RADAR Classification and Use
Radar systems, like cars, come in a variety of sizes and have different performance specifications. Some radar systems are used for air-traffic control at airports and others are used for long-range surveillance and early-warning systems. A radar system is the heart of a missile guidance system. Small portable radar systems that can be maintained and operated by one person are available as well as systems that occupy several large rooms.
The large number of radar systems used by the military has forced the development of a joint- services classification system for accurate identification. The Federal Aviation Agency (FAA) also makes extensive use of radar classification systems for commercial aircraft in-flight and landing control, but does not use the military radar classification system.
Radar systems are usually classified according to specific function and installation vehicle. Some common examples of radar classification are listed below:
Radar systems chart.
The joint-service standardized radar classification system further divides these broad categories for more precise identification. The military provides a listing of equipment identification indicators. Use of the table to identify a particular radar system is illustrated in the figure below. Note that for simplicity, only a portion of the table has been used in the illustration.
Joint service classification system.
No single radar system has yet been designed that can perform all of the many radar functions required by the military. Some of the newer systems combine several functions that formerly required individual radar systems, but no single system can fulfill all the requirements of modern warfare. As a result, modern warships, aircraft, and shore stations usually have several radar systems, each performing a different function.
One radar classification, called SEARCH RADAR, is designed to continuously scan a volume of space to provide initial detection of all targets. Search radar is almost always used to detect and determine the position of new targets for later use by TRACK RADAR. Track radar provides continuous range, bearing, and elevation data on one or more targets. Most of the radar systems used by the military are in one of these two categories, though the individual radar systems vary in design and capability.
Some radar systems are designed for specific functions that do not precisely fit into either of the above categories. The radar speed gun is an example of radar designed specifically to measure the speed of a target. The military uses much more complex radar systems that are adapted to detect only fast- moving targets such as aircraft. Since aircraft usually move much faster than weather or surface targets, velocity-sensitive radar can eliminate unwanted clutter from the radar indicator. Radar systems that detect and process only moving targets are called MOVING-TARGET INDICATORS (mti) and are usually combined with conventional search radar.
Another form of radar widely used in military
and civilian aircraft is the RADAR ALTIMETER. Just as some surface-based
radars can determine the height of a target, airborne radar can
determine the distance from an aircraft to the ground. Many aircraft use
radar to determine height above the ground. Radar altimeters usually
use frequency-modulated signals of the type discussed earlier in the
The preceding paragraphs indicated that radar
systems are divided into types based on the designed use. This section
presents the general characteristics of several commonly used radar
systems. Typical characteristics are discussed rather than the specific
characteristics of any particular radar system.
Search radar, as previously mentioned, continuously scans a volume of space and provides initial detection of all targets within that space. Search radar systems are further divided into specific types, according to the type of object they are designed to detect. For example, surface-search, air-search, and height-finding radars are all types of search radar.
A surface-search radar system has two primary functions: (1) the detection and determination of accurate ranges and bearings of surface objects and low-flying aircraft and (2) the maintenance of a 360- degree search pattern for all objects within line-of-sight distance from the radar antenna.
The maximum range ability of surface-search radar is primarily limited by the radar horizon; therefore, higher frequencies are used to permit maximum reflection from small, reflecting areas, such as ship masthead structures and the periscopes of submarines. Narrow pulse widths are used to permit a high degree of range resolution at short ranges and to achieve greater range accuracy. High pulse-repetition rates are used to permit a maximum definition of detected objects. Medium peak power can be used to permit the detection of small objects at line-of-sight distances. Wide vertical-beam widths permit compensation for the pitch and roll of own ship and detection of low flying aircraft. Narrow horizontal- beam widths permit accurate bearing determination and good bearing resolution. For example, a common shipboard surface-search radar has the following design specifications.
Transmitter frequency 5,450-5,825 MHz
Pulse width .25 or 1.3 microseconds
Pulse-repetition rate between 625 and 650 pulses per second
Peak power between 190 and 285 kW
Vertical beam width between 12 and 16 degrees
Horizontal beam width 1.5 degrees
Surface-search radar is used to detect the presence of surface craft and low flying aircraft and to determine their presence. Shipboard surface-search radar provides this type of information as an input to the weapons system to assist in the engagement of hostile targets by fire-control radar. Shipboard surface- search radar is also used extensively as a navigational aid in coastal waters and in poor weather conditions. A typical surface-search radar antenna is shown in the figure below.
Surface search radar.