We can observe different objects around the world. Similarly, radar-like radio detection and ranging is used to assist the pilots while flying through fog because the pilot cannot notice that where they are traveling. The radar used in the airplanes is similar to a torchlight that works with radio waves in place of light. The airplane transmits a blinking radar signal and listens out for any indications of that signal from nearby objects. Once the indications are noticed, then the airplane identifies something is near & it uses the time taken for the indications to reach for discovering how distant away it is. This article discusses an overview of Radar and its working.
Who Invented Radar?
Similar to several inventions, the radar system is not easy to give credit to an individual because it was the outcome of earlier work on the properties of electromagnetic radiation for the accessibility of numerous electronic devices. The question of main concern is more complicated by the hide of military privacy under which radio location techniques were examined in different countries in the early days of World War-II.
This review writer finally concluded that when radar system is a clear case of direct creation, Robert Watson-Watt’s note on Aircraft’s Detection & Location of by Radio Methods published immediately 50 years ago. So it was the most significant solitary publication in this field. British achievement in the fight of Britain allocated much to the expansion of a radar system that included technical growth with operational feasibility.
What is a Radar System?
RADAR stands for Radio Detection and Ranging System. It is basically an electromagnetic system used to detect the location and distance of an object from the point where the RADAR is placed. It works by radiating energy into space and monitoring the echo or reflected signal from the objects. It operates in the UHF and microwave range.
A radar is an electromagnetic sensor, used to notice, track, locate, and identify different objects which are at certain distances. The working of radar is, it transmits electromagnetic energy in the direction of targets to observe the echoes and returns from them. Here the targets are nothing but ships, aircraft, astronomical bodies, automotive vehicles, spacecraft, rain, birds, insects, etc. Instead of noticing the target’s location and velocity, it also obtains their shape and size sometimes.
The main objective of radar as compared with infrared and optical sensing devices is to discover faraway targets under difficult climate conditions & determines their distance, range, through precision. Radar has its own transmitter which is known as a source of illumination for placing targets. Generally, it works in the microwave area of the electromagnetic spectrum that is calculated in hertz when frequencies extend from 400 MHz to 40 GHz. The essential components which are used in the radar
Radar undergoes quick development during the years 1930-the 40s to reach the requirements of the military. It is still broadly used through the armed forces, wherever several technological advances have created. Simultaneously, radar is also utilized in civilian applications particularly in controlling air traffic, observation of weather, navigation of ship, environment, sensing from remote areas, observation of planetary, measurement of speed in industrial applications, space surveillance, law enforcement, etc.
The radar working principle is very simple because it transmits electromagnetic power as well as examines the energy returned back to the target. If the returned signals are received again at the position of their source, then an obstacle is in the transmission way. This is the working principle of radar.
Fundamentals of Radar
The RADAR system generally consists of a transmitter that produces an electromagnetic signal which is radiated into space by an antenna. When this signal strikes an 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 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 the maximum amplitude echo signal, the antenna points to. To measure the range and location of moving objects, the Doppler Effect is used.
The essential parts of this system include the following.
- 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 the transmitter is working.
- Receiver: It can be a superheterodyne 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.
How Does Radar use Radio?
Once the radar is placed on a ship or plane, then it requires a similar essential set of components to produce radio signals, transmit them into space and receive them by something, and finally display the information to understand it. A magnetron is one kind of device, used to generate radio signals which are used through radio. These signals are similar to light signals because they travel at the same speed but their signals are much longer with fewer frequencies.
The light signals wavelength is 500 nanometers, whereas the radio signals used by radar normally range from centimeters to meters. In an electromagnetic spectrum, both the signals like radio and light are made with variable designs of magnetic and electrical energy throughout the air. The magnetron in radar generates microwaves the same as a microwave oven. The main disparity is that the magnetron within radar has to transmit the signals several miles, rather than just small distances, so it is more powerful as well as much larger.
Whenever the radio signals have been transmitted, then an antenna functions as a transmitter to transmit them into the air. Generally, the antenna shape is bent so it mainly focuses the signals into an exact and narrow signal; however radar antennas also normally revolve so they can notice actions over a huge area.
