If you are using latest version of MATLAB you can limit the axis using rlim. If you are in older version, after plotting the figure, get the axes and set the limits you want.
t = 0 : .01 : 2 * pi;
P = polar(t, 2 * ones(size(t)));
set(P, 'Visible', 'off')
polar(t, sin(2 * t) .* cos(2 * t), '--r')
ax = gca;
In the above ax have XLim and YLim, set it to the limits you want.