Basic Principle of Operation
The basic principle of operation of primary radar is simple to understand. However, the theory can be quite complex. An understanding of the theory is essential in order to be able to specify and operate primary radar systems correctly. The implementation and operation of primary radars systems involve a wide range of disciplines such as building works, heavy mechanical and electrical engineering, high power microwave engineering, and advanced high speed signal and data processing techniques. Some laws of nature have a greater importance here.
Radar measurement of range, or distance, is made possible because of the properties of radiated electromagnetic energia
- 1. Reflection of electromagnetic waves. The electromagnetic waves are reflected if they meet an electrically leading surface. If these reflected waves are received again at the place of their origin, then that means an obstacle is in the propagation direction.
2. Electromagnetic energy travels through air at a constant speed, at approximately the speed of light,
- 300,000 kilometers per second or
- 186,000 statute miles per second or
- 162,000 nautical miles per second.
This constant speed allows the determination of the distance between the reflecting objects (airplanes, ships or cars) and the radar site by measuring the running time of the transmitted pulses.
3. This energy normally travels through space in a straight line, and will vary only slightly because of atmospheric and weather conditions. By using of special radar antennas this energy can be focused into a desired direction. Thus the direction (in azimuth and elevation of the reflecting objects can be measured.
These principles can basically be implemented in a radar system, and allow the determination of the distance, the direction and the height of the reflecting object.
(The effects atmosphere and weather have on the transmitted energy will be discussed later; however, for this discussion on determining range and direction, these effects will be temporarily ignored.)
Radar Principle
The electronic principle on which radar operates is very similar to the principle of sound-wave reflection. If you shout in the direction of a sound-reflecting object (like a rocky canyon or cave), you will hear an echo. If you know the speed of sound in air, you can then estimate the distance and general direction of the object. The time required for an echo to return can be roughly converted to distance if the speed of sound is known.
Radar uses electromagnetic energy pulses in much the same way, as shown in Figure 1. The radio-frequency (rf) energy is transmitted to and reflected from the reflecting object. A small portion of the reflected energy returns to the radar set. This returned energy is called an ECHO, just as it is in sound terminology. Radar sets use the echo to determine the direction and distanceof the reflecting object.
The term RADAR is an acronym made up of the words:
RAdio (Aim)* Detecting And Ranging
It refers to electronic equipment that detects the presence of objects by using reflected electromagnetic energy. Under some conditions a radar system can measure the direction, height, distance, course and speed of these objects. The frequency of electromagnetic energy used for radar is unaffected by darkness and also penetrates fog and clouds. This permits radar systems to determine the position of airplanes, ships, or other obstacles that are invisible to the naked eye because of distance, darkness, or weather.
Modern radar can extract widely more information from a target's echo signal than its range. But the calculating of the range by measuring the delay time is one of its most important functions.
Cesar Augusto Suarez
CI 17394384
CRF
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