# Determining the correct sidelobe envelope

I need to determine the correct sidelobe envelope for various VSAT antennas. Given the radiation pattern (this one, for example http://www.gdsatcom.com/vsat/technical_docs/patterns/6000-023.pdf), how can I determine whether it is 29-25 log theta or 32-25 log theta?

It is my understanding that it depends on the off-axis angle (theta), but I don't know how it can be calculated. I think I've also seen somewhere that it depends on the azimuth and elevation, but I don't see how exactly they influence the off-axis angle.

For example, you would use the formula $29 - 25 \log \theta$ whenever $\theta$ is between 26.3 and 48 degrees.