Design of three-dimensional spherically symmetric IIR digital filters with real and complex coefficients using spectral transformations

Presents the design method of 3-D spherically symmetric IIR digital filters (with real coefficients) by means of 1-D digital to 3-D digital spectral transformations which is in the separable form. This is the generalization of Harn and Shenoi´s method. Proposed method can be applied to cutoff radius ω_c up to 0.8 π. Since the spectral transformation function used is separable, realization and stability check of the transformation are easy and the number of parameters to be determined is very few. However, filters with ω _c>0.8 π cannot be designed by this method because the undesirable passband regions cannot be eliminated perfectly. Therefore, also presented is the design method of 3-D spherically symmetric IIR complex coefficient digital filters by transformation in which there is no restriction at all for ω_c