I had this question on the physics community, but I thought this would be appropriate to cross-post here.
I read that in VLBI, the signals of microwaves (on the millimeter scale) are recorded and then later combined. A famous example of this is the Event Horizon Telescope which imaged the black hole. Presumably, the telescopes recorded the phase of the microwaves.
This tells me that it is possible to record the specific phase of a microwave, but I haven't seen any technology that can do this. Most oscilloscopes, for example, don't have high enough frequency to resolve such short time scales required to measure microwave phases.
My two questions are simple. Answers to either one would be helpful.
Is there any piece of technology that can measure the phase of a microwave? What technology is used anyways for VLBI to record phases?
Edit: When I said "phase" I meant to say the actual "magnitude" of the wave at any point in time, but I see it is more complicated.