The radio signals travel outside from the antenna with 300,000 km per second speed until they strike something and some of them return back to the antenna. In a radar system, there is an essential device namely a duplexer. This device is used to make the antenna change from side to side in between a transmitter & a receiver.
Types of Radar
There are different types of radars which include the following.
This type of radar system includes a Tx-transmitter & an Rx- receiver that is divided through a distance that is equivalent to the distance of the estimated object. The transmitter & the receiver are situated at a similar position is called a monastic radar whereas the very long-range surface to air & air to air military hardware uses the bistatic radar.
It is a special type of radar that uses the Doppler Effect to generate data velocity regarding a target at a particular distance. This can be obtained by transmitting electromagnetic signals in the direction of an object so that it analyzes how the action of the object has affected the returned signal’s frequency.
This change will give very precise measurements for the radial component of an object’s velocity within relation toward the radar. The applications of these radars involve different industries like meteorology, aviation, healthcare, etc.
This kind of radar system compares the obtained signal using a particular radar pulse next to it by contrasting the signal as observed in numerous directions otherwise polarizations. The most frequent type of monopulse radar is the conical scanning radar. This kind of radar evaluates the return from two ways to measure the position of the object directly. It is significant to note that the radars which are developed in the year 1960 are monopulse radars.
This kind of radar is mainly designed to notice as well as follow the targets through processing indications from illumination within the surroundings. These sources comprise communication signals as well as commercial broadcasts. The categorization of this radar can be done in the same category of bistatic radar.
These radars are designed for testing aircraft, missiles, rockets, etc. They give different information including space, position, and time both in the analysis of post-processing & real-time.
These are used to detect the direction and weather by using radio signals through circular or horizontal polarization. The frequency choice of weather radar mainly depends on a compromise of performance among attenuation as well as precipitation refection as an outcome of atmospheric water steam. Some types of radars are mainly designed to employ Doppler shifts to calculate the wind speed as well as dual-polarization to recognize the types of rainfall.
These radars are mainly used to examine a large geographical area for the applications of remote sensing & geography. As a result of synthetic aperture radar, these are restricted to quite stationary targets. There are some particular radar systems used to detect humans after walls that are more different as compared with the ones found within construction materials.
Generally, these are the same to search radars but, they available with small wavelengths that are capable of replicating from the ground & from stones. These are commonly used on commercial ships as well as long-distance airplanes. There are different navigational radars like marine radars which are placed commonly on ships to avoid a collision as well as navigational purposes.
Pulsed RADAR sends high power and high-frequency pulses towards the target object. It then waits for the echo signal from the object before another pulse is sent. The range and resolution of the RADAR depend on the pulse repetition frequency. It uses the Doppler shift method.
The principle of RADAR detecting moving objects using the Doppler shift works on the fact that echo signals from stationary objects are in the same phase and hence get canceled while echo signals from moving objects will have some changes in phase. These radars are classified into two types.
It transmits high pulse repetition frequency to avoid Doppler ambiguities. The transmitted signal and the received echo signal are mixed in a detector to get the Doppler shift and the difference signal is filtered using a Doppler filter where the unwanted noise signals are rejected.
Moving Target Indicator
It transmits low pulse repetition frequency to avoid range ambiguities. In an MTI RADAR system, the received echo signals from the object are directed towards the mixer, where they are mixed with the signal from a stable local oscillator (STALO) to produce the IF signal.
This IF signal is amplified and then given to the phase detector where its phase is compared with the phase of the signal from the Coherent Oscillator (COHO) and the difference signal is produced. The Coherent signal has the same phase as the transmitter signal. The coherent signal and the STALO signal are mixed and given to the power amplifier which is switched on and off using the pulse modulator.
The continuous wave RADAR doesn’t measure the range of the target but rather the rate of change of range by measuring the Doppler shift of the return signal. In a CW RADAR electromagnetic radiation is emitted instead of pulses. It is basically used for speed measurement.
The RF signal and the IF signal are mixed in the mixer stage to generate the local oscillator frequency. The RF signal is then transmitted signal and the received signal by the RADAR antenna consists of the RF frequency plus the Doppler shift frequency. The received signal is mixed with the local oscillator frequency in the second mixture stage to generate the IF frequency signal.
