Plan-Position indicator (PPI):

• This is an intensity- modulation type displays system which indicates both range and azimuth angle of the target simultaneously in polar co-ordinate as shown in figure.
• The Demodulated echo signals from the receivers is applied to the grid of the CRT which is biased slightly beyond cutoff.
• Only when Blips corresponding to the targets occur, a saw tooth current applied to a pair of coils(on opposite side of the neck of the tube) flows.
• Thus, a beam is made to deflect radially outward from the center and also continuously around the tube(mechanically) at the same angular velocity as that of the antenna.
• The brightness spot at any point on the screen indicates the presence of an object there.
• Normally PPI screens are circular with a diameter of 30cm or 40cm. Long persistence phosphors are used to ensure that the PPI screen dose not flicker.