Interesting that Biggin Hill was a wireless testing station in WW1; it was also used many years later as an evaluation site for three different VOR beacons, in the 1970's.
These were of the type utilising the Doppler principle (DVOR), and three suppliers built their own designs for circular planform steel decks at the airport to enable comparisons to be made of relative performance and costs.
There is now just one of these beacons remaining, which I presume to be the successful design type for this location.