This signal is amplified and given to the third mixture stage where it is mixed with the IF signal to get the signal with Doppler frequency. This Doppler frequency or Doppler shift gives the rate of change of range of the target and thus the velocity of the target is measured.
Radar Range Equation
There are different kinds of versions available for the radar range equations. Here, the following equation is one of the fundamental types for an only antenna system. When the object is assumed to be in the middle of the antenna signal, then the highest radar detection range can be written as
Rmax = 4√Pt λ2G2σ/(4π)3Pmin
= 4√Pt C2G2σ/fo2(4π)3Pmin
‘Pt’ = Transmit power
‘Pmin’ = Minimum detectable signal
‘λ’ = Transmit wavelength
‘σ’ = Cross-section of the target radar
‘fo’= Frequency in Hz
‘G’ = Gain of an antenna
‘C’ = Light speed
In the above equation, the variables are stable as well as rely on radar apart from the target like RCS. The order of transmit power will be 1 mW (0 dBm) & the gain of antenna approximately 100 (20 dB) for an ERP (efficient radiated power) of 20 dBm (100 mW). The order of least noticeable signals are picowatts and the RCS for a vehicle might be 100 square meters.
So, the radar range equation’s exactness will be the input data. Pmin (minimum noticeable signal) mainly depends on the bandwidth of receiver (B), F (noise figure), T (temperature) & necessary S/N ratio (signal-to-noise ratio).
A receiver with narrow bandwidth will be more responsive as compared with a wide BW receiver. Noise figure can be defined as; it is a calculation of how much noise the receiver can contribute toward a signal. When the noise figure is lesser then the noise will be less the device donates. When the temperature increases, it will affect the sensitivity of the receiver through rising input noise.
Pmin = k T B F (S/N)min
From the above equation,
‘Pmin’ is the least detectable signal
‘k’ is the Boltzmann’s constant like 1.38 x 10-23 (Watt*sec/°Kelvin)
‘T’ is a temperature (°Kelvin)
‘B’ is the bandwidth of a receiver (Hz)
‘F’ is the Noise Figure (dB), Noise Factor (ratio)
(S/N) min = Least S/N Ratio
The i/p thermal noise power which is available can be proportional toward the kTB wherever ‘k’ is Boltzmann’s constant, ‘T’ is temperature and ‘B’ is the bandwidth of receiver noise in hertz.
T = 62.33°F or 290°K
B = 1 Hz
kTB = -174 dBm/Hz
The above radar range equation can be written for received power like a range of function for a provided transmit power, antenna gain, RCS & wavelength.
Prec = Pt λ2G2σ/(4π)3R4max = Pt C2G2σ/(4π)3R4fo2
Prec = PtG2(λ/4π)2 σ/4πR2
From the above equation,
‘Prec’ is the received power
‘Pt’ is the transmit power
‘fo’ is the transmit frequency
‘λ’ is the transmit wavelength
‘G’ is the gain of an antenna
‘σ’ is the cross-section of radar
‘R’ is the range
‘c’ is the speed of light
The applications of radar include the following.
It has 3 major applications in the Military:
- In air defense, it is used for target detection, target recognition, and weapon control (directing the weapon to the tracked targets).
- In a missile system to guide the weapon.
- Identifying enemy locations on the map.
Air Traffic Control
It has 3 major applications in 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
It can be used for observing whether or observing planetary positions and monitoring sea ice to ensure a smooth route for ships.
Ground Traffic Control
It can also be used by traffic police to determine the speed of the vehicle, controlling the movement of vehicles by giving warnings about the presence of other vehicles or any other obstacles behind them.
It has 3 major applications
- To guide the space vehicle for a safe landing on the moon
- To observe the planetary systems
- To detect and track satellites
- To monitor the meteors
Summary Radar is something that is in use all around us, although it is normally invisible. ATC (Air Traffic Control) uses radar to track planes both on the ground and in the air, and also to guide planes in for smooth landings. Police use radar to detect the speed of passing motorists. NASA uses radar to map the Earth and other planets, to track satellites and space debris and to help with things like docking and maneuvering. The military uses it to detect the enemy aircraft, ships, submarines and to guide weapons.