الكشف وتحديد المدى بواسطة الراديو ( الرادار ) .. الإلكترونيات

Detection and Ranging by Radio (Radar)
.. Electronics

Detection and Ranging by Radio. (Radar)

If an aircraft or other spacecraft happens to pass in the path of a radio signal, a portion of the energy of the rays is reflected in the form of an (echo) that returns again to the device that sent it. Figure (238) shows a transmitting station A emitting pulses N with a time of one microsecond, and at a very high frequency, with a time period of 2500 microseconds between each pulse. These pulses are followed by periods of rest interspersed with other pulses, which are the echoes that the receiver picked up. Since the speed of the waves is known, the distance to the target can be determined by measuring the time it took for the signal to go and return. This period can also be seen directly on a cathode beam moving from left to right on the LED screen (238). In addition, the scale can be numbered in the same units of distance.

It is known that the radar equipment known as surface location radar can determine the distance to which the object is. In addition, the rotation of the directed antenna, and the deflection process that takes place from the center of the tracking tube and rotates with the antenna, are sufficient to determine the direction of the target and its distance from the transmitting station. Since the scanning tube and the antenna rotate at the same time, the echoes emitted by the objects surrounding the radar form a flat image on its screen. The cathode ray can be brighter at specific points that form, as a result of their rotation, rings that are used to facilitate the process of determining the range (240). The distance between these rings can also be expanded or reduced at the same time according to the speed of rotation of the trace so that we can detect larger areas as needed.

238 - Echo on the cathode ray valve.

239 - Rotating antenna with an angular direction trace.

Some precision radars used to assist aircraft landing are equipped with two antennas, one of which scans with a narrow beam, and the other scans vertically (241). Horizontal and vertical scanning can also be combined to create a three-dimensional scan to determine the aircraft's location in the air, as one group prepares a two-dimensional map of the aircraft while the second group gives the value of the height above the ground, or the third dimension.

240 - Range and angle markings on surface location radar.

241 - Radar with precise target approach range determination.

242 - Low-approach target range determination system.

The low-approach device used to assist aircraft landing includes a vertical signal to determine the runway, and a horizontal signal to determine the landing path. As for radar guidance devices, they are arranged in the outer, middle and near positions (242) and radiate vertically.

As for sounding devices (sonar), they are used to determine the distance separating an object in the water from the seabed. In this device, high-frequency signals are amplified before passing through an electronic opening circuit that directs them towards an energy converter (243). Then the echo of the signal reflected from the depths is captured by a receiver. By knowing the time and speed of the transmitted signal, the electronic beam in the receiver can determine the distance from the seabed.