Phasing the difference

The SuperDARN radar network is used in upper atmospheric research and one of the radars is in Longyearbyen, Svalbard. In the main array, there are 16 individual twin-terminated folded dipole antennas that are used at selected frequencies in the 8-20MHz range (HF).

Part of the main antenna array of the Svalbard SuperDARN radar

Radio science based on data from a faulty radar is not particularly desirable. So, one of the regular operational health checks is to verify that the phasing matrix in the Svalbard radar works correctly. This is done by feeding a known signal into the radar and measuring the phase difference to the signal that has gone through the system. In the end, the measured phase differences are compared with the theoretical (design) values. Any large differences and the beamforming in the phased antenna array will not work as expected.

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

In the end, this year's measurements look good and, as of now, I don't think we need to open the electronics racks to see what might be wrong. Whew!

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.