SARA-R4 series - System integration manual
UBX-16029218 - R20
Design-in
Page 61 of 128
C1-Public
2.4
Antenna interfaces
SARA-R4 series modules provide an RF interface for connecting the external antenna: the
ANT
pin
represents the RF input/output for RF signals transmission and reception.
SARA-R422M8S modules provide also a GNSS RF interface for connecting the external GNSS
antenna: the
ANT_GNSS
pin represents the GNSS RF input for GNSS signals reception.
The
ANT
and
ANT_GNSS
pins have a nominal characteristic impedance of 50
and must be
connected to the related external antenna system through a 50
transmission line to allow clean
transmission / reception of RF signals.
2.4.1
General guidelines for antenna interfaces
2.4.1.1
Guidelines for ANT and ANT_GNSS pins RF connection design
☞
The GNSS antenna RF interface is supported by SARA-R422M8S modules only.
A clean transition between the
ANT
and
ANT_GNSS
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
ANT
and
ANT_GNSS
pads:
•
On a multilayer board, the whole layer stack below the RF connections should be free of digital lines
•
Increase GND keep-out (i.e. clearance, a void area) around the
ANT
and
ANT_GNSS
pads, on the
top layer of the application PCB, to at least 250
m up to adjacent pads metal definition and up to
400
m on the area below the module, to reduce parasitic capacitance to ground, as described in
the left picture in
•
Add GND keep-out (i.e. clearance, a void area) on the buried metal layer below the
ANT
and
ANT_GNSS
pads if the top-layer to buried layer dielectric thickness is below 200
m, to reduce
parasitic capacitance to ground, as described in the right picture in
Min.
250
µ
m
Min. 400
µ
m
GND
RF pad
GND clearance
on buried layer very close to top layer
below RF pad
GND clearance
on top layer
around RF pad
Figure 35: GND keep-out area on top layer around RF pad and on very close buried layer below RF pad (ANT / ANT_GNSS)
