Noob antenna question: in a phased array is most transmit energy lost to destructive interference?
I thought that the beam was just the region where the waves didn't destructively interfere
I thought that the beam was just the region where the waves didn't destructively interfere
No. Phased-array antennae can be up to 90% efficient [1]. You aren't losing energy to destructive interference so much as channeling it to the constructive modes. (Totally physically inaccurate, but I think analogously correct.)
[1] https://www.mwrf.com/technologies/embedded/systems/article/2...
A low gain direction is not the same as no signal though. With enough power you can overpower the main lobe signal.