Improved version of the inverse Chebyshev filter

The inverse Chebyshev function is formed by a transformation of a rational equiripple function defined by two polynomial Chebyshev functions of the same order. Since the transformation moves the finite complex zeros of the original rational function to the imaginary axis, its main imperfections, such as low selectivity and relatively large Q factors of the zeros, are eliminated. Extremely low pole-Q factors of the initial function are retained, providing a low sensitivity and a good group delay.