It is important to note that the antennae in a phased array (TRMs) cannot be "steered" individually: it is the electronics that creates a beam by timing the transmit and receive signals to a number of antennae. It's similar to the way an array of atoms creates a pattern of beams in x-ray crystallography, if that makes it clearer.
This does also mean that the whole array can be pointed in multiple directions at once: The only limitation is the number of phase shifters coming off of each antenna (if the signals are directly sampled and then the beam forming is done in software you are then only limited by your processing power. I'm not sure if this is currently possible in radar but I've seen it done for sonar).
Yes, you're right, I shouldn't have simplified it that much. Upvoted you because your comment deserves more attention.
The steering uses amplitude and phase shifting to create beams through constructive or destructive interference. All very fascinating stuff, and it allows for additional uses like jamming and directional communications links.
