Rainbow Electronics RC2200 - Manual (Page 11)

RC220x
 2005 Radiocrafts AS RC220x Data Sheet (rev. 1.0) Page 11 of 17
Antenna and Range Considerations
As an option the module is delivered with an integrated antenna (RC220xAT). This is highly
recommended for most applications, as this gives a very compact solution containing all the
critical RF parts within the module.
Range testing using the integrated antenna shows these typical distances:
• 110 meter outdoor line-of-sight (LOS)
• 10-30 meters indoors depending on building material and construction
• 10-15 meters when passing through floors
• 25-30 meters in the same floor
The variation between different orientations of the antenna measured outdoors line-of-sight is
typically within +/- 20%.
The integrated antenna is a compact ceramic antenna working as a quarter-wave resonant
antenna. Due to the dielectric ceramic material the antenna is shorter than a normal quarter
wave antenna (in air), still providing high radiation efficiency (typical 1 dBi). The antenna is
matched for use in the 2.45 GHz band. The radiating part of the antenna is the white ceramic
component located outside the shield can. The radiation pattern from the antenna is similar to
the donut-shaped radiation from a quarter wave antenna. That is, the maximum radiation is in
the plane normal to the length axis of the antenna. For best possible omni-directional
radiation the module should be oriented so that the antenna is vertical. To achieve the very
best range the transmitting and receiving antenna should be oriented the same way, ensuring
the same polarity at both devices. However, indoors reflections of the radio waves in metallic
structures tend to spread the polarisation, so even if same orientation is not possible,
communication will still take place, but the range is somewhat shorter, typically by 20%.
The antenna should be kept away (> 10mm) from metallic or other conductive and dielectric
materials, and should never be used inside a metallic enclosure.
Compared to lower frequencies, operation at 2.45 GHz is more limited to LOS. Reflections
from walls and other objects may give multi-path fading resulting in dead-zones. The ZigBee
mesh network topology is used to overcome this fading as it allows for alternative routing
paths. The mesh network is therefore highly recommended for increased reliability and
extended coverage throughout buildings.
In applications where the module must be placed in a metallic enclosure, an external antenna
must be used. The MMCX connector option (RC220xMM) can then be used to launch a
coaxial cable connecting to the external antenna. It is not recommended to connect a whip
antenna directly to the MMCX connector as it does not support the mechanical strength
required for necessary robustness with such an antenna.
If the option without antenna or MCCX is chosen (RC220x), the RF output must be connected
to an antenna through the RF pin. The RF input/output is matched to 50 Ohm. If the antenna
or antenna connector is placed away from the module at the motherboard, the track between
the RF pin and the connector should be a 50 Ohm transmission line.
On a two layer board made of FR4 the width of a microstrip transmission line should be 1.8
times the thickness of the board, assuming a dielectric constant of 4.8. The line should be run
at the top of the board, and the bottom side should be a ground plane.
Example: For a 1.6 mm thick FR4 board, the width of the trace on the top side should be 1.8 x
1.6 mm = 2.88 mm.