The full form of RADAR is Radio Detection And Ranging. It is an umbrella term for any remote sensing device used to detect the presence, position, size and speed of objects with the help of radio waves.
The development of RADARs was spread out over several years between the late 1800s and mid-1900s. Similar variations of the technology were developed independently by many countries around the same time. Hence, it is difficult to accredit the invention to an individual researcher or a group of researchers.
Having said that, the contribution of Maxwell, Hertz, Marconi, Hülsmeyer and Watt is considered quite significant in the field.
RADAR’s full form tells us that the technology is concerned with detecting objects with radio waves. Similar to how we see objects after they get illuminated by light with the help of our eyes, RADARs use a combination of transmitter and receiver to ‘see’ what’s around them.
The transmitter emits the radio waves in the direction of the target in the form of continuous signals or intermittent pulses. The waves travel through the medium in which the RADAR system and the target is present until they finally hit the target and get reflected as an echo.
The reflected waves travel back to their source and are detected by a receiver. This not only tells us that an object is present in the line of sight but also gives us an idea about how far it is. Since the speed of propagation of radio waves in various media is already known, by measuring the time delay between the transmission and reception of the radio waves, the distance between the source and target can be computed.
Only a fraction of radio waves are picked up by the receiver as most of the energy is lost either during propagation or due to scattering. The is the reason why RADARs need a powerful transmitter, a sensitive receiver and a capable digital signal processor to function properly.
In addition to finding out how far the objects are, RADARs can also be used to determine how fast the objects are moving towards or away from the signal source. When we transmit radio waves at an object that is moving towards us, the reflected radio waves tend to get compressed, causing an increase in their frequency. The effect is the opposite in case if the object is moving away from us. This phenomenon is known as the doppler effect and helps us calculate the speed of moving objects by observing a change in the frequency of radio waves during the process.
Since the complete working of a RADAR is based on the measurement of time delay between sending and receiving the signal, it is critical for the transmitter and receiver to be in proper sync, which requires sophisticated control equipment.
In practice, RADARs need to be designed after carefully considering the required resolution and range. Radio waves at high frequencies offer excellent resolution but are susceptible to attenuation and scattering, which limits their range. On the other hand, low-frequency radio waves have a higher range but have poor resolution. It’s a trade-off between range and resolution that engineers need to make based on the requirements of the particular application the design is being made for.
A surprisingly large number of applications of RADARs exist. As the technology has been around for a long time now, it has become a reliable, economical, efficient and commonly available technology for detecting objects from a distance.
Air Trafic Control: RADARs are used in both passenger aircraft and ground control stations for navigation purposes. The technology also warns the pilots and air traffic control about extreme or unfavourable weather conditions.
Military applications: Fighter jets use RADAR to find out their altitude and detect the presence of any other physical structure or aircraft nearby. RADARs are also used in ships and submarines for navigation and the detection of mines.
Applications in Automobiles: Autonomous vehicles use RADAR and other technologies like LIDAR and cameras as sensors to create a virtual 3D profile of their surroundings. Usually, high-frequency RADARs are used in cars as accuracy is the priority over range. These devices are the eyes of autonomous vehicles. To read more about the similarities and differences between LIDAR and RADAR, check out our article on LIDAR vs. RADAR: Detection, Tracking, and Imaging. Alternatively, you can read our report on Autonomous Vehicle Technology to know about the latest trends in the autonomous vehicle industry.
Speed cameras: On roads, RADAR speed cameras and handheld RADAR detectors can be used to keep the speed of vehicles in check.
Apart from the applications mentioned above, RADARs are also extensively used in space research, weather forecasting, and numerous other remote sensing applications.
Even though the applications of RADAR span several different systems of different sizes, the basic principle behind the working of the technology remains the same.
Back when RADAR systems were first developed, operating them was extremely complicated. The operator had to manually tune the operating frequency based on the environmental conditions to reduce the noise. The advancements in Artificial Intelligence and Digital Signal Processing have made it possible to automate a lot of things that previously required human intervention. Cognitive RADARs learn from their experiences to adapt to the environment and improve performance over time. Cognitive RADAR along with phased array RADARs are the future and among the hottest areas of research in signal processing.
The advancements in RADAR and its integration with other notable detection technologies is all set to revolutionise remote sensing forever. This will open up a whole new world of possibilities and applications in various different fields of engineering.
 Scheer, J. (2012). Principles of Modern Radar: Advanced Techniques, Volume 2. United Kingdom: Institution of Engineering and Technology.
 Michael Parker, Chapter 16 - Radar Basics, Editor(s): Michael Parker, Digital Signal Processing 101, Newnes, 2010, Pages 191-200, ISBN 9781856179218, https://doi.org/10.1016/B978-1-85617-921-8.00020-1.
 H. Zhu, Z. Zhu, F. Su and J. Zhang, "New Algorithms in Cognitive Radar," 2018 11th International Congress on Image and Signal Processing, BioMedical Engineering and Informatics (CISP-BMEI), 2018, pp. 1-4, doi: 10.1109/CISP-BMEI.2018.8633239.
 Fenn, Alan & Temme, Donald & Delaney, William & Courtney, William. (2000). The Development of Phased-Array Radar Technology. Lincoln Lab. J.. 12.