User's Manual

microNode Integration Specification Antenna Diversity
On-Ramp Wireless, Inc. 39 014-0033-00 Rev. H
8.1 Antenna Design Considerations
Good antenna design is also crucial to success. It is important to consider some pertinent issues.
 Ceramic antennas can work well but may sometimes have issues. Careful testing must be
done to ensure desired gains and radiation patterns.
 The product must be researched in conjunction to the Access Point, its deployment, and its
antenna radiation pattern. Nominally the Access Point will be mounted on a tower or
mountain with a downward tilt. The microNode and System may be mounted vertically or
horizontally—forcing requirements on the optimal radiation pattern of the microNode.
 The antenna must be well matched and with low loss between microNode and antenna. It is
important to follow the manufacturer’s recommendations. The use of low tolerance ceramic
capacitors and low tolerance thin film inductors are recommended. Examples include the
Murata GJM series of capacitors and LQP series of inductors. If using stripline RF port feeds,
care must be employed to ensure low loss and proper impedance. The antenna match may
change when fully integrated into a product. Is advised to recheck the match after full
integration. During tuning this may require the use of so called “RF pigtails” in an ad hoc
fashion. If the Bill of Materials (BOM) cost will allow, a special connector can be
implemented to support this verification/optimization.
 Metallic objects nearby to the antenna can affect radiation gains, patterns, and power
match. Typically anything within about 4-5 inches can affect the match significantly
particularly if the nearby metal is resonant at 2.4 GHz. A little pattern distortion usually is
not of too much concern unless deep wide angular nulls in the antenna pattern results.
Other types of pattern distortion can be caused by absorptive losses due to lossy dielectrics
nearby the antenna, which represents real power loss dissipated as heat in the loss object.
This represents power that is completely lost and not radiated in a useful direction.
 Noisy System clocks with harmonics can fall into the operating band of the microNode and
can be picked up by the antennas—degrading sensitivity, or causing Electromagnetic
Compatibility (EMC) regulatory failures.
8.2 Diversity Considerations
The operating frequency of the microNode is the ISM 2.4GHz band. This has a wavelength of
12.3 cm in air. For optimal null/peak diversity detection, the antennas must be separated by at
least 2.5” (5cm). It is a good idea on the diversity antenna to orient it 90 degrees from the main
antenna in order to improve on polarization diversity between antennas in addition to spatial
de-correlation.
Practical ground plane-independent antennas are preferable to those that require the printed
circuit board (PCB) copper for the antenna counterpoise. Examples of these are dipole antennas
and some chip patch antennas. However these can be cost adders in certain cases. It should be
noted however that some chip antennas that use the PCB for ground return have been shown to
produce reasonable performance.