How to find attenuation constant
How about this.
$$a+jb=\ln(x+jy)$$
$$e^{a+jb} = x+jy$$
$$e^a\angle b = x+jy$$

Now it is just a matter of converting the coordinates.

$$a=\ln{(x^2+y^2)}$$
$$b=\tan^{-1}\left(\frac{y}{x}\right)$$