Radar is a set of scientific methods and technical means used to determine the coordinates and characteristics of an object by means of radio waves. The object under investigation is often referred to as a radar target (or simply a target).
Principle of radar
Radio equipment and facilities designed to perform radar tasks are called radar systems or devices (radar or radar). The basics of radar are based on the following physical phenomena and properties:
- In the propagation medium, radio waves, meeting objects with different electrical properties, are scattered on them. The wave reflected from the target (or its own radiation) allows radar systems to detect and identify the target.
- At long distances, the propagation of radio waves is assumed to be rectilinear, with a constant speed in a known medium. This assumption makes it possible to measure the range to the target and its angular coordinates (with a certain error).
- Based on the Doppler effect, the frequency of the received reflected signal calculates the radial velocity of the radiation pointregarding RLU.
Historical background
The ability of radio waves to reflect was pointed out by the great physicist G. Hertz and the Russian electrical engineer A. S. Popov at the end of the 19th century. According to a patent dated 1904, the first radar was created by the German engineer K. Hulmeier. The device, which he called a telemobiloscope, was used on ships that plowed the Rhine. In connection with the development of aviation technology, the use of radar looked very promising as an element of air defense. Research in this area was conducted by leading experts from many countries of the world.
In 1932, Pavel Kondratievich Oshchepkov, a researcher at LEFI (Leningrad Electrophysical Institute), described the basic principle of radar in his works. He, in collaboration with colleagues B. K. Shembel and V. V. Tsimbalin in the summer of 1934 demonstrated a prototype radar installation that detected a target at an altitude of 150 m at a distance of 600 m.
Types of radar
The nature of the electromagnetic radiation of the target allows us to speak of several types of radar:
- Passive radar explores its own radiation (thermal, electromagnetic, etc.) that generates targets (rockets, aircraft, space objects).
- Active with an active response is carried out if the object is equipped with its own transmitter and interaction with itoccurs according to the "request - response" algorithm.
- Active with a passive response involves the study of the secondary (reflected) radio signal. The radar station in this case consists of a transmitter and a receiver.
- Semi-active radar is a special case of active, in the case when the receiver of reflected radiation is located outside the radar (for example, it is a structural element of a homing missile).
Each species has its own advantages and disadvantages.
Methods and equipment
All means of radar according to the method used are divided into radars of continuous and pulsed radiation.
The first contain a transmitter and a receiver of radiation, acting simultaneously and continuously. According to this principle, the first radar devices were created. An example of such a system is a radio altimeter (an aircraft device that determines the distance of an aircraft from the earth's surface) or a radar known to all motorists to determine the speed of a vehicle.
In the pulsed method, electromagnetic energy is emitted in short pulses of a few microseconds. After generating a signal, the station works only for reception. After capturing and registering the reflected radio waves, the radar transmits a new pulse and the cycles repeat.
Radar operating modes
There are two main modes of operation of radar stations and devices. The first is space scanning. It is carried out according to a strictsystem. With a sequential review, the movement of the radar beam can be circular, spiral, conical, sectoral in nature. For example, an antenna array can slowly rotate in a circle (in azimuth) while simultaneously scanning in elevation (tilting up and down). With parallel scanning, the review is carried out by a beam of radar beams. Each has its own receiver, several information flows are being processed at once.
Tracking mode implies a constant directivity of the antenna to the selected object. To turn it, according to the trajectory of a moving target, special automated tracking systems are used.
Algorithm for determining the range and direction
The speed of propagation of electromagnetic waves in the atmosphere is 300 thousand km/s. Therefore, knowing the time spent by the broadcast signal to cover the distance from the station to the target and back, it is easy to calculate the distance of the object. To do this, it is necessary to accurately fix the time of sending the impulse and the moment of receiving the reflected signal.
To obtain information about the location of the target, highly directional radar is used. The determination of the azimuth and elevation (elevation or elevation) of an object is made by an antenna with a narrow beam. Modern radars use phased antenna arrays (PAR) for this, capable of setting a narrower beam and characterized by a high rotation speed. As a rule, the process of space scanning is performed by at least two beams.
Main system parameters
FromThe tactical and technical characteristics of the equipment largely depend on the efficiency and quality of the tasks to be solved.
The tactical indicators of the radar include:
- View area limited by the minimum and maximum target detection range, allowable azimuth and elevation angles.
- Resolution in range, azimuth, elevation and speed (the ability to determine the parameters of nearby targets).
- Measurement accuracy, which is measured by the presence of gross, systematic or random errors.
- Noise immunity and reliability.
- The degree of automation of extracting and processing the incoming information data stream.
Specified tactical characteristics are laid down when designing devices through certain technical parameters, including:
- carrier frequency and modulation of generated oscillations;
- antenna patterns;
- power of transmitting and receiving devices;
- Overall dimensions and weight of the system.
On duty
Radar is a universal tool widely used in the military, science and national economy. The areas of use are steadily expanding due to the development and improvement of technical means and measurement technologies.
The use of radar in the military industry allows us to solve the important tasks of reviewing and controlling space, detecting air, ground and water mobile targets. Withoutradars, it is impossible to imagine equipment serving for information support of navigation systems and gunfire control systems.
Military radar is the core component of the strategic missile warning system and integrated missile defense.
Radio astronomy
Sent from the surface of the earth, radio waves are also reflected from objects in near and far space, as well as from near-Earth targets. Many space objects could not be fully investigated only with the use of optical instruments, and only the use of radar methods in astronomy made it possible to obtain rich information about their nature and structure. Passive radar for lunar exploration was first used by American and Hungarian astronomers in 1946. Around the same time, radio signals from outer space were also accidentally received.
In modern radio telescopes, the receiving antenna has the shape of a large concave spherical bowl (like the mirror of an optical reflector). The larger its diameter, the weaker the signal the antenna will be able to receive. Often, radio telescopes work in a complex manner, combining not only devices located close to each other, but also located on different continents. Among the most important tasks of modern radio astronomy is the study of pulsars and galaxies with active nuclei, the study of the interstellar medium.
Civil use
In agriculture and forestry radardevices are indispensable for obtaining information on the distribution and density of plant masses, studying the structure, parameters and types of soils, and timely detection of fires. In geography and geology, radar is used to perform topographic and geomorphological work, determine the structure and composition of rocks, and search for mineral deposits. In hydrology and oceanography, radar methods are used to monitor the state of the country's main waterways, snow and ice cover, and map the coastline.
Radar is an indispensable assistant for meteorologists. The radar can easily find out the state of the atmosphere at a distance of tens of kilometers, and by analyzing the data obtained, a forecast is made of changes in weather conditions in a particular area.
Prospects for development
For a modern radar station, the main evaluation criterion is the ratio of efficiency and quality. Efficiency is understood as the generalized performance characteristics of the equipment. Creating a perfect radar is a complex engineering and scientific and technical task, the implementation of which is possible only with the use of the latest achievements in electromechanics and electronics, informatics and computer technology, energy.
According to experts' forecasts, in the near future the main functional units of stations of various levels of complexity and purpose will be solid-state active phased arrays (phased antenna arrays), which convert analog signals into digital ones. DevelopmentThe computer complex will fully automate the control and basic functions of the radar, providing the end user with a comprehensive analysis of the information received.
