Integration Manual

SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R13 Design-in Page 66 of 119
on antenna path with similar characteristics (respectively: removal of linear antenna or RF cable shorted to GND for PIFA
antenna).
Furthermore, any other DC signal injected to the RF connection from ANT connector to radiating element will alter the
measurement and produce invalid results for antenna detection.
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☞ It is recommended to use an antenna with a built-in diagnostic resistor in the range from 5 kΩ to 30 kΩ to assure
good antenna detection functionality and avoid a reduction of module RF performance. The choke inductor should
exhibit a parallel Self Resonance Frequency (SRF) in the range of 1 GHz to improve the RF isolation of load resistor.
For example:
Consider an antenna with built-in DC load resistor of 15 kΩ. Using the +UANTR AT command, the module reports the
resistance value evaluated from the antenna connector provided on the application board to GND:
• Reported values close to the used diagnostic resistor nominal value (i.e. values from 13 kΩ to 17 kΩ if a 15 kΩ
diagnostic resistor is used) indicate that the antenna is correctly connected.
• Values close to the measurement range maximum limit (approximately 50 kΩ) or an open-circuit “over range” report
(see the SARA-R4/N4 series AT Commands Manual [2]) means that that the antenna is not connected or the RF cable
is broken.
• Reported values below the measurement range minimum limit (1 kΩ) highlights a short to GND at antenna or along
the RF cable.
• Measurement inside the valid measurement range and outside the expected range may indicate an unclean
connection, a damaged antenna or incorrect value of the antenna load resistor for diagnostics.
• Reported value could differ from the real resistance value of the diagnostic resistor mounted inside the antenna
assembly due to antenna cable length, antenna cable capacity and the used measurement method.
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☞ If the antenna detection function is not required by the customer application, the ANT_DET pin can be left not
connected and the ANT pin can be directly connected to the antenna connector by means of a 50 Ω transmission line
as described in Figure 34.