Phasing the difference
|Part of the main antenna array of the Svalbard SuperDARN radar
|Good ol' analog electronics with lots of cables and blinking lights
For each individual antenna there are 16 beam "positions", or pointing directions, to measure. Connect the cables, configure beam, measure, write down the figures into the measurement logbook, disconnect cables and repeat until boredom. There are actually 20 antennas with 16 in the main array and 4 in the interferometer array, so that makes 320 very repetitive measurements. Ah, yes, that's for channel A, but there is also channel B...
|A half-empty table for channel A makes you wonder about the meaning of life
As a sidenote, a more modern approach – especially when the number of antennas is large – is to use digital beamforming. This is the implementation, for example, in EISCAT 3D. There will undoubtedly be a blog post about that in future.