For a quick moderately accurate overview, see http://en.wikipedia.org/wiki/Miniature_UAV

A miniature UAV or Small UAV (SUAV), is an unmanned aerial vehicle small enough to be man-portable.

Miniature UAVs range from micro air vehicles (MAVs) that can be carried by an infantryman, to man-portable UAVs that can be carried and launched like an infantry anti-aircraft missile.

Here are a couple of documents about using radar aboard MAVs:
http://www.ssrrc.dtc.umn.edu/docs/RadarBasedDetection.pdf Radar-Based Detection and Identification for Miniature Air Vehicles

http://hal.inria.fr/docs/00/19/59/33/PDF/fsr_53.pdf Reactive Collision Avoidance for Unmanned Aerial Vehicles using Doppler Radar