SARA-R4 series - System integration manual
UBX-16029218 - R20 System description Page 32 of 128
C1-Public
1.7 Antenna interfaces
1.7.1 Cellular antenna RF interface (ANT)
SARA-R4 series modules provide an RF interface for connecting the external cellular antenna. The
ANT pin represents the primary RF input/output for transmission and reception of cellular RF signals.
The ANT pin has a nominal characteristic impedance of 50 and must be connected to the cellular
Tx / Rx antenna system through a 50 transmission line to allow clear RF transmission and reception.
1.7.1.1 Cellular antenna RF interface requirements
Table 7 summarizes the requirements for the antenna RF interface. See section 2.4.2 for suggestions
to correctly design antennas circuits compliant with these requirements.
⚠ The antenna circuits affect the RF compliance of the device integrating SARA-R4 series modules
with applicable required certification schemes (for more details see section 4). Compliance is
guaranteed if the antenna RF interface requirements summarized in Table 7 are fulfilled.
50 nominal characteristic
impedance
The impedance of the antenna RF connection must match the 50
impedance of the ANT port.
See the SARA-R4 series data
sheet [1]
The required frequency range of the antenna connected to ANT port
depends on the operating bands of the used cellular module and the
used mobile network.
S
11
< -10 dB (VSWR < 2:1)
recommended
S
11
< -6 dB (VSWR < 3:1)
acceptable
The Return loss or the S
11
, as the VSWR, refers to the amount of
reflected power, measuring how well the antenna RF connection
matches the 50 characteristic impedance of the ANT port.
The impedance of the antenna termination must match as much as
possible the 50 nominal impedance of the ANT port over the
operating frequency range, reducing as much as possible the amount
of reflected power.
> -1.5 dB ( > 70% ) recommended
> -3.0 dB ( > 50% ) acceptable
The radiation efficiency is the ratio of the radiated power to the
power delivered to antenna input: the efficiency is a measure of how
well an antenna receives or transmits.
The radiation efficiency of the antenna connected to the ANT port
needs to be enough high over the operating frequency range to
comply with the Over-The-Air (OTA) radiated performance
requirements, as Total Radiated Power (TRP) and the Total Isotropic
Sensitivity (TIS), specified by applicable related certification
schemes.
According to radiation exposure
limits
The power gain of an antenna is the radiation efficiency multiplied by
the directivity: the gain describes how much power is transmitted in
the direction of peak radiation to that of an isotropic source.
The maximum gain of the antenna connected to ANT port must not
exceed the herein stated value to comply with regulatory agencies
radiation exposure limits. For additional info see sections 4.2.2.
> 24 dBm ( > 0.25 W ) for R410M
> 33 dBm ( > 2.0 W ) for R412M /
R422 / R422S / R422M8S
The antenna connected to the ANT port must support with adequate
margin the maximum power transmitted by the modules.
Table 7: Summary of Tx/Rx antenna RF interface requirements
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