analical curve of polar formula in CST

Hello ,the structure is a sinuos curve that i managed to do by input of x,y table .
The problem in that method that is i cant do a sweep of the structure parameters.

The only way that i see is by this option of the photo presented bellow ,where formula input,but it accepts only Cartesian formula, where as my formula is polar.
tau=1.35
r=1:0.01:1.35;
phi=0.87*sin((log(r)*pi)/(log(tau)));
if i will transform it into Cartesian form, then i cant separate Y from X.
how can i solve this problem?

Thanks