الرادار - الالكترونيات .. الفيزياء

Radar - Electronics .. Physics

Radar

Radar is a compound word made up of the first letters of the words Radio Detection and Range Control. Its development was aided by the necessity of detecting enemy aircraft during World War II. It is based on beams of short radio wave pulses directed towards a distant object. Since these beams are narrow in width, they travel greater distances in the Earth's atmosphere than light does due to the inability of fine dust particles to disperse them. Then some of these pulses are reflected and return to the point from which they were launched, and the radar antenna picks them up and converts them electronically from the broadcast state to the reception state directly after each pulse. It is worth noting that the direction of the target is determined by the direction of the beam reflected by the radar. As for its distance from it, it is determined by the delay period that lasts between the transmission of the pulse and its capture, noting that the echo of the pulse is captured before the transmission of the pulse that follows it directly.

If the signal echo is captured after a time of n (a few microseconds), the distance between the antenna and the target will be h n 2, where h represents the speed of light.

In some radar devices, the speed of the moving target is determined by the shift of the echo frequency resulting from the presence of the Doppler effect.

The radar signal is then displayed on the cathode ray fluorescent screen. This tube is of the detector type, where the distance is represented horizontally and the time is represented vertically, or of the "radio position indicator" type, in which the target is represented by a spot on a radial line whose direction is determined by the direction of the antenna itself.

There are three conditions that must be met in the radar device group: a high frequency (ranging between 200 MHz and 15 GHz) that allows good reflection of waves on small objects, a large capacity that increases the strength of the reflected wave, and a good ability to direct, which contributes to good targeting of targets.

Regular valves are not able to provide the radar with the required frequency and power, and special devices such as the magnetron must be used, which is a three-way valve placed between the poles of an electromagnet and produces a high-frequency vibration that occurs as a result of the interaction between the electric and magnetic fields in it. (Radar is used to determine the locations of incoming aircraft).