How can I find direction of the main beam of an antenna if antenna has radiation intensity as following?
$$U=[\dfrac{sin(5\pi cos\theta)}{10sin(\pi cos(\theta/2))}]^2$$ Where $$0<\theta<\pi$$
My first trial is to find the places where derivatives equal to zero. But the results also give places of the nulls. So, how should I distinguish themain beam between the all nulls (zeros) and sidelobe peaks (local maximas)?