Complex Chebyshev approximation for IIR digital filters using an iterative WLS technique

A technique for designing IIR (infinite impulse response) filters with a complex-valued frequency response is proposed. The complex logarithmic error, whose real and imaginary parts represent the log magnitude and phase errors, respectively, is minimized in the Chebyshev sense using an iterative weighted-least-squares (WLS) technique in the frequency domain. Both the log magnitude and phase errors of the resulting filter become nearly equiripple. Filter coefficients at each iteration are efficiently computed using a fast recursive algorithm for a set of linear equations which is derived from the WLS problem