SARA-R4 series - System integration manual
UBX-16029218 - R20
Design-in
Page 65 of 128
C1-Public
•
Place the antenna far from sensitive analog systems or employ countermeasures to reduce EMC
or EMI issues.
•
Be aware of interaction between co-located RF systems since the LTE transmitted power may
interact or affect the performance of companion systems as a GNSS receiver (see section
for further details and design-in guidelines regarding Cellular / GNSS RF coexistence).
2.4.2
Cellular antenna RF interface (ANT)
2.4.2.1
General guidelines for antenna selection and design
The antenna is the most critical component to be evaluated. Designers must take care of the antenna
from all perspective at the very start of the design phase when the physical dimensions of the
application board are under analysis/decision, since the RF compliance of the device integrating
SARA-R4 series
modules with all the applicable required certification schemes depends on antenna’s
radiating performance.
Cellular antennas are typically available as:
•
External antennas (e.g. linear monopole):
o
External antennas basically do not imply physical restriction to the design of the PCB where
the SARA-R4 series module is mounted.
o
The radiation performance mainly depends on the antennas. It is required to select antennas
with optimal radiating performance in the operating bands.
o
RF cables should be carefully selected to have minimum insertion losses. Additional insertion
loss will be introduced by low quality or long cable. Large insertion loss reduces both transmit
and receive radiation performance.
o
A high quality 50
RF connector provides a clean PCB-to-RF-cable transition. It is
recommended to strictly follow the layout and cable termination guidelines provided by the
connector manufacturer.
•
Integrated antennas (e.g. PCB antennas such as patches or ceramic SMT elements):
o
Internal integrated antennas imply physical restriction to the design of the PCB: Integrated
antenna excites RF currents on its counterpoise, typically the PCB ground plane of the device
that becomes part of the antenna: its dimension defines the minimum frequency that can be
radiated. Therefore, the ground plane can be reduced down to a minimum size that should be
similar to the quarter of the wavelength of the minimum frequency that needs to be radiated,
given that the orientation of the ground plane relative to the antenna element must be
considered. As numerical example, the physical restriction to the PCB design can be
considered as following:
Frequency = 750 MHz
→
Wavelength = 40 cm
→
Minimum GND plane size = 10 cm
o
Radiation performance depends on the whole PCB and antenna system design, including
product 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.
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
