Highly selective three-dimensional recursive beam filters using intersecting resonant planes

It is shown that three-dimensional (3-D) recursive filters, having passbands contained within uniform-width slices in
\omega_{1} - \omega_{2} - \omega_{3}
space may be used to realize highly selective low-order 3-D recursive beam filters. These filters are capable of selectively transmitting spatially planar 3-D signals in quadrants where at least one of the frequency components is negative in
\omega_{1} - \omega_{2} - \omega_{3}
space.