Radar was an object-detection system which uses electromagnetic waves – specifically radio waves – to determine the range, altitude, direction, or speed of both moving and fixed objects such as spacecraft and missiles.
The radar dish, or antenna, transmitted pulses of radio waves or microwaves which bounced off any object in their path. The object thus returned a tiny part of the wave's energy to a dish or antenna which was usually located at the same site as the transmitter.
Radar, and the related lidar system which used laser beams, were commonly used in starships of the Post Diaspora. (HH1)
The AR-7(b) was the standard search radar mounted on dreadnoughts and superdreadnoughts of the People's Navy in the early 20th Century PD. (HH5)