RIM 1802G, Integrator Manual

Page: 63 / 76

Antenna design considerations
Integrator Guide 63
Vertical polarization
Because the GPRS network is based on a vertically polarized radio-frequency transmission, the
application’s antenna should be oriented vertically and upward when the radio modem is in use. In
small, handheld devices, a user-friendly design enables the antenna to be folded out of the way
when it is not in use.
Proximity to active electronics
You should position the antenna as far from the computing device’s active electronics as possible.
Metal construction in a computing device’s case and internal components may attenuate the signal
in certain directions, which reduces the radio modem’s sensitivity and transmit performance when
the computing device is held or oriented in certain ways. Using metal in the construction of a
ground plane for an antenna can significantly improve the antenna gain and the system’s coverage.
Transmission interference
To prevent interference from the antenna into the radio modem during transmission, the antenna
must be placed a minimum of 2 cm (0.8”) away from the radio modem. For best performance, the
antenna should be placed more than 5 cm (2”) away from the radio modem.
Device position
If the computing device is designed to sit on a surface, the antenna should be as far from the bottom
of the device as possible. This reduces radio frequency (RF) reflections when the device is placed on
a metal surface.
When the computing device is handheld or is worn next to the user’s body, the antenna should be
positioned to radiate away from the body. Otherwise, the body absorbs the radiated energy and the
effective coverage area of the radio is reduced. Positioning the antenna away from the body also
helps the device meet the FCC RF exposure (SAR/MPE) requirements.
Antenna cable
For best results, the antenna should be connected directly to the antenna cable. If you require an
extension cable, it should be low loss, as short as possible, and have an impedance of 50 ohms. You
must use a proper matching connector, because each connector in the signal path introduces a
return loss and reduces performance.