You can change to polar coordinates in sketcher.
Start your sketch.
Select Utilities > Sketcher Preferences
Select the parameters tab.
In the Grid box, change from cartesian to polar.
Now you can sketch in polar coodinates.
You can also create a datum curve from equation.
Select Insert > Datum > Curve > From Equation > Done.
Choose Csys Type to change between Cartesian (x, y, z), Cylindrical (r, theta, z), and Spherical coordinate systems (r, theta, phi).
Select Csys to specify the origin of your sketch.
Select Equation and enter your equation.
Good luck.