Radar technology or RAdio Detection And Ranging, has come a long way since its inception in the early 20th century. Today, radar is an essential tool for weather prediction, air traffic control, and even self-driving cars. But how does radar work?
Radar works by sending out electromagnetic energy in the form of radio waves toward objects, commonly known as targets, and then detecting the replies. Targets may be aircraft, ships, or things as small as birds.
Put simply, it is a way to detect objects and determine their distance using radio waves.
Radar is also capable of determining the sizes and shapes of such objects, as well as their position, velocity, and presence. The ability of radar to detect faraway things under bad weather and measure their distance with accuracy distinguishes it from optical and infrared sensing instruments.
Radar is considered an “active” detecting device because it uses its own source of illumination (a transmitter) to find targets. It is generally used in the microwave band of the electromagnetic spectrum.
The frequency of each sound is measured in hertz (cycles per second), with frequencies ranging from 400 megahertz (MHz) to 40 gigahertz (GHz).
Radar Fundamentals
Radar is a device that transmits or “radiates” a narrow beam of electromagnetic energy into space from an antenna. A region where targets are anticipated is scanned by the tiny antenna beam.
When a target is illuminated by the beam, it absorbs some of the radiated energy and reflects a portion back toward the radar system. Because most radar systems do not transmit and receive at the same time, one antenna is frequently used for both transmission and reception on a time-sharing basis.
Basically, an antenna will transmit a signal and then quickly switch to listen and receive that signal.
The desired reflected signals are extracted by a receiver linked to the output element of the antenna and will hopefully reject those that are unimportant. For example, an aircraft’s echo might be of interest but not the rain which can possibly interfere.
The distance, or range, is calculated by adding the round-trip time for the radar signal to reach the target and return. The angular position of a target may be determined from the antenna’s orientation at the moment when the echo signal is received.
The target’s recent track can be determined by measuring the position of a target at successive instants of time. The future path of the target may then be predicted once this information is obtained.
Establishing a target’s track is vital in it actually being considered as a detected target.
It’s common for radars to employ a directive antenna, which directs its energy in a narrow beam. The beamwidth of a fixed-size antenna is inversely proportional to the radar frequency.
When the received echo is at its maximum, the direction of a target may be determined by noting which way the antenna is pointed.
The Monopulse method is used for determining the direction of a target, it is a precise technique that gathers data about the angle of a target. It’s calculated by comparing the amplitudes of signals received from two or more separate beams, each just a little off from the antenna’s main axis.
A radar system such as this might be used to detect the target’s position in both azimuth and elevation angles.
Doppler frequency and Target Velocity
Radar can detect the Doppler frequency shift of an echo generated by a moving target by comparing the received signal’s frequency to that of the transmitted signal.
If a moving target is approaching or receding from the radar, the echo signal’s frequency will rise or fall respectively.
A Doppler frequency shift is proportional to the target’s radial velocity, therefore a radar system that detects such a change in frequency can compute the target’s radial velocity.
Even when the echo signal from unwanted clutter is considerably greater than the echo from desired moving targets, the Doppler frequency shift can be used to identify moving targets from stationary ones.
A moving-target indication(MTI) radar or a pulse-Doppler radar is a form of pulse radar that uses the Doppler frequency shift to eliminate stationary clutter.
The Doppler frequency shift will be different for various parts of the target if the radar is moving relative to the target (as when a plane’s radar scans the ground). As a result, the Doppler frequency shift may allow the target’s various components to be distinguished.
Radar Imaging Understanding
Different types of targets can be detected by radar, and some systems are able to identify particular categories of targets, for example, a commercial plane as opposed to a military jet.
The ability to distinguish between objects is a key component of image analysis. The size and speed of the target are measured by viewing the target’s high-resolution image in one or more dimensions. Aircraft propellers and jet engines can assist in target identification because they modify the radar echo.
Radars are so sensitive that the distinctive modulation produced by the flapping of a bird’s wings in flight, may be utilized to identify that a bird is present or even to distinguish one kind of bird from another!
Synthetic aperture radar (SAR) is a type of radar that uses Doppler frequency to generate cross-range resolution, as well as range resolution. SAR generates an image of a scene that is comparable, but not identical, to an optical photograph using a synthetic aperture.
Each provides a different perspective. Because the frequencies at play are significantly higher, radar and optical pictures differ significantly.
SAR can operate from a very long range and through various atmospheric effects that limit optical and infrared imaging systems.
This is an advantage over passive optical imaging, which suffers from decreased resolution as range increases, SAR image’s resolution may be adjusted independently of range.
Components of a Radar
Antennas
The parabolic reflector is a widely adopted design of radar antenna. At the focal point of the parabola, a tiny antenna, such as a horn antenna, is located to illuminate the parabolic surface of the reflector.
The electromagnetic energy is radiated as a narrow beam after being reflected by this surface.
Transmitters
A radar system’s transmitter must be efficient, dependable, small as possible in size and weight, and simple to maintain. It should have a wide bandwidth and high power which are typical of radar applications.
The transmitter must produce low-noise, constant transmissions in order to avoid interfering (unwanted) signals from the transmitter with the detection of the small Doppler frequency shift produced by weak moving targets
Duplexer
An electronic device that allows bi-directional (duplex) communication over a single path. It will isolate the receiver from the transmitter while allowing them to share the same antenna.
Receivers
The radar receiver is a Superheterodyne, like most others. It must eliminate interference from extraneous echoes, as well as receiver noise, which obscures the target signals.
It must also boost the feeble received signals to a level where the receiver output is significant enough to drive a display or computer. The radar receiver technology is well understood, and it seldom has an effect on radar performance.
Signal and Data Processors
The receiver’s signal processor is the component that separates the desired target signal from other interference.
It’s not unusual for the discordant echoes to be a lot larger than the intended target echoes. It’s not uncommon for them to be 1 million times larger.
With computer technology, the majority of signal processing is done digitally. Digital signal processing has new potential in signal processing that analog techniques could not deliver.
Displays
The cathode-ray tube (CRT) has been the standard method for displaying information since the very early days of radar.
Flat-panel displays have, nevertheless, improved considerably owing to the demands of computers and televisions. Flat-panel displays take up less space and require less power than CRTs, but they have their own issues.
The Many Uses of Radar
There are many different types of radar, each with its own specific purpose. Here are some of the most common:
- Weather radars are used to track precipitation, such as rain and snow. It can also be used to detect other weather phenomena, such as thunderstorms and tornadoes.
- Air traffic control radar is used to track aircraft and ensure that they maintain a safe distance from each other.
- Ground-penetrating radar is used to map the subsurface of the earth. It can be used to locate underground utilities, caves, and even buried bodies.
- Police radar is used to detect speeding vehicles and issue traffic tickets.
- Military radar is used for a variety of purposes, such as tracking enemy aircraft and missiles.
- Space-based radar is used to track objects in orbit around the earth, such as satellites and space debris.
Conclusion
Radar technology has come a long way since its early days. It is now an essential tool for many different applications. From weather prediction to air traffic control, radar plays a vital role in keeping us safe and informed.