u-blox SARA-G3 Series System Integration Manual page 119

 Additional components (R1, C1 and D1 in
ESD protection

The ANT pin must be connected to the antenna connector by means of a transmission line with
nominal characteristics impedance as close as possible to 50 
The DC impedance at RF port for some antennas may be a DC open (e.g. linear monopole) or a DC
short to reference GND (e.g. PIFA antenna). For those antennas, without the diagnostic circuit of
41Figure 41, the measured DC resistance is always at the limits of the measurement range (respectively
open or short), and there is no mean to distinguish between a defect 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.
It is recommended to use an antenna with a built-in diagnostic resistor in the range from 5 k to
30 k 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 a GSM antenna with built-in DC load resistor of 15 k. 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 k to 17 k
if a 15 k diagnostic resistor is used) indicate that the antenna is properly connected
 Values close to the measurement range maximum limit (approximately 50 k) or an open-circuit
"over range" report (see
connected or the RF cable is broken

Reported values below the measurement range minimum limit (1 k) 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
improper connection, damaged antenna or wrong value of antenna load resistor for diagnostic
 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
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  transmission line as described in
UBX-13000995 - R06
Figure 41Figure
u-blox AT Commands Manual
Figure 40Figure
Objective Specification
SARA-G3 series - System Integration Manual
41) are needed at the ANT_DET pin as
[2]) means that that the antenna is not
40.
Formatted: English (U.S.)
Figure
Design-in
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