Radar (radio detection and ranging)
Thursday, 22 March, 2018
What is Radar?
Radar is an acronym for "radio detection and ranging." A radar system usually operates in the ultra-high-frequency (UHF) or microwave part of the radio-frequency (RF) spectrum, and is used to detect the position or movement of objects.High-power radar, using large dish antennas, has been used to measure distances to the moon, other planets, asteroids, and artificial satellites. From unmanned spaceprobes, radar has been used to map Venus, whose surface is obscured at visible wave lengths by a thick layer of clouds. Radar has been employed by NASA(the U.S. National Aeronautics and Space Administration) to make highly detailed topographical maps of the earth's surface as well.
HOW DOES IT WORK?
TARGET DETECTION
Radars create an electromagnetic (EM) pulse that is focused by an antenna, and then transmitted through the atmosphere (Figure A).Objects in the path of the transmitted EM pulse, called "targets" or "echoes," scatter most of the energy, but some will be reflected back toward the radar (Figure B). The receiving antenna (normally also the transmitting antenna) gathers back-scattered radiation and feeds it to a "receiver." An EM pulse encountering a target is scattered in all directions. The larger the target, the stronger the scattered signal (Figure C). Also, the more targets, the stronger the return signal, that is, the targets combine to produce a stronger signal (Figure D).The radar measures the returned signal, generally called the "reflectivity." Reflectivity magnitude is related to the number and size of the targets encountered.
Types of Radar :
Land-Based Air Defense Radars:These radars cover all fixed, mobile, and transportable 2-D and 3-D systems used in the air defense mission.Battlefield, Missile Control, and Ground Surveillance Radars. These radars also include battlefield surveillance, tracking, fire-control, and weapons-locating radar systems, whether fixed, mobile, transportable, or man-portable.
Naval and Coastal Surveillance, and Navigation Radar:These radars consist of shipborne surface search and air search radars (2-D and 3-D) as well as land-based coastal surveillance radars.
Naval Fire-Control Radars:These are shipborne radars that are part of a radar-based fire-control and weapons guidance systems.
Airborne Surveillance Radars:These radar systems are designed for early warning, land and maritime surveillance, whether for fixed-wing aircraft, helicopters, or remotely piloted vehicles (RPV's).
Airborne Fire-Control Radars:Includes those airborne radar systems for weapons fire-control (missiles or guns) and weapons aiming.
Spaceborne Radar Systems. Considerable effort has been applied to spaceborne radar (SBR) research for intelligence, surveillance, and reconnaissance missions over the last 30 years. The Department of Defense (DOD) seems to be expressing new interest in SBR.
Military Air Traffic Control (ATC), Instrumentation and Ranging Radars:These include both land-based and shipborne ATC radar systems used for assisting aircraft landing, and supporting test and evaluation activities on test ranges. See Appendix B for descriptions of shipborne ATC radars.
Simple Pulse Radar:This type is the most typical radar with a waveform consisting of repetitive short-duration pulses. Typical examples are long-range air and maritime surveillance radars, test range radars, and weather radars. There are two types of pulse radars that uses the Doppler frequency shift of the received signal to detect moving targets, such as aircraft, and to reject the large unwanted echoes from stationary clutter that do not have a Doppler shift. One is called moving-target indication (MTI) radar and the other is called pulse Doppler radar. Users of pulse radars include the Army, Navy, Air Force, FAA, USCG, NASA, Department of Commerce (DOC), Department of Energy (DOE), U.S. Department of Agriculture (USDA), Department of the Interior (DOI), National Science Foundation (NSF), and Department of Treasury.
Moving-Target Indication (MTI) Radar:By sensing Doppler frequencies, an MTI radar can differentiate echoes of a moving target from stationary objects and clutter, and reject the clutter. Its waveform is a train of pulses with a low PRR to avoid range ambiguities. What this means is that range measurement at the low PRR is good while speed measurement is less accurate than at a high PRR's. Almost all ground-based aircraft search and surveillance radar systems use some form of MTI. The Army, Navy, Air Force, FAA, USCG, NASA, and DOC are large users of MTI radars.
Uses of Radar:
Radar is used for a wide array of applications, but primarily to detect precipitation and other meteorological events.
When looking into automotive engineering, anti-collision systems can be found in almost every modern vehicle. This radar type is a combination of UWB-radars and common Doppler-radars.
They can be used to detect obstacles in a distance of around 30 meters and measure their speed.
In geophysics radars, so called GPR-Systems, are used to analyze the ground to create soil profiles.
Conclusion:
With new technologies such as the Ultra-Wideband-Technology (UWB), the development of new radar applications is not
limited anymore. These systems are more frequently used in everyday applications and offer many advantages. They protect the health of people, guaranty safety and help to prevent accidents. To develop these kinds of systems electromagnetic simulation is applied. By introducing simulation into the development process engineers can predict and analyze i.e. the ideal position and radiation characteristics of antenna components or bidirectional influences of different components.One of the leading provider of simulation tools, Altair Engineering offers, with its EM product suite FEKO, solutions that can be used to virtually design and optimize radar systems. The application of these simulation solutions helps to optimize development processes, reduce development time and the number of prototypes needed. Hence systems can be developed faster and less expensive and the risk of aberrations can be reduced. In the end the user will benefit from better and less expensive products for everyday use.
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