Radar technology in vehicles plays a pivotal role in enhancing safety, comfort, and convenience for drivers and passengers alike.  By utilizing electromagnetic waves to detect objects and obstacles in the vehicle's vicinity, radar systems provide critical information to onboard computer systems, enabling a range of advanced driver assistance features. These include adaptive cruise control, which automatically adjusts vehicle speed to maintain a safe distance from the vehicle ahead, collision avoidance systems that provide warnings or intervention to prevent accidents, and parking assistance systems that aid drivers in maneuvering into tight spaces with precision. By integrating radar sensors into vehicles, manufacturers can significantly reduce the likelihood of accidents, improve overall driving experiences, and pave the way for the development of autonomous driving technologies in the future. Automotive radars operate on specific frequency bands. Over time, a significant transition has taken place, moving from the traditional 24 GHz band to the more advanced and flexible 77 GHz band. This article explores the reasons behind this shift and sheds light on the advantages of the 77 GHz band over the 24 GHz band.

Frequency Bands Dedicated to Automotive Radars

Automotive radars primarily use four frequency bands globally, including the 24 GHz and 77 GHz bands. The table below summarizes these bands, highlighting their respective characteristics:

Frequency (GHz)	Bandwidth	Type of Band
24 to 24.25 GHz	250 MHz	ISM Band
21 to 26 GHz	5 GHz	UWB (Ultra Wide Band)
76 to 77 GHz	1 GHz	LRR (Long Range Radar) Band for Automotive
77 to 81 GHz	4 GHz	SRR (Short Range Radar) Band for Automotive

Transition in Europe

The 24 GHz band had been temporarily used for automotive radars in Europe for collision avoidance and other safety applications. However, due to increasing demand for spectrum and regulatory changes, further use of the 24 GHz band for automotive radars is no longer feasible.

The FCC (Federal Communications Commission) in the United States and the European Telecommunications Standards Institute (ETSI) have imposed spectrum regulations that affect the use of the 24 GHz band for automotive radars. These regulations may restrict or phase out the use of the 24 GHz band for automotive radar applications.

In response to these regulatory changes, the European Commission has proposed transitioning to the 77 GHz band for automotive radars as a replacement for the 24 GHz band. The 77 GHz band is internationally available and offers several advantages over the 24 GHz band, making it perfectly adequate for automotive radar applications.

Advantages of the 77 GHz Band Over 24 GHz for Automotive Radars

1. Larger Available Bandwidth & Better Resolution

The 77 GHz frequency band for automotive radar applications covers the range from 76 to 81 GHz, with a bandwidth of over 4 GHz, compared to a 200 MHz bandwidth available for automotive radar applications at 24 GHz. This wider bandwidth enhances radar range and velocity resolution, enabling the identification of closely spaced objects, making these radars ideal for automated parking applications.

As sensors shift from 24 GHz to 77 GHz, velocity measurements can improve by a factor of 3, thanks to differences in phase between the transmitted and received signals.

This enhanced resolution also improves the detection and avoidance of larger objects like cars and allows the avoidance of smaller ones, such as pedestrians. It provides drivers with better object resolution in situations with poor visibility.

2. Smaller Size

77 GHz radar systems are smaller than their 24 GHz counterparts are. The linear relationship between antenna size and frequency means that the wavelength of 77 GHz signals is one-third of that of a 24 GHz system. As a result, the 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 band is 55 dBm (-3 dBm/MHz), whereas, for 24 GHz radars, the peak limit is only 20 dBm EIRP.

These advantages are the main reasons for the shift from the 24 GHz band to the 77 GHz band.

Use case: South Africa

In South Africa, the regulatory authorities have designated specific frequency bands for vehicle radar systems to ensure efficient and safe operation on the road. These bands include 24.05 - 24.075 GHz, 24.075 - 24.15 GHz, and 24.75 - 24.25 GHz, catering to various automotive radar applications such as adaptive cruise control, collision avoidance, and parking assistance. Additionally, the country allows the use of the 76-77GHz band, known for its high-resolution sensing capabilities, further enhancing the effectiveness of radar-based safety features in vehicles. By allocating these frequency bands, South Africa aims to facilitate the adoption of advanced radar technologies in vehicles, contributing to improved road safety and driving experiences across the country.

The following table shows the bands allowed by ICASA for Road Transport and Traffic Telematic applications:

Frequency Band	Maximum Power	Harmonized Standard
24.05-24.075 GHz	100 mW e.i.r.p.	EN 300 440
24.075-24.15 GHz	0.1 mW e.i.r.p.	EN 300 440
24.15-24.25 GHz	100 mW	EN 300 440
76-77 GHz	55 dBm peak e.i.r.p.	EN 301 091
77-81 GHz		EN 302 264

In a nutshell, radar technology in vehicles has revolutionized automotive safety and comfort, paving the road for a new era of advanced driver assistance features. From adaptive cruise control to collision avoidance and parking assistance systems, radar sensors have become indispensable components in modern vehicles, enhancing driver awareness and reducing the risk of accidents.

The transition from the traditional 24 GHz band to the more resourceful 77 GHz band represents a significant milestone in the evolution of automotive radar technology. With wider bandwidth, better resolution, smaller size, and higher power levels, the 77 GHz band offers numerous advantages over its predecessor, enabling more precise and efficient radar sensing capabilities. Moreover, regulatory authorities worldwide, including South Africa, have recognized the importance of allocating specific frequency bands for vehicle radar systems, ensuring safe and efficient operation on the road.

By embracing advanced radar technologies and regulatory frameworks, countries can continue to improve road safety and driving experiences for motorists across the globe, leading the way for a safer and more connected future on our roads.