Connected car design requires practical antenna considerations

The connected car is becoming increasingly connected. Each new model year takes big steps forward, offering a growing list of options such as advanced safety features and emerging DSRC radios for talking to other cars and roadside infrastructure, as the industry moves to the not-so-distant future of autonomous vehicles. With each new connected car advancement comes the need for a new antenna. However, the automotive industry’s requirement for more antennas to deliver the high-bandwidth, low-latency connectivity required for advanced services is seemingly at odds with two key requirements of vehicle manufacturers. The first is the need for a more simplistic way to locate antennas in the vehicle to maximise performance, minimise interference and reduce installation costs; the second is the search for a reduction in the number of cables and connectors that can cause noise and vibrations, and are complicated and expensive to install. As the number of individual radio systems in vehicles grows, achieving these objectives calls for a new, elegant design strategy that takes into account both vehicle aesthetics and advanced technical requirements. One of the biggest challenges that vehicle manufacturers face in terms of creating the next generation of connected car is getting the volume of antennas needed to power the vehicle to work efficiently in such a small space – and at a competitive cost – while minimising interference and maximising performance Cables and Connectors Running cables from the radios to their antennas is expensive and difficult from a design perspective. A common solution is to locate the radios together in a Telematics Control Unit (TCU), and place that close to where the antennas are located. One of the trade-offs enabled by this strategy is that the antennas for the radios in question often need to be remotely mounted elsewhere in the car to have an appropriate radiation pattern to communicate with the other end of the radio link. This type of set-up has numerous additional effects. First, inexpensive digital communication wiring can replace coax cable between the TCU and the rest of the car systems. Second, active antennas can be eliminated because the transmission lines between radio and antenna are short, making their losses negligible. Third, there is a greater possibility for interference between the radio systems when antennas are co-located, and so this must be accommodated in design. And finally, when radio electronics are co-located near their antennas, there is more opportunity for RF emissions from those electronics to interfere with radio reception performance. Additional design effort and testing is required. The co-location of TCU electronics and antennas also requires a new way of thinking about RF interconnects. A short coax cable could be used to connect the TCU radios and antennas; however, each of these potential eight to ten connectors between the radio and antenna is a potential long-term failure point in the high-vibration environment of a moving vehicle. In addition, each connector represents the potential for assembly errors as well as costly labour for installation. A standardised solution for this application is being researched by connector and antenna companies. One of the most promising research areas is the use of selective axis of conduction elastomer materials to create PCB board-to-board interconnects with what looks like a simple layer of rubber. Issues such as insertion losses, isolation and cross-talk still need resolution, but the concept looks promising. Antennas Connected cars require high-speed internet connections for several reasons today, including eCall, vehicle diagnostics and software updates. Autonomous vehicles will take that connectivity requirement to a whole new level, requiring consistent access to high-speed, reliable, low-latency connectivity to be able to deliver safety-critical applications such as vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications. One of the biggest challenges that vehicle manufacturers’ RF teams face in terms of creating the next generation of connected car is getting the volume of antennas needed to power the vehicle to work efficiently in such a small space – and at a competitive cost – while minimising interference and maximising performance. Added to that complexity is the fact that every make and model has different space and size configuration, making a one-size-fits-all solution for antenna placement more difficult. Custom antenna solutions required for testing different scenarios, however, can be expensive and take time to develop and deliver. Most antennas will be placed into a single area of the car, and the antenna deployment area will take up more space. But how does that reconcile with the sleek interiors of vehicles to which car designers and customers are accustomed? Other factors to consider when installing antennas for the connected car, include antenna size (more antennas will be required in the same size ‘fin’), the necessary requirements to reduce EMC and frequency interference, including unique design elements and manufacturing methods; accounting for the harsh environment in which vehicles operate (extremely high and low temperatures); and the impact of noise and vibrations from bumpy roads and engine noise (for which PCB surface-mount antennas are emerging as a practical way to deal with these challenges). The cost, weight, complexity and RF performance benefits of co-locating the radio and antenna far outweigh the added design and development complexity, however. Most antennas will be placed into a single area of the car, and the antenna deployment area will take up more space. But how does that reconcile with the sleek interiors of vehicles to which car designers and customers are accustomed? Considerable effort is being made to better understand the complex interaction between the volume of antennas and radios in close proximity. Some antenna companies are well along the path of solving these challenges based on their work in other markets, and have mapped out best practices for antenna placement in relation to their radios and to each other. Wanted: digital interface standard While it would be nice to be able to put the vehicle antennas into a single package, a few such as AM/FM antennas may still need to be located a distance away from the main antenna cluster and linked with coax. Cellular antennas need to be physically separated to ensure maximum multiple input multiple output (MIMO) throughput performance. The radios, however, can still be integrated into the TCU and the antenna located nearby. By working with vehicle manufacturers, antenna manufacturers are leading the charge to enable the next generation of connected car Longer term, a digital interface standard should be created to allow the radios to be integrated directly with their antenna. This would allow the radio and antenna units to be placed anywhere in the vehicle that meets the radio’s performance need while also minimising coax cable and RF interconnects, thereby simplifying installation and reducing cost. The connections would be limited to high-speed digital data and power, and the lower cost wiring and connectors involved. Vehicle manufacturers and Tier 1 suppliers are moving quickly to bring increasingly connected vehicles to market. Cables, connectors and antennas play a critical role in advancing the timelines of these vehicles. By working with vehicle manufacturers to overcome the challenges associated with the design and placement of antennas, cables and connectors in this delicate environment, antenna manufacturers are leading the charge to enable the next generation of connected car. About the author: Dan Michael is Director of Automotive at Taoglas

Connected car design requires practical antenna considerations

Antenna manufacturers are leading the charge to enable the next generation of connected car, writes Dan Michael

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