Advantages of 77 GHz Automotive Radars over 24 GHz Systems

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- everything RF

Aug 13, 2019

Automotive radars operate at both 24 GHz and 77 GHz. However over the last few years most automotive companies and automotive radar chipset manufacturers have started to move to the 77 GHz frequency band. In this article we have highlighted a few advantages of the 77 GHz frequency band for automotive radar systems over 24 GHz radars.

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.