Integration Manual
SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R13 Design-in Page 58 of 119
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 Ω and must be connected to the physical antenna through a
50 Ω 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 Ω 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
In both of cases, selecting external or internal antennas, these recommendations should be observed:
• Select an antenna providing optimal return loss (or VSWR) figure over all the operating frequencies.
• Select an antenna providing optimal efficiency figure over all the operating frequencies.
• Select an antenna 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).