LENA-R8 series - System integration manual
UBX-22015376 - R02
Design-in
Page 65 of 116
C1-Public
Application Board
Antenna Cable
LENA-R8 series
56
ANT
59
ANT_DET
R1
C1
D1
C2
J1
Z
0
= 50 ohm
Z
0
= 50 ohm
Z
0
= 50 ohm
Cellular Antenna Assembly
R2
C3
L2
Radiating
Element
Diagnostic
Circuit
L1
Figure 43: Suggested schematic for antenna detection circuit on application PCB and diagnostic circuit on antenna assembly
Reference
Description
Part number - manufacturer
C1
27 pF Capacitor Ceramic C0G 0402 5% 50 V
GRM1555C1H270J - Murata
C2
33 pF Capacitor Ceramic C0G 0402 5% 50 V
GRM1555C1H330J - Murata
D1
Very Low Capacitance ESD Protection
PESD0402-140 - Tyco Electronics
L1
68 nH Multilayer Inductor 0402 (SRF ~1 GHz)
LQG15HS68NJ02 - Murata
R1
10 k
Resistor 0402 1% 0.063 W
Various Manufacturers
J1
Connector 50
Various Manufacturers
C3
22 pF Capacitor Ceramic C0G 0402 5% 25 V
GRM1555C1H220J - Murata
L2
68 nH Multilayer Inductor 0402 (SRF ~1 GHz)
LQG15HS68NJ02 - Murata
R2
15 k
Resistor for Diagnostic
Various Manufacturers
Table 31: Example of parts for antenna detection circuit on application PCB and diagnostic circuit on antenna assembly
The antenna detection circuit and diagnostic circuit suggested in
explained here:
•
When antenna detection is forced by the AT+UANTR command,
ANT_DET
generates a DC current
measuring the resistance (R2) from the antenna connectors (J1) provided on the application
board to GND.
•
DC blocking capacitors are needed at the
ANT
pins (C2) and at the antenna radiating element (C3)
to decouple the DC current generated by the
ANT_DET
pin.
•
Choke inductors with a Self-Resonance Frequency (SRF) in the range of 1 GHz are needed in series
at the
ANT_DET
pin (L1) and in series at the diagnostic resistor (L2), to avoid a reduction of the
RF performance of the system, improving the RF isolation of the load resistor.
•
Additional components (R1, C1 and D1 in
) are needed at the
ANT_DET
pin as 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 the 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
, the measured DC resistance is always at the limits of the measurement range (respectively
open or short), and there is no means to distinguish between a defect on the antenna path with similar
characteristics (respectively: removal of linear antenna or RF cable shorted to GND for a PIFA
antenna).
Furthermore, any other DC signal injected to the RF connection from an ANT connector to a 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.
