Approximation of complex-valued 2-D frequency response specifications by separable-denominator digital filters. - Hartmut Brandenstein; Rolf Unbehauen (ICASSP, 1997)

Least-squares approximation of FIR by IIR digital filters. - Hartmut Brandenstein; Rolf Unbehauen (IEEE Trans. Signal Process., 1998)

Weighted least-squares approximation of FIR by IIR digital filters. - Hartmut Brandenstein; Rolf Unbehauen (IEEE Trans. Signal Process., 2001)