Sierra Wireless AIRPRIME WISMO218 - Manual (Page 77)

WA_DEV_W218_PTS_002 Rev 006 April 29, 2010 77
Product Technical Specification &
Customer Design Guidelines Interfaces
Characteristic AirPrime WISMO218
Impedance 50 
VSWR
Rx max 1.5 :1
Tx max 1.5 :1
Typical radiated gain 0dBi in one direction at least
Caution: Sierra Wireless strongly recommends working with an antenna manufacturer either to develop an
antenna adapted to the application or to adapt an existing solution to the application. Both the
mechanical and electrical antenna adaptations are one of the key issues in the design of the GSM
terminal.
The RF antenna connection uses one of the castellation pins of the AirPrime WISMO218, with
grounded castellation pins at both sides.
This castellation pin must be connected to an RF 50  line, in order to protect the antenna line from
the noise coming from base-band signals.
Figure 41. Example of an RF 50  line
This 50  line is surrounded by two ground planes in order to protect this antenna line from noise.
The length of the line shouldn’t be too long (more than a few centimeters) because of RF insertion
loss. The width of the line must be calculated in order to ensure a 50
 characteristic impedance.
For this same reason, the RF embedded line should likewise be kept about 1cm away from any
(noisy) baseband signal in order to ensure a good RX sensitivity level.
The other end of the RF 50  line can be connected to an RF connector or a soldering pad in order to
connect an antenna.
It is also possible to use an antenna chip or to design a PCB antenna directly on the application
board.
The ANT pin of the AirPrime WISMO218 is ESD protected, for both ±4KV contact and ±8KV air
discharge.
Castellation pin for ANT
50  RF line