SUMMARY

The following is a brief summary of the important points of this chapter.

A radar INDICATOR presents the information (video) from the radar receiver in a usable manner. The display usually consists of one or more of the coordinates of range, bearing, and altitude.

The CATHODE-RAY TUBE (crt) is the best available device for displaying the two-dimensional relationship produced by radar coordinates. The most commonly used crt displays are the A-SCOPE, the RHI, and the PPI. The A-scope presents range information only. The rhi displays range and height information. The ppi is the most widely used radar display indicator and presents range and bearing.

The range of a radar contact is determined by special RANGING CIRCUITS. The following three basic types of ranging circuits are used.

RANGE-GATE GENERATORS produce a movable gate that measures range based on elapsed time and can be used on A-scope and ppi displays.

RANGE-MARKER GENERATORS produce fixed interval range marks that can be used to estimate the range to a detected target. Range marks appear as an intensified series of vertical dots on an rhi and as concentric circles on a ppi.

The RANGE-STEP GENERATOR produces a movable step that is displayed on an A-scope presentation.

RADAR ANTENNAS are usually directional antennas that radiate energy in a one directional lobe or beam. The two most important characteristics of directional antennas are directivity and power gain. Radar antennas often use parabolic reflectors in several different variations to focus the radiated energy into a desired beam pattern. Other types of antennas used with radar systems are the corner reflector, the broadside array, and horn radiators.