in a linear fashion for an extended incoherent source. In fact, a fiat spatial frequency response for this system can be obtained when, in particular, one antenna is a continuous array with a uniformly illuminated aperture, while the other is a simple interferometer.