In the ever-changing world of mobile
computing, fleet managers are faced with getting the right pieces to maximize
their wireless computing solutions. One of the critical pieces of that system
is the vehicular antenna. Surprisingly, it is one of those parts in the system
that often gets overlooked. In reality, the antenna is one of the most vital
pieces to the puzzle. An agency may spend huge money on the best laptop, best
mounting setup, and best software only to have the entire system weak because
they bought the wrong or cheap antenna.
Vehicle antennas started out as big,
tall “whips” used mostly for Land Mobile Radio. That was long before both
“voice” and “data” were both something we wanted from a vehicle with a computer
system. These whip antennas were susceptible to damage in car washes,
vandalism, undergrounds, bushes, or any type of external obstruction. They were
also designed strictly for a single frequency.
Along came GPS availability and the
demand for compact GPS antennas. The military’s GPS research and development also
carried over to the data side. As technology advanced, more demand was created
with mobile data terminals in vehicles and so did the demand for smaller
packaging, better construction, and multiple frequencies in a single housing.
The first multi antennas were cellular and GPS in a single housing. That became
the now-popular, low-profile “Hockey Puck” antenna.
The technology advanced, multiple
cellular frequencies and multiple data frequencies were combined in one unit.
First generations of these low-profile antennas combined 2G, 3G frequencies
usually in the 800 MHz to 2.4 GHz cellular range and included embedded GPS
transceivers all in one housing.
As law enforcement moved to computers in
vehicles, data connectivity became more important. Simple text transmissions
from older Mobile Data Terminals have given way to high-speed data transfer of text, photographs, mobile video, and other
large files. To push WiFi, 4G cellular and GPS through the same docking pass-through,
you need more options in your external antennas. The other option is to use a
USB connector coming from the same multi-purpose antenna.
For the most part, the major antenna
makers make a decent product. However, there are differences that fleet managers
need to know about. From an appearance standpoint, most police antennas look about
the same, but they are definitely not. Fleet managers need to determine which mobile
technologies they need the antenna to transmit. Then the manufacturer can
combine these technologies in one housing for simple installation, be they wireless
PC cards (AirCard), rugged trunk modems, embedded wireless in rugged laptops,
or wireless mobile access routers (MARs).
Don’t get caught with legacy technology!
Fleet managers must make sure to future-proof their agency against the constant
technology changes by the cellular carriers. Just because your area of
responsibility might still be 3G doesn’t mean you buy a single-purpose 3G
antenna. Always purchase the combo antennas that have both 3G and 4G
technologies built in. The life span of fleet vehicles can be years and within
those years, cellular data technology will advance at a much faster rate.
It is common place to have antennas with
multiple voice, data and GPS frequencies all in a single housing. There are
three basic types of antennas: omni-directional, semi-directional and highly directional.
For mobile data transfer in a moving vehicle, omni-directional, low-profile
antennas are clearly the most preferred.
The best ground plane location on a
moving vehicle is the roof, period. The trunk “can” be used, but it is definitely
not the best location. Being mounted higher on the vehicle will allow for less
possibility of obstruction or reflection. In policing, lightbars do play a role
in how the rooftop is laid out on your vehicles. The standard rule is to place
the antennas 15-20 inches to the rear of the lightbar and to separate the voice
and data antennas equally to each side of the roof.
In the early days, some agencies would
have wireless cellular data transfer through AirCards inserted into their
vehicle laptops. The AirCards came with a small 3-inch antenna that stuck out
the side of the laptop. Most of the time it worked fine. However, the
environment inside of a police vehicle is “RF tight.” The coated, sound-deadened
auto glass, metal siding, and insulation all act to shield both radio and
cellular data transfer rates.
If that vehicle is in an urban
environment with lots of cell towers around and high signal strength, it’s
probably all right. But if that same vehicle is moving from urban to rural,
then connectivity will be significantly reduced. Moving the antenna to the
outside of a vehicle will improve signal strength 5-10 dB, and that is
When buying police vehicle antennas, the
quality of the design and manufacturing must always take precedence over price.
This is more important than in what country the antenna is built. There many subtle
differences in quality that greatly affect communications. Consider antenna
body materials. Manufacturers like Antenna Plus use glass-filled polypropolene
for all antenna housings. This prevents UV fade or cracking even in extremely
sunny areas. With a cheaper antenna made from polycarbonate, you may end up
with a yellow antenna on the roof of your white police unit.
