Plan position indicator
Overview
 
The plan position indicator (PPI), is the most common type of radar display
Radar display
Modern radar systems typically use some sort of raster scan display to produce a map-like image. In the past, notably during the early days of radar development, such displays were difficult to produce for a number of reasons. Several different display types were developed during this...

. The radar antenna is usually represented in the center of the display, so the distance from it and height above ground can be drawn as concentric
Concentric
Concentric objects share the same center, axis or origin with one inside the other. Circles, tubes, cylindrical shafts, disks, and spheres may be concentric to one another...

 circles. As the radar antenna rotates, a radial trace on the PPI sweeps in unison with it about the center point.
The radar antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...

 sends pulses while rotating 360 degrees around the radar site at a fixed elevation angle.
 
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