Surface-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 I 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.

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.

RADAR GUN

To understand how radar detectors work, you first have to know what they're de­tecting. The-concept of measuring vehicle speed with radar is very simple. A basic speed gun is just a radio transmitter and receiver combined into one unit A radio transmitter is a device that oscillates an electrical current so the voltage goes up and down at a certain frequency. This electricity generates electromagnetic energy, and when the current is oscillated, the energy travels through the air as an electromagnetic wave. A transmitter also has an amplifier that increases the intensity of the electromagnetic energy and an antenna that broadcasts it into the air.

A radio receiver is just the reverse of the transmitter. It picks up electromagnetic waves with an antenna and converts them back into an electrical current At its heart, this is all radio is — the transmission of electromagnetic waves through space.

Radar is the use of radio waves to detect and monitor various objects. The simplest junction of radar is to tell you how far away an object is. To do this, the radar device emits a concentrated radio wave and listens for any echo. If there is an object in the path of the radio wave, it will reflect some of the electromagnetic energy, and the radio wave will bounce back to the radar device. Radio waves move through the air at a constant speed (the speed of light), so the radar device can calculate how far away the object is based on how long it takes the radio signal to return.

Radar can also be used to measure the speed of an object, due to a phenomenon called Doppler shift. Like sound waves, radio waves have a certain frequency, the num­ber of oscillations per unit of time. When the radar gun and the car are both standing still, the echo will have the same wave frequency as the original signal. Bach part of the signal is reflected when it reaches the car, mirroring the original signal exactly.

But when the car is moving, each part of the radio signal is reflected at a different point in space, which changes the wave pattern. When the car is moving away from the radar gun, the second segment of the signal has to travel a greater distance to reach the car than the first segment of the signal. As you can see in the diagram below, this has the effect of «stretching out» the wave, or lowering its frequency. If the car is moving toward the radar gun, the second segment of the wave travels a shorter distance than the first segment before being reflected. As a result, the peaks and valleys of the wave get squeezed together The frequency increases.

Based on how much the frequency changes, a radar gun can calculate how quickly a car is moving toward it or away from it. If the radar gun is used inside a moving police car, its own movement must also be factored in. For example, if the police car is going 50 miles per hour and the gun detects that the target is moving away at 20 miles per hour, the target must be driving at 70 miles per hour. If the radar gun determines that the target is not moving toward or away from the police car, than the target is driving at exactly 50 miles per hour.

Radar (speed) gun — радиолокационный измеритель скорости

Radar detector— радарный детектор, антирадар

Translate the following text:

Radar system or technique for detecting the position, movement, and nature of a remote object by means of radio waves reflected from its surface. Although most radar units use microwave frequencies, the principle of radar is not confined to any particular frequency range. There are some radar units that operate on frequencies well below 100 megahertz (megacycles) and others that operate in the infrared range and above. The term radar, an acronym for radio detection and ranging, is also used to denote the ap­paratus for implementing the technique.