I shall have to see what can be found on its operating principles.
The principles are pretty simple, although I'm sure there's a lot of hard magic involved in practice.
Take an array of sensors (microphones, antennas, whatever), and imagine them picking up a sinusoidal signal that originates directly in front of the array. The distance from the source to each sensor is the same (assuming the source is far enough away), so the signals are all in phase. Add them together and they reinforce.
If the source is not directly in front, then sensors closer to it will pick up the signal before ones that are further away. If you add the received signals together now, you'll get partial or complete cancellation. But if you know the direction that the source is in, you can compensate for the delay. Shift the phase of the signal received by each sensor by the appropriate amount, and the result is all in phase.
Since you don't know what direction the signal is coming from (and, in fact, you'll generally have multiple signals coming from multiple directions), you try them all at once. For each possible direction, apply the appropriate phase shifts, and you'll see what's coming from from that direction.
Repeat this for each frequency in the range that you care about, and you get an image.
This sort of thing is common in radio astronomy. It's also the idea (in reverse) behind that Russian radar system that was discussed here recently.