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.