ANTENNAS
18
Dragonfly
TM
MTQ-LEU7 Device Guide
Antenna Diversity
Antenna diversity uses two receive antennas to improve the downlink connection (cell tower to mobile). It has no
effect on the uplink (mobile to cell tower).
Antenna diversity is useful in environments where the signal arrives at the device after bouncing off or around
buildings or other objects. The bounced signal may be attenuated by going through semi-transparent (to the
signal) objects. Each signal alteration can change its magnitude, phase, orientation, or polarization. This complex
environment can exist in cities, inside buildings or in traffic. In this environment, signal paths from the cell tower
form an interference pattern of peaks and nulls. These peaks and nulls can be very close together.
Antenna diversity provides an advantage in complex environments because if one receive antenna has a poor
signal due to an interference null pattern, the other antenna is likely not in the null and has better reception. The
radio compares the reception from both receive antennas and uses the one with the strongest signal.
Antenna diversity is unnecessary when the device has an unobstructed signal path from the cell tower, such as in a
flat area away from buildings. In good reception environments, the product application might prohibit using two
receive antennas.
Using Antenna Diversity
You can use an AT command to turn antenna diversity on and off. When antenna diversity is on and a like or
similar antenna is installed on both radio connectors, the radio automatically chooses the antenna with the best
reception. To learn about the AT command used to control diversity, see the AT Command Reference guide for
your device.
Placing External Antennas
Antennas are usually a quarter wavelength apart from each other. With multiband radios where the quarter
wavelengths in each band are diverse from each other, this rule may not be practical. Choose spacing based on the
band used most often or the band with connection difficulty. Some environments are harsher on particular bands.
Multi-Tech products have antenna connectors at the best spacing for the product size.
Placing antennas in close proximity to each other is not optimal, but you can do it if necessary. It depends on the
signal strength to and from each antenna.
Selecting Antennas
Select an antenna based on your product and application. Typically, both antennas are the same because either
can be the main receive antenna. However, if the antenna connectors are too close together, use a similar antenna
on a short cable for the second receive only antenna.
Antenna Approvals and Safety Considerations
Note the following:
The carriers conduct antenna diversity tests.
There are no EMC concerns about antenna diversity.
All antennas need to have a minimum flammability rating.
Safety requirements depend on your final product.
Antennas are not approved for outdoor use. Do not extend antennas outside of any building.
