Smart Transportation Management Systems – Lessons from the 2017 ITS World Congress
Once again Mobile Mark Antenna Solutions exhibited at the ITS World Congress. This year it was held in Montreal, Canada from Oct 30 – Nov 2, 2017.
It is always exciting to see the developments that have taken place during the year, and for us it is especially exciting to connect with our partners and learn more about the trials they have participated in and the experiences they have had with Mobile Mark antennas. Several of the exhibitors were displaying our omni-directional antennas as part of their RSUs (Roadside Units).
One of the messages coming out of this year’s congress is that smart transportation management systems need efficient, well-designed car antennas to ensure reliable wireless connection. Mobile Mark’s new multi-band V2V antenna for MIMO DSRC and combined GPS/Glonass was on display in our booth. This new antenna is designed to minimize DSRC shadowing which will result in more consistent and more balanced coverage.
Factors to Consider When Choosing Antennas for Smart Transportation Management Systems
DSRC shadowing is one factor that can be used in evaluating antennas for trials of connected-cars and autonomous-cars. We recommend these other essential “Need to Know” factors when selecting antennas for optimal V2V coverage in a Smart Transportation Management System.
- Use multiple criteria when evaluating antennas to feel confident in the selection.
- Review accurate antenna radiation patterns acquired with ALL internal elements present. Make sure the pattern is as close to round as possible; antennas with nulls greater than 3 dB should be avoided.
- Review the geographic terrain and the mix of vehicles when evaluating antenna gain; higher gain is not necessarily better.
- Review the vehicle for any inherent obstacles that that can cause pattern interference; items such as additional antennas, roof racks or trim items can cause shadowing of the patterns.
The importance of these factors was developed in more detail in an article that appeared in the Aug/Sep 2017 issue of Traffic Technology International. A copy appears below:
How Shadowing Can Diminish V2V Coverage
Published in Traffic Technology International, Aug/Sep 2017
Reliable V2V communications is critical to an effective Intelligent Transportation System, and selecting reliable antennas is key to achieving that goal. Parameters such as gain, beamwidth and efficiency are important. In this article, we will also address “shadowing,” a challenge that arises when multiple antenna elements are combined in the same antenna housing.
Wireless systems involved in Vehicle Telematics have become increasingly complex. A simple DSRC network at 5.9 GHz may now be used in conjunction with Cellular, WiFi, GPS or Glonass. Some trials may require multiple streams for MIMO (multiple-input-multiple-output) coverage.
As the number of systems increase, there is a growing desire to combine some of these antennas into a consolidated package. Effective design work can ensure optimum performance for each antenna element and minimize interaction among the elements. The only way to truly gauge the shadowing effects is to carefully study the antenna’s azimuth pattern which should show a near round pattern without any nulls greater than 3 dB.
Higher gain antennas can transmit signals over longer distances, but V2V communications will take place in close distances with the most critical communications exchanged within 100 meters. Lower gain antennas have a broader hemispherical coverage than higher gain antennas which exhibit wider but flatter coverage. For communications in hilly terrain or among vehicles of drastically different heights, such as between a Bus and a Ferrari, the hemispherical coverage will be more effective.
Shadowing can be created by the environment in which the antenna is mounted or it can be created by the antenna itself. For example, we would expect that antennas mounted on the trunk of a vehicle will find their forward-facing signals are blocked by the car itself, but we will also find that the metal around the installation setting will skew their radiation pattern facing out and back. For this reason, many DSRC antennas will be best positioned on the roof of the vehicle, where there is better line-of-sight for the RF signal.
Shadowing can also occur from the way the antenna itself is designed. The positioning of the antenna elements within the antenna can create undesirable trade-offs. Some elements may “block” or “redirect” the signal of a neighboring element, creating an uneven radiation pattern.
It isn’t necessary to break the antenna open to check for the possibility of shadowing. It can be detected by looking at the radiation pattern. Testing the antenna on a standard ground plane, measured in free space will allow us to evaluate the antenna itself, independent of any impact from the vehicle setting. Nulls in the omni-directional radiation pattern are an indication that some degree of shadowing is occurring within the antenna itself. Non-circular patterns with nulls greater than 3 dB will drastically reduce V2V dependability.
Shadowing can occur when antenna elements are positioned on different physical planes within the antenna and can often be eliminated by redesigning the board positions with the express desire of reducing or eliminating the shadowing affect. Critical antenna elements that are essential for collision avoidance and other safety-oriented communications, in this case the DSRC elements, should be located so that they are not shadowed by other antenna elements. When ideally designed and positioned, the radiation pattern of these elements should be balanced and even in the horizontal plane. Any nulls in the radiation pattern should not exceed 3 dB variation throughout the omni pattern.
Antenna gain and VSWR performance are two important measures for evaluating antennas. Checking for the impact of shadowing on the radiation pattern is another important guide for selecting the right antenna.
(This article, which covers the importance of antenna design in a smart transportation management systems, appeared in the Aug/Sep 2017 issue of Traffic Technology International.)