Multiple antennas a requirement for new cars
The new features of automotive interiors come at a cost of multiple sets of wireless information and content being delivered transparently to the driver. In the past, this was at most two antennas - AM and FM for the entertainment system. Modern vehicles need a few more antennas, and the count is growing.
A typical high-end car today has AM, FM, Satellite Radio, TPM, Remote Entry, Remote Start, In-Vehicle TV, DAB, GPS, Bluetooth, Collision Avoidance Radar, Parking Assist Radar and Electronic Toll Collection. Next-gen vehicles will add GSM and LTE in addition to Wi-Fi, specialized Car-To-Car Communications and additional systems for automated drivers assist.
One of the challenges of these systems is directionality of the antenna and its ability to pick up the signal with the vehicle facing different directions. The nominal solution for this issue is the use of a diversity system that employs multiple antennas and then has circuitry to determine which one has the strongest signal, and then use that one.
However with the large number of antennas needed in the system - over 15 now and quickly approaching 20 - initial placement of these antennas in a non-interfering manner on the vehicle is a big challenge. This is even before the duplicating of the antennas to support the diversity requirements.
The antennas are still passive, but have migrated from Mast/Whip antennas, to glass-mount antennas to the new generation bee sting antenna designs and the shark fin modules. These are being used with a combination of the glass-mount antennas and new distributed antennas. As the frequency diversity increases more shapes of antennas are needed, as shown in the table below (courtesy of Intech):
Companies like Delphi àre developing new multi-antenna modules that fit into the new standard shark fin shape and can address several of the RF requirements including soon-to-be released LTE support (figure below, courtesy of Continental Corp.).
The new antenna modules work in combination with a full transceiver module. The transceiver can be mounted in the roof panels or the trunk deck near the antenna or separated by a distance as required by design and connected via cable (figure below, courtesy Delphi).
These transceivers are different from non-automotive models, as they support CAN, FlexRay and LIN in addition to Wi-Fi for the Ethernet management. The network support includes the standard VPN, security, firewall and router functions.
To date, the antenna systems in cars have been designed in as an "add on" to the primary vehicle design. With the increasing use of RF systems coming into play for in-car communication, and the current trend in adding features wirelessly to reduce weight by not adding wires, the number of frequencies and antennas is increasing. Soon, the antenna placement and signal distribution in the vehicle design will be one of the key design considerations, on par with the safety and aesthetic design aspects.