ADS-B transponders are now available for even the smallest UAV/Drones and will be mandatory in controlled airspace in the USA in 2020. Any UAV appearing on primary radar, or any other detection system, and not so equipped will be immediately identified as a potential threat and targeted appropriately. Perhaps the UK should pass similar legislation and simply make it an offence to own or operate a drone without ADS B? The cost to the operator is low and it would make prosecution for illegal use much more clear cut.
Why is the FAA transitioning away from radar and towards ADS-B technology?
ADS-B is an environmentally friendly technology that enhances safety and efficiency, and directly benefits pilots, controllers, airports, airlines, and the public. It forms the foundation for NextGen by moving from ground radar and navigational aids to precise tracking using satellite signals.
With ADS-B, pilots for the first time see what controllers see: displays showing other aircraft in the sky. Cockpit displays also pinpoint hazardous weather and terrain, and give pilots important flight information, such as temporary flight restrictions.
ADS-B reduces the risk of runway incursions with cockpit and controller displays that show the location of aircraft and equipped ground vehicles on airport surfaces – even at night or during heavy rainfall. ADS-B applications being developed now will give pilots indications or alerts of potential collisions.
ADS-B also provides greater coverage since ground stations are so much easier to place than radar. Remote areas without radar coverage, like the Gulf of Mexico and parts of Alaska, now have surveillance with ADS-B.
Relying on satellites instead of ground navigational aids also means aircraft will be able to fly more directly from Point A to B, saving time and money, and reducing fuel burn and emissions.
The improved accuracy, integrity and reliability of satellite signals over radar means controllers eventually will be able to safely reduce the minimum separation distance between aircraft and increase capacity in the nation's skies.
For those interested;
https://uavionix.com/products/ping2020/