I think you may be missing a key point of the system described in the article- it is passive, and does not transmit any signal. Instead it relies on RF already

I think you may be missing a key point of the system described in the article- it is passive, and does not transmit any signal. Instead it relies on RF already in the environment - radio, tv stations and the like. This makes the system far harder to detect and target. I recall hearing about a similar Chinese(?) system a little while ago which used the scatter from mobile phone signals.