Integration Manual

SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R11 Design-in Page 79 of 157
2.4 Antenna interface
SARA-R4/N4 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.
The ANT pin has a nominal characteristic impedance of 50  and must be connected to the physical
antenna through a 50  transmission line to allow clean transmission / reception of RF signals.
2.4.1 Antenna RF interface (ANT)
2.4.1.1 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/N4 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/N4 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.