Integration Manual
SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R13 Design-in Page 61 of 119
• In the second example shown on the right, the ANT pin is connected to an SMA connector by means of a suitable
50 Ω transmission line, designed with the appropriate layout, with an additional high pass filter to improve the ESD
immunity at the antenna port. (The filter consists of a suitable series capacitor and shunt inductor, for example the
Murata GRM1555C1H150JA01 15 pF capacitor and the Murata LQG15HN39NJ02 39 nH inductor with Self-Resonant
Frequency ~1 GHz.).
SARA m odule
SM A
connect or
SA RA m odule
SM A
connect or
High -pass filt er
t o im prove
ESD im m unit y
Figure 34: Example of circuit and layout for antenna RF circuits on the application board
Guidelines for RF termination design
The RF termination must provide a characteristic impedance of 50 Ω as well as the RF transmission line up to the RF
termination, to match the characteristic impedance of the ANT port.
However, real antennas do not have a perfect 50 Ω load on all the supported frequency bands. So to reduce as much as
possible any performance degradation due to antenna mismatching, the RF termination must provide optimal return loss
(or VSWR) figures over all the operating frequencies, as summarized in Table 7.
If an external antenna is used, the antenna connector represents the RF termination on the PCB:
• Use suitable a 50 Ω connector providing a clean PCB-to-RF-cable transition.
• Strictly follow the connector manufacturer’s recommended layout, for example:
o SMA Pin-Through-Hole connectors require a GND keep-out (i.e. clearance, a void area) on all the layers around
the central pin up to the annular pads of the four GND posts, as shown in Figure 34
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 the RF connector and close to any buried vias, to remove stray capacitance and thus
keep the RF line at 50 Ω, e.g. the active pad of UFL connector needs to have a GND keep-out (i.e. clearance, a void
area) at least on the first inner layer to reduce parasitic capacitance to ground.
If an integrated antenna is used, the integrated antenna represents the RF terminations. The following guidelines should
be followed:
• Use an antenna designed by an antenna manufacturer providing the best possible return loss (or VSWR).
• Provide a ground plane large enough according to the relative integrated antenna requirements. The ground plane
of the application PCB can be reduced down to a minimum size that must be similar to one quarter of wavelength of
the minimum frequency that needs to be radiated. As numerical example,
Frequency = 750 MHz Wavelength = 40 cm Minimum GND plane size = 10 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 the 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 matching relative to the custom application.