Integration Manual

SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R11 Design-in Page 80 of 157
o It is recommended to select a custom antenna designed by an antennas’ 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
o 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
o Further to the custom PCB and product restrictions, antennas may require tuning to obtain the
required performance for compliance with all the applicable required certification schemes. It is
recommended to consult the antenna manufacturer for the design-in guidelines for antenna
matching relative to the custom application
In both of cases, selecting external or internal antennas, these recommendations should be observed:
 Select an antenna providing optimal return loss (or VSWR) figure over all the operating frequencies.
 Select an antenna providing optimal efficiency figure over all the operating frequencies.
 Select an antenna providing appropriate gain figure (i.e. combined antenna directivity and efficiency
figure) so that the electromagnetic field radiation intensity do not exceed the regulatory limits specified
in some countries (e.g. by FCC in the United States, as reported in the section 4.2.2).
2.4.1.2 Guidelines for antenna RF interface design
Guidelines for ANT pin RF connection design
A clean transition between the ANT pad and the application board PCB must be provided, implementing
the following design-in guidelines for the layout of the application PCB close to the ANT pad:
 On a multilayer board, the whole layer stack below the RF connection should be free of digital lines
 Increase GND keep-out (i.e. clearance, a void area) around the ANT pad, on the top layer of the
application PCB, to at least 250 µm up to adjacent pads metal definition and up to 400 µm on the area
below the module, to reduce parasitic capacitance to ground, as described in the left picture in Figure
31
 Add GND keep-out (i.e. clearance, a void area) on the buried metal layer below the ANT pad if the top-
layer to buried layer dielectric thickness is below 200 µm, to reduce parasitic capacitance to ground, as
described in the right picture in Figure 31