User's Manual

SARA-R4 series - System Integration Manual
UBX-16029218 - R03 System description
Page 21 of 94
1.7 Antenna interface
1.7.1 Antenna RF interface (ANT)
SARA-R4 series modules provide an RF interface for connecting the external antenna. The ANT pin represents
the primary RF input/output for transmission and reception of LTE RF signals.
The ANT pin has a nominal characteristic impedance of 50  and must be connected to the primary Tx / Rx
antenna through a 50  transmission line to allow proper RF transmission and reception.
1.7.1.1 Antenna RF interfaces requirements
Table 7 summarizes the requirements for the antenna RF interface. See section 2.4.1 for suggestions to properly
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.
Item
Requirements
Remarks
Impedance
50  nominal characteristic impedance
The impedance of the antenna RF connection must match the 50 
impedance of the ANT port.
Frequency
Range
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.
Return Loss
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.
Efficiency
> -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.
Maximum Gain
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.
Input Power
> 24 dBm ( > 0.25 W )
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