Automotive radars are used to detect the speed and range of objects in the vicinity of the car. Automotive radar consists of a transmitter and a receiver. The transmitter sends out radio waves that hit an object and bounce back to the receiver, determining the objects’ distance, speed and direction.
Application of Automotive radar and phased array signal processing to enhance automotive safety and simulate autonomous vehicles.
Automotive radar sensors can be classified into two categories: Short-Range Radar (SRR), and Long-Range Radar (LRR).
Short-range radar (SRR): Short-range radars (SRR) use the 24 GHz frequency and are used for short range applications like blind-spot detection, parking aid or obstacle detection and collision avoidance. These radars need a steerable antenna with a large scanning angle, creating a wide field of view.
The SRRs have been using the 24 GHz ISM band from 24.0 to 24.25 GHz with a bandwidth of 250 MHz, also called as the narrowband (NB). A bandwidth of 5 GHz, from 21.65 to 26.65 GHz – called as Ultra-Wideband (UWB) – is also available for automotive applications. But this UBW band will become obsolete by the year 2022 in both Europe and the U.S due to the Federal Communications Commission (FCC) and the European Telecommunications Standards Institute (ETSI) spectrum regularization.
24 GHz automotive radar systems are still ideal for tight budget constraints applications.
Long-range radar (LRR): Long-range radars (LRR) using the 77 GHz band (from 76-81GHz) provide better accuracy and better resolution in a smaller package. They are used for measuring the distance to, speed of other vehicles and detecting objects within a wider field of view e.g. for cross traffic alert systems. Long range applications need directive antennas that provide a higher resolution within a more limited scanning range. Long-range radar (LRR) systems provide ranges of 80 m to 200 m or greater.
Functioning of an Automotive Radar
An automotive radar chipset has multiple transmit and receive channels. The different transmit channels are used to drive different antennas (near and long range scans for instance). These multiple transmit channels also provides beam steering capabilities.
Multiple receive channels gives the angular information about the object as there is phase difference between signals received by different receive antennas.
We have seen most automotive companies and automotive radar chipset manufacturer’s move to the 77 GHz frequency band
Advantages of 77 GHz over 24 GHz for automotive radar systems:
1. Larger Available Bandwidth & Better Resolution: The 77 GHz frequency band for automotive radar applications uses the frequency range from 76 to 81 GHz with a bandwidth of over 4 GHz as compared to a bandwidth of 200 MHz available for automotive radar applications at 24 GHz. This wide bandwidth increases range and velocity resolution of the radar, allowing it to identify objects that are closely spaced, making these radars ideal for automated parking applications.
The differences in phase between the transmitted signal and the signal at the receiver to measure the relative velocity of an object. As the wavelength decreases, the resolution and accuracy of this velocity measurement improves proportionally. Therefore, as sensors move from 24 GHz to 77 GHz, velocity measurements can improve by 3x.
This enhanced resolution also improves the detection and avoidance of big objects, like cars, and allow the avoidance of smaller ones, like pedestrians, too. It also provide drivers with better object resolution in situations with poor visibility.
2. Smaller Size: 77 GHz radar systems are smaller in size in comparison to 24 GHz radars. As the relationship between the antenna size and the frequency is linear, the wavelength of 77 GHz signals is one-third of that of a 24 GHz system, therefore area needed for a 77 GHz radar antenna is one-ninth the size of a similar 24 GHz antenna.
3. Higher Power Levels: 77 GHz radars have higher permitted transmit power levels. The Effective Isotropic Radiated Power (EIRP) for automotive radars in the 77 GHz is 55 dBm (-3 dBm/MHz). For 24 GHz radars the peak limit is only 20 dBm EIRP.
These advantages are the main reason that we are seeing a shift to the 77 GHz band from the 24 GHz band.
Some Manufacturer of the same as below
Analog Devices- United States 
Infineon Technologies-Germany 
NXP Semiconductors-Netherlands 
STMicroelectronics-United State 
Acconeer AB – Sweden