Roof-Top Antenna Cavity Could Replace Shark Fin Antennas in Cars

Today, cars enabled with high end communications technology, have become an important feature in the automotive industry. From helping guide users through satellite based navigation, to allowing them to make a call while driving. In the future, technology will not only play a greater role in road transport and mile to mile connectivity but also help improve road safety.

Antennas in cars are usually installed in what is known as the shark fin. This is a compact attachment that is mounted on the rear of the car’s roof. However, it is not possible to house a large number of antennas - a requirement for enabling high end communications of the future - in this kind of shark fin attachment. First of all, there is not enough space, and second, the antennas can interfere with one another when they are packed too tightly. This means that new options need to be found for housing antennas in cars.

Experts at TU Wien, thus have developed a special antenna box that can be integrated into the front area of the car roof. Detailed measurements show that the directionality of wireless signals is very good around cars, and with the new antenna variants cars are extremely well equipped for the wireless requirements of tomorrow.

This is problematic because the telecommunications capabilities of cars are expected to be significantly expanded in the coming years: in the future, cars can cooperate on the roads. A car would warn others of hazards, for example of a slippery patch after the next bend in the road. Communication between cars and fixed infrastructure is also expected, and even the ways in which communication between smartphones and vehicles could be utilized to improve road safety is being considered. With a mobile phone signal, the car could detect a pedestrian before they are even within view.

At TU Wien, the decision was therefore made to develop a new method for installing antennas in cars which overcame the upcoming technical challenges. Gerald Artner, an expert from the Telecommunications at TU Wien, constructed an antenna box from carbon-fibre-reinforced polymer material which could be installed in the front part of the roof, close to the windscreen.

The key question was whether antennas could actually be installed in the car’s roof and whether realistic measurement results across the entire vehicle were still comparable with the laboratory measured values. In cooperation with the Thüringer Innovationszentrum Mobilität [Thuringian Centre of Innovation in Mobility] at TU Ilmenau in Thuringia, this kind of antenna cavity was built into a car roof for the first time. The entire car was then surveyed in the only research laboratory of its kind in Europe, the Virtual Road Simulation and Test Area (VISTA), in order to identify the resulting radiation patterns.

According to Artner, they carefully analyzed the directions in which the antennas in their antenna cavity transmit, and the intensity thereof. As demonstrated, the antenna cavity not only provides more space for a larger number of antennas, but the directionality is also better than a ‘shark fin’ at the rear. The antennas in the ‘shark fin’ often do not provide high transmission power directly forwards because they are shielded by the curvature of the car roof. Artner’s antenna box gives excellent results right in this direction. It would also be possible to combine several antenna concepts in future cars. This would help compensate for any interference even more effectively. The results from TU Wien were published in the specialist journal ‘IEEE Antennas and Wireless Propagation Letters’.

Paper: G. Artner et al, Conformal Automotive Roof-Top Antenna Cavity With Increased Coverage to Vulnerable Road Users, IEEE Antennas and Wireless Propagation Letters, (2018)