SARA-G3 series - System Integration Manual
UBX-13000995 - R06
Objective Specification
Design-in
Page 112 of 218
2.3
Antenna interface
The
ANT
pin, provided by all SARA-G3 modules, represents the main RF input/output used to transmit
and receive the GSM/GPRS RF signal: the main antenna must be connected to this pad. The
ANT
pin
has a nominal characteristic impedance of 50
and must be connected to the antenna through a 50
transmission line to allow transmission and reception of radio frequency (RF) signals in the 2G and 3G
operating bands.
2.3.1
Antenna RF interface (ANT)
2.3.1.1
General guidelines for antenna selection and design
The GSM antenna is the most critical component to be evaluated: care must be taken about it at the
start of the design development, when the physical dimensions of the application board are under
analysis/decision, since the RF compliance of the device integrating SARA-G3 module with all the
applicable required certification schemes depends from antenna radiating performance.
GSM antennas are typically available as:
Linear monopole / External antenna:
o
External antenna usage basically does not imply physical restriction to the design of the PCB
where the SARA-G3 series module is mounted
o
The radiation performance mainly depends on the antenna: select the antenna with optimal
radiating performance in the operating bands
o
If antenna detection functionality is required, select an antenna assembly provided with a
proper built-in diagnostic circuit with a resistor connected to ground: refer to guidelines in
section
o
Select an RF cable with minimum insertion loss: additional insertion loss due to low quality or
long cable reduces radiation performance
o
Select a suitable 50
connector providing proper PCB-to-RF-cable transition: it is
recommended to strictly follow the layout guidelines provided by the connector manufacturer
Patch-like antenna / Integrated antenna:
o
Internal integrated antenna implies physical restriction to the design of the PCB: the ground
plane can be reduced down to a minimum size that must be similar to the quarter of the
wavelength of the minimum frequency that has to be radiated. As numerical example:
Frequency = 1 GHz
Wavelength = 30 cm
Minimum GND plane size = 7.5 cm
o
The radiation performance depends on the whole PCB and antenna system design, including
product mechanical design and usage: select the antenna with optimal radiating performance in
the operating bands according to the mechanical specifications of the PCB and the whole
product
o
Select a complete custom antenna designed by an antenna manufacturer if the required ground
plane dimensions are very small (e.g. less than 6.5 cm long and 4 cm wide): the antenna
design process should begin at the start of the whole product design process
Formatted:
English (U.S.)
