Maybe they used the original tower from a previous radar head instead of building a new one?
Farnborough's Watchman was mounted on a concrete tower (with a lift in it in which the chairman of the CAA got stuck once) which was originally built for the Plessey AR1 in the early '60s and this, being outside the airfield boundary on land owned by Qinetiq, was only demolished in 2003 when the Raytheon ASR10 in the middle of the airfield was brought into use.
The old concrete tower was built on Ball Hill, where Sam Cody lost his life.