Radar is a combination of scientific methods and technical tools used to determine the coordinates and characteristics of an object by means of radio waves. An object under investigation is often referred to as a radar target (or simply a target).
The principle of radar
Radio engineering equipment and tools 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 medium of propagation of radio waves, encountering objects with other 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 large distances, the propagation of radio waves is assumed to be straightforward, at a constant speed in a known medium. This assumption makes it possible to measure the distance to the target and its angular coordinates (with a certain error).
- Based on the Doppler effect, the radial velocity of the radiation point relative to the XRD is calculated from the frequency of the received reflected signal.
Historical reference
The ability of the radio waves to reflect was indicated by the great physicist G. Herz and the Russian electrical engineer A.S. Popov at the end of the XIX century. According to a patent from 1904, the first radar was created by a German engineer K. Hülmeier. The device, which he called a telemobiloscope, was used on ships plowing 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 in many countries of the world.
In 1932, the main principle of radar was described in his work by a researcher at LEFI (Leningrad Electrophysical Institute) Pavel Kondratievich Oshchepkov. Him in collaboration with colleagues B.K. Shembel and V.V. In the summer of 1934, Tsimbalin demonstrated a prototype of a radar installation, which detected a target at an altitude of 150 m at a distance of 600 m. Further work to improve radar facilities was to increase their range and increase the accuracy of determining the location of the target.
Types of radar
The nature of the electromagnetic radiation of the target allows us to talk about several types of radar:
- Passive radar explores its own radiation (thermal, electromagnetic, etc.), which generates targets (rockets, planes, space objects).
- An active with an active response is carried out if the object is equipped with its own transmitter and interaction with it occurs 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 reflected radiation receiver is located outside the radar (for example, is a constructive 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 continuous and pulsed radar.
The former contain a transmitter and a radiation receiver, 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 surface of the earth) or a radar known to all motorists to determine the speed of a vehicle.
In the pulsed method, electromagnetic energy is emitted by short pulses for several microseconds. After generating a signal, the station only works on reception. After collecting and recording the reflected radio waves, the radar transmits a new pulse and the cycles are repeated.
Radar operating modes
There are two main modes of functioning of radar stations and devices. The first is space scanning. It is carried out according to a strictly specified system. With a sequential review, the movement of the radar beam can be circular, spiral, conical, sectorial in nature. For example, the antenna grill can slowly rotate in a circle (in azimuth), while simultaneously scanning in elevation (tilting up and down). In parallel scanning, the survey is carried out by a beam of radar rays. Each one has its own receiver; several information flows are being processed at once.
The tracking mode implies the constant direction of the antenna to the selected object. For its rotation, in accordance with the trajectory of a moving target, special automated tracking systems are used.
Range and Direction Algorithm
The propagation velocity of electromagnetic waves in the atmosphere is 300 thousand km / s. Therefore, knowing the time taken by the broadcast signal to cover the distance from the station to the target and vice versa, it is easy to calculate the remoteness of the object. For this, it is necessary to precisely record the time of sending the pulse and the moment of receiving the reflected signal.
To obtain information about the location of the target, directional radar is used. The azimuth and elevation (elevation or elevation) of an object is determined by an antenna with a narrow beam. Modern radars use phased antenna arrays (PAR) for this, which can set a narrower beam and have a high rotation speed. As a rule, the process of scanning space is accomplished by at least two rays.
Key system parameters
The efficiency and quality of the tasks to be solved largely depend on the tactical and technical characteristics of the equipment.
Tactical radar indicators include:
- The viewing area limited by the minimum and maximum target detection range, the permissible azimuth angle and elevation angle.
- 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.
- Immunity and reliability.
- The degree of automation of the extraction and processing of the incoming stream of information data.
The specified tactical characteristics are laid during the design of 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.
At the combat post
Radar is a universal tool that has become widespread in the military sphere, science and the national economy. 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 important tasks of the survey and control of space, the detection of air, ground and water mobile targets. Without radars, it is impossible to imagine equipment used to provide information support for navigation systems and gun fire control systems.
Military radar is a basic component of a strategic missile warning system and integrated missile defense.
Radio astronomy
Radio waves sent from the surface of the earth are also reflected from objects in near and far space, as well as from near-Earth targets. Many space objects could not be fully explored using optical instruments only, and only the use of radar methods in astronomy made it possible to obtain rich information about their nature and structure. For the first time, passive radar to study the moon was used by American and Hungarian astronomers in 1946. Around the same time, radio signals from outer space were accidentally received.
For modern radio telescopes, the receiving antenna has the shape of a large concave spherical bowl (like a mirror of an optical reflector). The larger its diameter, the weaker the signal the antenna can receive. Often, radio telescopes work in a complex way, 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 application
In agriculture and forestry, radar devices are indispensable for obtaining information about the distribution and density of plant masses, studying the structure, parameters and types of soils, timely detection of foci of ignition. 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 by radar methods, the state of the main waterways of the country, snow and ice cover, and mapping of the coastline are monitored.
Radar is an indispensable assistant to meteorologists. The radar can easily find out the state of the atmosphere at a distance of tens of kilometers, and an analysis of the data obtained makes a forecast of changes in weather conditions in a particular area.
Development prospects
For a modern radar station, the main evaluation criterion is the ratio of efficiency and quality. Efficiency is understood as generalized tactical and technical characteristics of equipment. Creating a perfect radar is a complex engineering and scientific-technical task, the implementation of which is possible only using the latest achievements in electromechanics and electronics, computer science and computer engineering, and energy.
According to experts, 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 array) that convert analog signals to digital. The development of the 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.