Plotting 2-D Ambiguity Function

How can I plot, analytically not using the closed formula, the Radar Ambiguity function in Matlab:

Assume that S(t)= rect(t/2)

I need to plot it for -2<tau<2 and -2.5<f<2.5

\chi (\tau ,f)=\int_{\infty }^{\infty}s(t)s^{*}(t-\tau)e^{j2\pi ft}dt

The equation is in the attached file.

I need to plot X(tau,f)^2