SARA-G3 series - System Integration Manual
UBX-13000995 - R06
Objective Specification
Design-in
Page 117 of 218
If an external antenna is used, the antenna connector represents the RF termination on the PCB:
Use a suitable 50
connector providing proper PCB-to-RF-cable transition
Strictly follow the connector manufacturer’s recommended layout, for example:
o
SMA Pin-Through-Hole connectors require GND keep-out (i.e. clearance, a void area) on
all the layers around the central pin up to annular pads of the four GND posts, as shown in
o
U.FL surface mounted connectors require no conductive traces (i.e. clearance, a void area)
in the area below the connector between the GND land pads
Cut out the GND layer under RF connectors and close to buried vias, to remove stray capacitance
and thus keep the RF line 50
: e.g. the active pad of U.FL connectors needs to have a GND
keep-out (i.e. clearance, a void area) at least on first inner layer to reduce parasitic capacitance to
ground
If an integrated antenna is used, the RF termination is represented by the integrated antenna itself:
Use an antenna designed by an antenna manufacturer, providing the best possible return loss (or
V.S.W.R.)
Provide a ground plane large enough according to the related integrated antenna requirements: the
ground plane of the application PCB can be reduced to a minimum size that must be similar to one
quarter of 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
It is highly recommended to strictly follow the detailed and specific guidelines provided by the antenna
manufacturer regarding correct installation and deployment of the antenna system, including PCB layout
and matching circuitry
Further to the custom PCB and product restrictions, the antenna may require a tuning to comply with
all the applicable required certification schemes. It is recommended to consult the antenna manufacturer
for the design-in guidelines for the antenna related to the custom application
Additionally, these recommendations regarding the antenna system must be followed:
Do not include antenna within closed metal case
Do not place the antenna in close vicinity to end users, since the emitted radiation in human tissue is
limited by regulatory requirements
Place the antenna far from sensitive analog systems or employ countermeasures to reduce
electromagnetic compatibility issues
Take care of interaction between co-located RF systems since the GSM transmitted power may interact
or disturb the performance of companion systems
The antenna shall provide optimal efficiency figure over all the operating frequencies
The antenna shall provide appropriate gain figure (i.e. combined antenna directivity and efficiency
figure) so that the electromagnetic field radiation intensity does not exceed the regulatory limits
specified in some countries (e.g. by FCC in the United States, as reported in section 4.2.2)
Formatted:
English (U.S.)
Formatted:
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