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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

Figure 40Figure 40

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.)

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