Question

List different display methods used in Radar. Explain any one display method.

Answer 1

Display methods used in RADAR are given below.

1. A-Scope

2. PPI

3. Automatic target detection

A scope:

 

This is the most popular type of the deflection modulation type display system which indicates the range of the target. The A-scope display, shown in figure, presents only the range to the target and the relative strength of the echo. Such a display is normally used in weapons control radar systems. The bearing and elevation angles are presented as dial or digital readouts that correspond to the actual physical position of the antenna. The A-scope normally uses an electrostatic-deflection crt. The sweep is produced by applying a sawtooth voltage to the horizontal deflection plates. The electrical length (time duration) of the sawtooth voltage determines the total amount of range displayed on the crt face. The ranges of individual targets on an A-scope are usually determined by using a movable range gate or step that is superimposed on the sweep. In addition to this there are various signals displayed on the screen corresponding to:

o Ground clutter i.e. echoes from various fixed objects near the transmitter & from the ground.

o Grass noise i.e. an almost constant amplitude & continuous receiver noise.

o Actual targets. These signals are usually large.

OR

PPI Display:

 

This is an intensity modulation type display system which indicates both range & azimuth angle of the target simultaneously in polar coordinates. The demodulated echo signals from the receiver are applied to the grid of the CRT which is biased slightly beyond cut-off. The ppi scope shown in figure is by far the most used radar display. It is a polar coordinate display of the area surrounding the radar platform. Own ship is represented as the origin of the sweep, which is normally located in the center of the scope, but may be offset from the center on some sets. The PPI uses a radial sweep pivoting about the center of the presentation. This results in a map-like picture of the area covered by the radar beam. A longpersistence screen is used so that the display remains visible until the sweep passes again. Bearing to the target is indicated by the target's angular position in relation to an imaginary line extending vertically from the sweep origin to the top of the scope. The top of the scope is either true north(when the indicator is operated in the true bearing mode) or ship's heading (when the indicator is operated in the relative bearing mode)