Processing of Radar Signals 

Contents

•         Radar System
•         Radar Principle
•         Radar Signal Processing
•         Working
•         Doppler effect
•         Importance of RSP
•         Challenges in RSP
•         Application in RSP

What is Radar System?

A radar is an electromagnetic sensor that is used to find, track, and identify objects of various kinds at great distances. It works by sending electromagnetic radiation in the direction of what is called targets and then listening for the echoes that come back. The targets may include rain, birds, insects, ships, automobiles, astronomical bodies, and even aircraft and ships. Radar can occasionally determine the presence, location, and velocity of such objects in addition to their size and shape. The radar frequency range is from 30MHz to 100GHz. The capacity of radar to detect distant objects in inclement weather and to precisely calculate their range, or distance, sets it apart from optical and infrared sensing technologies.

What is Radar Signal Processing?

Radar signal processing is a technique and process used to extract valuable information from radar signals. A radar system's signal is released into the environment, where it moves and interacts with any objects it comes across. Some of the signals are returned to the radar system by these objects, where it is detected and examined.

The raw signals that the radar system receives are processed by radar signal processing to extract details on the position, speed, size, and other properties of the objects that are visible to the radar. This information can be used to track the movement of objects over time, identify different types of objects, and even image the surrounding environment

Radar Principle

Fig1. The basic principle of radar

The principle of radar involves sending out electromagnetic waves, measuring the reflected waves, and analyzing the received signals to determine the location and other characteristics of an object.

The electromagnetic signal is produced by the transmitter unit and is radiated in space by the radar antenna. While the receiver performs extraction of information from the signal received by the radar antenna.

What Is the Process of Radar Signal Processing?

Fig 2. Working of Radar Signal Processing

Radar signal processing works by analyzing the characteristics of the radar signal as it is received by the radar system. In order to extract information from the signal, signal processing algorithms employ methods including pulse compression, frequency modulation, and phase shifting.

A method for improving a radar system's range resolution is pulse compression. The radar can identify things that are closer together by achieving a higher resolution in range by compressing the pulse of the radar signal.

Another method utilized in the processing of radar signals is frequency modulation. It is possible to determine the velocity of the objects in the radar's area of vision by altering the frequency of the radar signal. This technique is commonly used in Doppler radar systems.

Phase shifting is a technique used to improve the accuracy of radar systems. By shifting the phase of the radar signal, it is possible to improve the resolution of the radar system in both range and angle.

Doppler Effect in Radar Signal Processing  

The Doppler effect is an important phenomenon in radar signal processing that is used to detect the velocity of objects in the radar's field of view. The Doppler effect occurs when there is a change in the frequency of a wave as a result of the motion of the source or the observer. In radar systems, the transmitted wave is reflected back by the object, and the frequency of the reflected wave is compared to the frequency of the transmitted wave. The difference in frequency is used to calculate the velocity of the object relative to the radar.

The Doppler effect is used in Doppler radar systems, which are commonly used in weather monitoring and air traffic control. These systems measure the velocity of moving objects, such as raindrops or aircraft, by detecting the frequency shift in the reflected radar signal. Doppler radar systems are also used in police radar guns to detect the velocity of moving vehicles.

When a radar signal encounters a moving object, the frequency of the signal is shifted by an amount proportional to the object's velocity. This frequency shift is known as the Doppler shift and is given by the equation:

Δf = 2fdv/c

where Δf is the Doppler shift, f is the frequency of the radar signal, d is the wavelength of the signal, v is the velocity of the object, and c is the speed of light.

Why is Radar Signal Processing Important?

Radar signal processing is important because it enables radar systems to detect and track objects accurately, making them effective in a variety of environments and conditions. The raw signals received by the radar system contain a lot of noise and interference, making it difficult to extract useful information about the objects in the radar's field of view. Signal processing techniques such as pulse compression, frequency modulation, and phase shifting are used to improve the signal-to-noise ratio and extract valuable information from the radar signals.

