Design of highly selective two-dimensional recursive fan filters by relaxing symmetry constraints
Zhiping Lin, Len T. Bruton, N.R. Bartley · Electronics Letters · 1988
We show for the design of quadrantally symmetric 2-D fan filters that it is unnecessarily restrictive to prescribe exact quadrantal symmetry, which requires that the denominator of the Z-transform transfer function be product-separable. Superior approximately symmetric fan filter designs can be achieved using nonseparable denominators.