u-blox LARA-R2 series System Integration Manual page 86

Radiation performance depends on the whole PCB and antenna system design, including product
o
mechanical design and usage. Antennas should be selected with optimal radiating performance in the
operating bands according to the mechanical specifications of the PCB and the whole product.
It is recommended to select a pair of custom antennas designed by an antennas' manufacturer if the
o
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
It is highly recommended to strictly follow the detailed and specific guidelines provided by the antenna
o
manufacturer regarding correct installation and deployment of the antenna system, including PCB layout
and matching circuitry
Further to the custom PCB and product restrictions, antennas may require tuning to obtain the required
o
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 antennas providing optimal return loss (or V.S.W.R.) figure over all the operating frequencies.

Select antennas providing optimal efficiency figure over all the operating frequencies.

Select antennas providing similar efficiency for both the primary (ANT1) and the secondary (ANT2) antenna.

Select antennas 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).

Select antennas capable to provide low Envelope Correlation Coefficient between the primary (ANT1) and
the secondary (ANT2) antenna: the 3D antenna radiation patterns should have lobes in different directions.
2.4.1.2 Guidelines for antenna RF interface design
Guidelines for ANT1 / ANT2 pins RF connection design
Proper transition between ANT1 / ANT2 pads and the application board PCB must be provided, implementing
the following design-in guidelines for the layout of the application PCB close to the ANT1 / ANT2 pads:

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 ANT1 / ANT2 pads, 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 39

Add GND keep-out (i.e. clearance, a void area) on the buried metal layer below the ANT1 / ANT2 pads 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 39
GND clearance
on top layer
around ANT1 pad
250 µm
ANT1
Min. 400 µm
Figure 39: GND keep-out area on top layer around ANT1 / ANT2 pads and on very close buried layer below ANT1 / ANT2 pads
UBX-16010573 - R02
GND clearance
on very close buried layer
below ANT1 pad
Min.
GND
LARA-R2 series - System Integration Manual
GND clearance
on top layer
around ANT2 pad
ANT2
Objective Specification
on very close buried layer
below ANT2 pad
Min.
250 µm
GND
Min. 400 µm
GND clearance
Design-in
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