Technologies' telemetry and communications products operate in
the cellular telephone band (835 MHz-880 MHz). Virtual
Technologies offers a wide variety of antennas for these
applications. All antennas that we offer can be classified
into the following basic groups.
antenna type is detailed below. Each of the sections
discusses the attributes, strengths and weaknesses of each
antenna type. Along with information about specific
antennas, keep the following points in mind as you choose an
are distorted by nearby objects (particularly metal ones).
Avoid placing the antenna near a distorting object, to
insure proper performance.
Because cell site
antennas are vertically polarized, antennas that are mounted
vertically will perform better than ones that are mounted
Keep the antenna
as far away as practical from sensitive circuitry such as
A/D converters, clock signal traces, and other noise
generators. Otherwise you may find that the signals couple
onto the antenna coaxial cable or CRFM board. If this
happens, these signals will
be radiated by the antenna and
be conducted into the receiver, making it less sensitive to the
desired control channel signals.
Use of connectors
and interconnecting cable should be minimized. Each of
these items has some RF loss associated with it. For cable
runs longer than 5 feet, we recommend Belden RF cable type
9913 or better. Loss in the transmit chain allows less
of the transmitter's power to get to the antenna to be
radiated. Loss in the receive chain causes less of the
received power to get from the antenna to the receiver
circuitry for decoding. In fringe areas these
additional tenths of dB may mean the difference between
working and not working.
Do not paint the
hole through which your antenna connects. Paint near the
antenna hole or antenna connector hole will prevent good
contact between the connector and the grounded case.
quarter wave antenna has an omnidirectional pattern; it radiates
equally well in all directions. This type of radiation
pattern is preferred in mobile applications as the bearing from
the device to the cellular tower is unknown or randomly
changing. The quarter-wave antenna may also be used in
fixed applications having a good ground plane and adequate
different types of antennas, the quarter-wave has the least
amount of gain. The quarter-wave does nothing to boost the
received signal and should be used where the signal strength is
quarter-wave requires a ground plane to work properly. A
ground plane is a flat surface designed to limit the downward
radiation of the antenna. Generally a large grounded piece of
metal is used. The ground plane should extend a minimum of one
wavelength (but preferably more) in each direction from the
antenna location. The wavelength at 850 MHz is over twelve
quarter-wave antenna is used without a sufficient ground plane,
two things will happen:
power will tend to go out equally in all directions. Up and
down as well as towards the horizon. Because there are no radio towers up and down, energy is
wasted which would be better used transmitting toward the towers.
improperly installed quarter-wave antenna does not establish
a good reference plane for the radiating field. When this
happens, the antenna is said to be mismatched
and the transmitter will see a high SWR (Standing Wave
Ratio). Much of the power that the transmitter
generates will then bounce back into the transmitter and be dissipated as
heat. This reduces
the signal that the cellular tower receives and may cause
improper decoding in fringe areas, along with spurious
half-wave antenna is omnidirectional and is well suited to both
fixed and mobile applications. It usually provides the
same gain as the quarter-wave, and can be used in installations
that won't support use of a quarter-wave antenna (i.e. an
installation without a ground plane). Though it has
similar gain properties to a quarter-wave, but it does not
require a large metal ground plane.
operates without a ground plane, the half-wave antenna's impact
on installation is minimal, but it is taller (more than twice
as tall, exceeding 9") than a quarter-wave antenna cut for the
same frequency. As the antenna is omnidirectional, device
placement during installation is straightforward.
antenna with gain becomes increasingly
bi-directional as gain increases.
It is best suited to fixed applications. It can provide
much more gain (typically +7dB) than the quarter-wave, and can
be used in installations that won't support use of a
quarter-wave antenna. Like the 0db half wave, it does not
require a large metal ground plane.
half-wave antenna is slightly more costly than the quarter-wave
but, the elimination of the quarter-wave's large ground plane
offsets this cost.
Half-Wave Radiation Pattern
co-linear antenna is omnidirectional and is well suited to fixed
and mobile applications. It provides higher gain than either the
0dB half-wave or the quarter-wave, and can be used in areas that
won't support the use of either of those antennas.
It does this by stacking half-wave
antennas on top of one another. Depending on how many half-wave
sections are internally combined, additional gain can be
realized. Typical gains are on the order of 3.0 - 4.5 dB. This
is equivalent to increasing the transmitter power from its
nominal 3 Watts to 6 or up to as much as 8.5 Watts (equivalent
power radiated by a quarter-wave). This radiated energy is
concentrated in an omnidirectional pattern, along the horizontal
plane, and is more focused towards the horizon.
type of antenna would most likely be installed in a far fringe
area, where no clear indication of the nearest cell site
direction was available, or in a fringe mobile application.
Co-Linear Radiation Pattern
- Ideal for Fixed Remote Sites
Yagi is a highly directional antenna consisting of an array of
single-wire dipole antennas and a series of reflectors. It looks
much like a UHF television antenna (though the pegs or pins are
oriented vertically instead of horizontally).
It must be aimed
at a cellular site, and for this reason it is only appropriate
for fixed installations. Of the four types of antennas discussed
above, the Yagi has the highest gain (+11dB or greater). It is the ideal antenna
for fixed installation in very remote areas where the direction
of the nearest cell tower is known.
Its proper installation requires
the use of a signal strength indicator (available on all Virtual
Technologies Virtu-Well and Water Watcher products).
External measurement equipment may also be used. The installer
must aim the antenna at the
time of installation. If a new cell site is installed by the
cellular carrier, the installer may have to revisit the site
to reorient the antenna to take advantage of the stronger,
A patch antenna is generally flat
or has very little thickness. It has a directional
characteristic and tends to radiate (or receive) best in the
direction normal to the large flat surface. You might
choose a patch when you want to hide the antenna. Depending on the size, they can have a varying amount of gain,
from about the same as a dipole to as much or more than a Yagi.
Because of their directional nature, they are most
effective in a fixed installation, though a low-gain patch
pointed up may suffice in very strong signal areas.
Unlike the whip type antennas mentioned above, it has an
inherent built-in Radome that protects it from
curious fingers. The following is a photograph of a patch