The Ground Based Radar, or GBR, refers to the proposed X-Band tracking and discrimination radar for the Ground-Based Midcourse Defense system (GMD, formerly called National Missile Defense or NMD).

The GBR family of radars has been designed by Raytheon. They are intended to be the primary fire-control and kill-assessment radars in the interception of incoming ballistic missiles. In the GMD system, GBRs are to be placed at strategic locations around the world to provide adequate coverage.

There exists a current X-Band or GBR prototype that has been used in testing of the GMD system. This prototype is currently installed at the Reagan Test Site on the Kwajalein Atoll in the Pacific Ocean. This protoype consists of a very large phased-array antenna system, with over 80,000 individual transmit and recieve modules. The antenna face is mounted on hardware for rotations in both the elevation and azimuthal axes, allowing for tracking in all directions.

This radar is impressive, but at no small cost. I have heard figures of around $2 billion for the prototype. Your tax dollars at work.