There is a electric field in the far zone of the rectangular aperture antenna as shown below.
Antenna lies along the xy plane. $$E_{\theta}=\dfrac{jke^{-jkr}}{4\pi r}\dfrac{sin(0.5\lambda k sin\theta sin\phi)}{ksin\theta sin\phi}$$ $$E_{\phi}=\dfrac{jke^{-jkr}}{4\pi r} cos\theta \dfrac{cosh(\lambda k sin\theta cos\phi)-1}{\lambda k^2 sin^2\theta }$$
How can I find the first side lobe level of this kind of complicated pattern?
