RADAR stands for radio detection and ranging. Radio waves range from 300 GHz to 30 Hz. Modern radar uses higher frequency of waves for detection. These waves are microwaves (300 MHz-300 GHz). Microwaves are types of radio waves and are used in the radar detection.
The electromagnetic wave which has highest frequency is gamma wave but it is not used for radar detection.
Hence, the correct answer is microwaves are the type pf radio waves which have the highest frequency and are used in radar detection.
