SARA-R4 series - System Integration ManualUBX-16029218 - R06 System descriptionPage 22 of 1021.7 Antenna interface1.7.1 Antenna RF interface (ANT)SARA-R4 series modules provide an RF interface for connecting the external antenna. The ANT pin representsthe 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 / Rxantenna through a 50 transmission line to allow proper RF transmission and reception.1.7.1.1 Antenna RF interfaces requirementsTable 7 summarizes the requirements for the antenna RF interface. See section 2.4.1 for suggestions to properlydesign antennas circuits compliant with these requirements.The antenna circuits affect the RF compliance of the device integrating SARA-R4 series moduleswith applicable required certification schemes (for more details see section 4). Compliance isguaranteed if the antenna RF interface requirements summarized in Table 7 are fulfilled.Item Requirements RemarksImpedance 50 nominal characteristic impedance The impedance of the antenna RF connection must match the 50 impedance of the ANT port.FrequencyRangeSee the SARA-R4 series Data Sheet [1] The required frequency range of the antenna connected to ANT portdepends on the operating bands of the used cellular module and theused mobile network.Return Loss S11 < -10 dB (VSWR < 2:1) recommendedS11 < -6 dB (VSWR < 3:1) acceptableThe Return loss or the S11, as the VSWR, refers to the amount ofreflected power, measuring how well the antenna RF connectionmatches the 50 characteristic impedance of the ANT port.The impedance of the antenna termination must match as much aspossible the 50 nominal impedance of the ANT port over theoperating frequency range, reducing as much as possible the amountof reflected power.Efficiency > -1.5 dB ( > 70% ) recommended> -3.0 dB ( > 50% ) acceptableThe radiation efficiency is the ratio of the radiated power to the powerdelivered to antenna input: the efficiency is a measure of how well anantenna receives or transmits.The radiation efficiency of the antenna connected to the ANT portneeds to be enough high over the operating frequency range tocomply with the Over-The-Air (OTA) radiated performancerequirements, as Total Radiated Power (TRP) and the Total IsotropicSensitivity (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 bythe directivity: the gain describes how much power is transmitted inthe direction of peak radiation to that of an isotropic source.The maximum gain of the antenna connected to ANT port must notexceed the herein stated value to comply with regulatory agenciesradiation 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 adequatemargin the maximum power transmitted by the modules.Table 7: Summary of Tx/Rx antenna RF interface requirements