RADAR DETECTING METHODS

Given the range information, the operator knows the distance to an object, but information on bearing is still required to determine in which direction from the ship the target lies. Bearing Radar bearing is determined by the echo signal strength as the radiated energy lobe moves past the target. Since search radar antennas move contin- uously, the point of maximum echo return is deter- mined either by the detection circuitry as the beam passes the target or visually by the operator. Weapons control and guidance radar systems are positioned to the point of maximum signal return and are main- tained at that position either manually or by automatic tracking circuits. TRUE BEARING.— The angle between true north and a line pointed directly at a target is called the true bearing (referenced to true north) of a radar target. This angle is measured in the horizontal plane and in a clockwise direction from true north. RELATIVE BEARING.— The angle between the centerline of your ship or aircraft and a line pointed directly at a target is called the relative bear- ing of the radar target. This angle is measured in a clockwise direction from the centerline. Most surface- search radars provide only range and bearing infor- mation. If the operator were to have a need to direct air traffic or to track incoming missiles, the radar would also have to provide altitude. Both true and relative bearing angles are illustrated in figure 1-2. Altitude An operator can determine the altitude of a target by adjusting a movable height line on a height indica- tor to the point where the line bisects the center of the target. The altitude is then displayed by an altitude dial or a digital readout. A search radar system that Figure 1-2.—True and relative bearings. detects altitude as well as range and bearing is a three- dimensional (3-D) radar. Altitude or height-finding radars use a very nar- row beam in the vertical plane. This beam is scanned in elevation, either mechanically or electronically, to pinpoint targets. Tracking and weapons-control radar systems commonly use mechanical elevation scanning techniques that require mechanically moving the an- tenna or the radiation source. Most air-search radars use electronic elevation scanning techniques. Some older air-search radar sys- tems use a mechanical elevation scanning device; however, these are being replaced by electronically scanning radar systems. RADAR DETECTING METHODS Radar systems are normally divided into opera- tional categories based on energy transmission meth- ods. Although the pulse method is the most common method of transmitting radar energy, two other meth- ods are sometimes used in special applications. These are the continuous-wave method and the frequency- modulation method. 1-4