Grand Challenges in Radar Signal Processing

• Sparse Sensing Design in Radar- Sparse sensing is also known as compressed sensing (CS). Target detection, estimation, and classification issues have been successfully resolved in radar applications. In order to solve the underdetermined linear equations that describe many inverse problems, it mixes pseudorandom linear measurements and nonlinear reconstruction procedures.
• Radar Waveform Optimization- An emerging area in signal processing, waveform optimization for system parameter estimation has applications in radar and remote sensing. Radar waveform adaptation aims to dynamically enhance system performance in a variety of domains, including spatial, temporal, spectral, and polarisation.
• Cognitive Radar- Cognitive radar is a new and expanding field of study that has significant advantages for both military and commercial radar systems. Despite the fact that many research projects have concentrated on perception-action cycles, few of them have shown the learning component, and many areas of the subject still have unresolved issues. Potential advantages could come from a radar that uses online learning to carry out better actions and adjust its operational parameters in response to its situational awareness.
• Machine Learning for Radar- Machine learning (ML) has achieved great results which are attributed to major investments of many countries as well as massive cooperation among members of the international scientific community. In particular, the application of ML techniques has made it possible to enhance and get around the inherent limits of various signal processing methods based on conventional methods. The radar community has started to use ML techniques to solve common radar issues and approach enduring challenges from a fresh angle as a result of the success of doing so in many engineering domains.
• Coexistence of Radar and Communication Systems- Wireless communications have rapidly expanded in recent years, particularly for use in the Industrial Internet of Things (IIoT). Radar technology, on the other hand, has advanced in the direction of ever-increasing utility. Modern radar systems must be capable of changing the broadcast waveform and operating frequency band dynamically in response to the precise data that is continuously gathered from the immediate surroundings. The need for better and more flexible use of the spectrum is developing along with the demand for finite spectral resources, which is growing quickly.

Applications

•  Weather Forecasting -Radar systems are used in weather forecasting to detect precipitation and track the movement of storms. The radar signal processing algorithms used in weather radar systems are designed to analyze the characteristics of the reflected signals to estimate the intensity, location, and movement of precipitation. The Radar frequency weather forecasting of 30 MHz to 40GHz.

Fig 3. Weather Forecasting

• Air Traffic Control - Radar systems are used in air traffic control to track the position, altitude, and speed of aircraft in flight. The radar signal processing algorithms used in air traffic control systems are designed to filter out clutter and noise to accurately detect and track aircraft. The Radar frequency of air traffic control is from 30MHz to 3GHz. 

Fig 4. Air Traffic Control

Military Surveillance - Radar systems are used in military surveillance to detect and track ground and air-based targets. The radar signal processing algorithms used in military radar systems are designed to detect small, fast-moving targets in cluttered environments and to identify targets based on their size, shape, and movement pattern. The Radar frequency of military surveillance is from 300MHz to 40GHz. 

Fig 5. Military Surveillance

Missile Defense - Radar systems are used in missile defense to detect and track incoming missiles. The radar signal processing algorithms used in missile defense systems are designed to quickly detect and track fast-moving targets in cluttered environments and to calculate the trajectory of the missile to determine the best course of action for intercepting it. The Radar frequency of military surveillance is from 2GHz to 12GHz. 

Fig 6. Missile Defense System

•  Autonomous Vehicles - Radar systems are used in autonomous vehicles to detect and track other vehicles, pedestrians, and obstacles in the environment. The radar signal processing algorithms used in autonomous vehicle radar systems are designed to filter out noise and interference to accurately detect and track objects in real time. The Radar frequency of autonomous vehicles is from 24 GHz to 77 GHz.

Fig 7. Autonomous Vehicles System

•  Industrial Process Control - Radar systems are used in industrial process control to measure the level of fluids in tanks and vessels. The radar signal processing algorithms used in industrial radar systems are designed to accurately measure the level of fluids in tanks and vessels regardless of the fluid type, temperature, or pressure. The Radar frequency of Industrial Process Control is from 6 GHz to 26 GHz.

•  Geological Surveying - Radar systems are used in geological surveying to map the subsurface of the earth. The radar signal processing algorithms used in geological radar systems are designed to detect and analyze the reflected signals to identify subsurface features such as rock layers, fault lines, and mineral deposits. The Radar frequency of Geological Surveying is from 10 MHz to 2.6 GHz.

Fig 8. Geological Surveying

Conclusion - 

To summarise, radar signal processing is an essential part of modern radar systems that enables them to detect, track, and recognize objects in their environment. Radar systems can efficiently operate in a variety of applications by extracting useful information from the signals they receive using complex algorithms and procedures.

Written by 

Mohish Khadse, Sakshi Kulkarni, Sejal Sayam & Shjjad Shaikh.