Realization of a class of two-dimensional zero-phase recursive digital filters with variable cutoff boundary

Digital realization of a class of two-dimensional, zero-phase filters with variable cutoff boundary is given. The derivation of the 2-D transfer function is based on the transformation of a 1-D analog reference filter using a two-variable reactance function. Digital realization of the resulting 2-D transfer function is derived by using the generalized delay unit concept and cascade connections of two-port networks represented by their scattering matrices.