The window is described in frequency domain by the expression:
$$ W(k) = \frac{Cheb(n-1, \beta * cos(pi * k/n))}{Cheb(n-1, \beta)}$$
with
$$\beta = cosh(1/(n-1) * acosh(10^{at/20}))$$
and \(Cheb(m,x)\) denoting the \(m\)-th order Chebyshev polynomial calculated
at the point \(x\).
Note that the denominator in \(W(k)\) above is not computed, and after
the inverse Fourier transform the window is scaled by making its
maximum value unitary.