Radar Technology Training Tutorial
The radar technology tutorial is intended to give you the big picture and general overview about radar. This tutorial is useful for learning general concepts, definition, applications, and history of radar. This tutorial acts as a learning map, demonstrating what you need to learn about radar technology.
Radar Description and History
RADAR stands for Radio Detection and Ranging System. It generally consists of a transmitter which produces an electromagnetic signal which is radiated into space by an antenna. When this signal strikes any object, it gets reflected or reradiated in many directions. This reflected or echo signal is received by the radar antenna which delivers it to the receiver, where it is processed to determine the geographical statistics of the object.
The range is determined by the calculating the time taken by the signal to travel from the RADAR to the target and back. The target’s location is measured in angle, from the direction of maximum amplitude echo signal, the antenna points to. To measure range and location of moving objects, Doppler Effect is used.
The origins of radar began in the late 19th century with experiments by Heinrich Hertz who proved that radio waves were reflected by metallic objects. This was also suggested in studies on electromagnetism by James Clerk Maxwell. But it wasn’t until the early 20th century that systems able to use this principle started to show up. German inventor Christian Hülsmeyer first used the basics of radar to build a simple ship detection device to help avoid collisions in fog.
The primary parts of a basic radar system are usually described as:
- A Transmitter: It can be a power amplifier like a Klystron, Travelling Wave Tube or a power Oscillator like a Magnetron. The signal is first generated using a waveform generator and then amplified in the power amplifier.
- Waveguides: The waveguides are transmission lines for transmission of the RADAR signals.
- Antenna: The antenna used can be a parabolic reflector, planar arrays or electronically steered phased arrays.
- Duplexer: A duplexer allows the antenna to be used as a transmitter or a receiver. It can be a gaseous device that would produce a short circuit at the input to the receiver when transmitter is working.
- Receiver: It can be super heterodyne receiver or any other receiver which consists of a processor to process the signal and detect it.
- Threshold Decision: The output of the receiver is compared with a threshold to detect the presence of any object. If the output is below any threshold, the presence of noise is assumed.
Application Areas of Modern Radar
- In air defense it is used for target detection, target recognition and weapon control (directing the weapon to the tracked targets).
- In missile system to guide the weapon.
- Identifying enemy locations in map.
- To guide the space vehicle for safe landing on moon
- To observe the planetary systems
- To detect and track satellites
- To monitor the meteor
Air Traffic Control
- To control air traffic near airports. The Air Surveillance RADAR is used to detect and display the aircraft’s position in the airport terminals.
- To guide the aircraft to land in bad weather using Precision Approach RADAR.
- To scan the airport surface for aircraft and ground vehicle positions.
RADAR can be used for observing weather or observing planetary positions and monitoring sea ice to ensure smooth route for ships.
Ground Traffic Control
RADAR can also be used by traffic police to determine speed of the vehicle, controlling the movement of vehicles by giving warnings about presence of other vehicles or any other obstacles behind them.
Common Types of Radar
Radar systems, used today by many different sectors, are classified under various categories according to function and purpose.
1. Bistatic radar
Bistatic radar is a radar system that comprises of a transmitter and a receiver that are separated by a distance that is equal to the distance of the expected target. A radar in which the transmitter and the receiver are located at the same place is known as a monastic radar. Most long range surface-to-air and air-to-air missiles employ the use of bistatic radar.
2. Continuous wave radar
A continuous wave radar is a type of radar where a known stable frequency continuous wave radio energy is transmitted and then received from any of the objects that reflect the waves. A continuous wave radar uses Doppler technology which means the radar will be immune to any form of interference by large objects that are stationary or slow moving.
3. Doppler radar
A Doppler radar is a special form of radar that employs the use of Doppler Effect to produce velocity data about an object at a given distance. This is achieved by sending electromagnetic signals towards a target and then analyzing how the object motion has affected the frequency of the returned signal. This variation has the capacity to give extremely accurate measurements of the radial component of a target’s velocity in relation to the radar. Doppler radars have applications in different industries including aviation, meteorology, healthcare and many others.
4. Monopulse radar
A monopulse radar is a radar system that compares the received signal from a single radar pulse against itself with an aim of comparing the signal as seen in multiple polarizations or directions. The most common form of monopulse radar is the adaptation of conical scanning radar which compares the return from two directions to directly measure the location of the target. It is important to note that most of the radars that were designed since the 1960s are monopulse radars.
5. Passive radar
A passive radar system is a type of radar that is designed to detect and track objects by processing reflections from non-cooperative sources of illumination in the environment. These sources include such things as communications signals and commercial broadcasts. Passive radar can be categorized in the same class of radar as bistatic radar.
6. Instrumentation radar
Instrumentation radars are radars that are designed to test rockets, missiles, aircrafts and ammunitions on government and private test ranges. They provide a variety of information including space, position, and time both in the real time and in the post processing analysis.
7. Weather radars
Weather radars are radar systems that are used for weather sensing and detection. This radar uses radio waves along with horizontal or circular polarization. The frequency selection of weather radar depends on a performance compromise between precipitation refection and attenuation as a result of atmospheric water vapor. Some weather radars are designed to use Doppler shifts to measure the speed of wind and dual polarization to identify precipitation types.
8. Mapping radar
Mapping radars are used to scan a large geographical region for geography and remote sensing applications. Because of their use of synthetic aperture radar, they are limited to relatively static objects. There are some specific radar systems that can sense humans behind walls thanks to the reflective characteristics of humans that are more diverse than the ones found in construction materials.
9. Navigational radars
Navigational radars are generally the same as search radars. However, they come with much shorter wavelengths that are capable of reflecting from the earth and from stones. They are mostly common on commercial ships and other long distance commercial aircrafts. There are various navigational radars that include marine radars commonly mounted on ships for collision avoidance and navigational purposes.
Phased-Array Radar Systems
These are newer, more sophisticated radar systems. A phased array means an electronically scanned array — a computer-controlled array of antennas which creates a beam of radio waves which can be electronically steered to point in different directions, without moving the antennas.
Phased arrays were invented for use in military radar systems, to scan the radar beam quickly across the sky to detect planes and missiles. These phased array radar systems are now widely used, and phased arrays are spreading to civilian applications. The phased array principle is also used in acoustics, and phased arrays of acoustic transducers are used in medical ultrasound imaging scanners (phased array ultrasonics), oil and gas prospecting (reflection seismology), and military sonar systems.
How Can You Learn More About Radar Technology?
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