Why should they have their own radar head?
Because for an airport in busy uncontrolled airspace, like DSA, it is quite* helpful to be able to see the unknown microlite that is crossing your final approach 3 miles out at 1000', quite legitimately not talking to you, when you have a 767 or suchlike plodding down your ILS. Or the Tornado closing on it from behind doing 400kt at low level, for that matter.
(*this is sarcasm)
in exactly the same way as Swanick work before you start!
Not quite. Swanwick rarely work traffic down to ground level, or in uncontrolled airspace. They tend to work within full radar cover.
Anyone know where the DSA secondary feed is from, out of interest? The Scampton head?