Design of a Equiangular Spiral Antenna

Hi everyone,

I want to design an Equiangular Spiral Antenna, but I need some helps with designing the antenna, how could I define the inner radius and the outer radius, number of turns and..............
thanks,

Added after 20 minutes:

I forgot say that, this antenna should work in the Ku band (12Ghz-18Ghz)
thanks,

Added after 1 hours 29 minutes:

If we use the relationship mentioned in Balanis Antenna Theory and Design book, we should use 2*pi*r = c/f (for both inner radius and outer radius), but this seems irrational, because then the outer radius will be equal to 3.821 mm ! and this radius is very small to build this antenna, I know that I am somewhere wrong.could anyone help me?