What is Radar?

Radar stands for radio detection and ranging. It is a type of system which detects the distance, velocity, and angle of objects. This system can also detect weather formations, spacecraft, aircraft, missiles, terrain, etc.

How is Radar Used?

Radar systems consist of a transmitter that produces electromagnetic waves. To determine the properties of objects, a transmitting radar antenna, receiving radar antenna, processor, and receiver are used. The information about the location and speed of the object is determined by the radio waves that the transmitter emits, which reflect back off the object and return to the receiver.

In the period before World War II, this system was developed for military use by some countries secretly. In the United Kingdom, the cavity magnetron was the key development due to which development of small systems was allowed with sub-meter resolution.

Today, the uses of radar are wide-ranging. Some modern uses of radar include:

• Terrestrial and air traffic control
• Air defense systems
• Radar astronomy
• Marine radars to locate position and landmarks
• Ocean surveillance systems
• Aircraft anti-collision systems
• Outer space surveillance
• And more

High-tech radar systems are useful for extracting information from very high noise levels and are associated with machine learning and digital signal processing.

Principle of Radar

The principle of radar is the same as that of sound: it uses a short microwave signal. The distance of the targeted object can be directly calculated when the microwave is reflected from the object. Then, using that information, the direction can be calculated accurately. The data can be read on a visible screen.

Suppose a microwave is sent in a direction. It passes in a straight line, but when it hits an object, it reverts or reflects, and a part of this microwave is returned to its original position. This is generally called reflection. The principle behind the radar system is backscatter. It is directly proportional to the 6th power of the diameter of the target object and it is multiplied with its inherent properties of reflection. The wavelength should be larger than the particle diameter, which is also known as "Rayleigh scattering".

Structure of Radar

Components

A RADAR is a system composed of the following :

• The antenna unit, which consists of an antenna and motor. The motor rotates the antenna and the antenna transmits waves
• A transceiver unit that generates waves and processes the signal
• A processing unit, which processes the signal from the external devices and radar components
• The display unit, consisting of sensor data and a radar screen
• The control unit, which has all the radar controls

Basic Commands of Radar

Each radar component performs different operations, from the transmission to the display of information.

• Powerful microwave radiation is transmitted by the transceiver component as soon as the signal processing unit sends a trigger signal. With the help of a special tube called a waveguide, the microwaves are sent to the antenna, and the antenna re-emit it again.
• Over water, the emitted microwaves travel in a straight line. If this microwave encounters a hindrance in its path, then it informs about the presence of an object.
• The antenna receives several microwaves, which are transmitted through several circuits (frequency detection, signal amplification, and video detection). The signal is transformed in the antenna once the video is amplified and will be sent to the processor.
• The signals that are sent by the processor are transformed into visual data on a screen so that the user can easily interpret it.

Radar Antennas

X-Band Antennas

X-band antennas have shorter wavelengths. We know that the shorter the wavelength, the more the radio wave propagates in a straight line. This makes it easier to send waves in a direction and receive the reflected waves from the objects. This type of antenna is more precise and efficient when the wave is shorter. X-bands are economical, lightweight, and ergonomic since all components are compact.

S-Band Antennas

S-band antennas have longer wavelengths and have less attenuation, making it possible to detect distant targets. S waves are poorly reflected by the surface of the water, as they have low power and their reflection characteristics are poor. This is advantageous in the navigation process. They are used in concurrence with X -band radars.

L-Band Antennas

L-band radar is used in military applications operating at long-range high-frequency, from frequency band 1200-1400 MHz.

P-Band Antennas

The radar frequency range of P-band radar is between frequency band 225-390 MHz. It is mostly used in the case of remote sensing.

SAR Radar Antennas

SAR radar's antennas are another type of radar that are used for creating 2D and 3D reconstructions of landscapes. Processes that require night-sensing are done by SAR-type radar. The basis for radar interferometry is that the phase information can be measured minutely. A general phenomenon called speckle is caused by this type of radar. This speckle effect is due to the interaction of out-of-phase waves, which are reflected from the object.

InSAR Radar Antennas

InSAR stands for interferometric synthetic aperture radar. This interferometric SAR is used in remote sensing and geodesy.

NOTE: Radar can be deceived by using a device called electronic countermeasure (ECM). High-resolution radar uses wideband signals and SAR, which enhances the range and angular resolution of tracking.

Uses of Radar Sensors

We use radar sensors every day in different applications. These sensors are used for weather forecasts, vehicle systems, and traffic control systems. This type of sensor converts microwave echo signals into electrical signals. By figuring out objects' motion, shape, motion trajectory, and characteristics, they detect motion using wireless sensing technology.

Radar Reflectivity Measurement

The waves being returned to the radar from an object are termed reflectivity, and the phenomenon is termed as reflectance. Reflectivity measures the efficiency of an object to intercept and return radiofrequency energy on a large scale. The value of efficiency is provided by the radar system with which targeted objects return the energy transmitted by the radar, and this efficiency measurement is known as reflectivity.

Context and Applications

This topic is significant in the professional exams for undergraduate, graduate, and post-graduate courses such as:

• Bachelors in Technology
• Masters in Technology

Practice Problems

1. What does radar stand for?

1. Radio detection and ranging
2. Ration detection and range
3. Range and detection of radio
4. Radio and distance ranging

Answer: a

Explanation: The full form of radar is radio detection and ranging.

2. What can radar systems detect?

1. Distance, velocity, and angle
2. Distance, magnitude, and wavelength
3. Force, velocity, and distance
4. Torque, wavelength, and distance

Answer: a

Explanation: Radar systems are usually designed to detect the distance, velocity, and angle of objects.

3. What kind of waves are used in the radar system?

1. Infrared waves
2. X-ray waves
3. Radio or microwaves
4. None of these

Answer: c

Explanation: In the radar system, radio or microwaves, such as electromagnetic waves, are used.

4. By what range resolution of radar can be detected or determined?

1. Size of antenna
2. Power radiated from the antenna
3. Bandwidth of the transmitted pulse
4. Center frequency of the radar

Answer: c

Explanation: The resolution range of a radar depends on the width of the transmitted pulse, its type, size of the object, efficiency, and pulse width.

5. Which of the following is a practical application of radar?

1. Detection of aircraft
2. Telephone
3. Electron microscope
4. All of the above

Answer: a

Explanation: Radar is used in the detection of aircraft, for military purposes, etc.

Related Concepts

• Terrain-following radar
• Radar imaging
• Radar navigation
• Inverse-square law
• Wave radar