The best advice is to educate yourself
on the technologies in your area of responsibility. Talk to your IT people and
cellular company technicians. Determine what is coming down the road. The
latest antenna technology is called MIMO, which stands for Multiple-Input,
Multiple-Output. With a MIMO antenna
configuration, you can realize the fastest speeds LTE offers, as the antennas
are working simultaneously on both the uplink and downlink. Engineers
determined that if you add another antenna, you can significantly increase the
While the newer protocols
are the bigger reason speeds have increased, these new antennas enable the peak
speeds, and are an important part of the whole setup. In the mobile environment,
it is now possible to encroach on data transfer speeds that were once reserved
for hardline cable networks. This allows anytime, anywhere data transfer for
things like video, mugshots, software updates once reserved for updating only
when the vehicles were within range of private or public WiFi.
Antennas & Bandwidth
Since the beginning of radio technology,
we have become accustomed to a mobile phone, wireless laptop, or Land Mobile
Radio transmitting with a single antenna. This transmission travels through the
air and is received by a much larger antenna on a cellular provider’s tower, which
in turn rebroadcasts the signal to your intended destination. For transmitting
a phone call, this technology is simple and effective. As wireless technology
itself continues its increasing demand for faster and more reliable 3G/4G
wireless data transfer, more complex methods of transmitting were needed.
Most agencies have been using 3G
wireless data for a few years now but the top speeds have been rapidly
increasing, starting around 3.6 Mbps for the first series of mobile broadband
modems, to 7.2 Mbps around 2007, to 21 Mbps in 2008, to 42 Mbps shortly after,
and now 100 Mbps with the 4G LTE introduction in late 2011.
In the theoretical world, the biggest
factor in limiting speed is bandwidth. Each phone tower has a given total width
of frequencies on which it can transmit, with each person who connects being
allocated a small channel of a certain width. This means that each tower has a
limited number of vehicles it can service before becoming congested, especially
in densely populated urban areas.
As engineers max out the performance,
they can from single antenna to single antenna transmission, but they had to
approach the problem differently. This is where MIMO comes in to play. Since
they cannot improve single antenna air transmission any further, why not
increase the number of antennas?
MIMO technology has gained attention in
wireless communications because it offers significant increases in data
throughput and link range without additional bandwidth or increased transmit
power. It achieves this goal by spreading the same total transmit power over
the antennas to achieve a gain that improves the spectral efficiency as well
improves the link reliability (reduced signal loss or fading). Because of these
properties, MIMO is an important part of modern wireless communication
standards such as 802.11 (Wi-Fi), 4GLTE, WiMax and HSPA+.
Many of the latest
rugged trunk-based modems and mobile access routers now come standard with two
cellular/LTE antenna ports, a WiFi port (sometimes two), as well as GPS. Antenna
manufacturers have also started to come out with antennas that build all of
this into one low-profile housing.
Antenna Plus has
recently come out with the cutting-edge AP-Mobile-Access-Router-MIMO Antenna,
which provides the two MIMO Cellular/LTE antennas, two MIMO WiFi, and a GPS
antenna all in one low-profile housing. When you consider that in making just
the cellular/LTE antenna part, they have to build in frequency ranges for
800/1900 MHz for 3G and then 700/1700/2100 MHz for LTE, it is really amazing
that they can do all this in such a small housing. When you are making your
antenna choice, it makes sense to go with those who have been in the business
for a long time and have demonstrated a commitment to public safety, building
in the highest technical standards.
Antenna support is also important;
however, 90 percent of all issues or failures in antenna troubleshooting
usually end up being the connectors at the end of the coax. Typically, the
center conductor gets disconnected from the connector due to poor installation
or no strain relief.
Upfit tip: buy the connectors attached
by the antenna manufacturer or make sure they are installed with care and
connected properly. Equipment downtime is a killer in any profession and even
more critical if the front line officer can’t get instant access to mission-critical
information to make decisions that often escalate to life-and-death decisions.
At that point, it won’t matter what you paid for the antenna, only that you
bought the right one for your application.
Brewer is a 23-year member of the Vancouver Police Department. He sits on the
Ford Police Advisory Board and regularly gives presentations at law enforcement
conferences on mobile computing, wireless technology and police vehicle
ergonomics. He can be reached at firstname.lastname@example.org.