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FIBOCOM NL668-AM Hardware User Manual
Page 46 of 62
Figure 4-2 shows the reference circuit design for the GNSS antenna. These matches need to be placed
close to the antenna:
Figure 4-2 GNSS RF Reference Circuit
Make sure the characteristic impedance of the transmission cable is 50 ohms.
Since the antenna cable loss is less than 0.3dB, keep the PCB cable as short as possible.
Keep the PCB LAYOUT as straight as possible, and reduce holes on the route to another layer; also
avoid right-angle and acute-angle wiring.
PCB cable should have a good reference ground to avoid other signal cable near the antenna.
Recommend a complete ground level, and use this complete ground level as a reference ground.
The ground around the antenna must be connected to the main ground through the holes placed near the
edge of the ground and tracking the cable route.
Note:
Refer to the document
《
FIBOCOM_RF Antenna Application Design Instruction
》
for specific
design
4.6 Antenna Design
1) Antenna efficiency
Antenna efficiency is the ratio of antenna input power to emissivity. Due to the antenna return loss,
material loss, and coupling loss, the radiated power is always lower than the input power. Recommend>
40% (-4dB).
2) S11 or VSWR
S11 shows that the matching degree of the antenna’s 50 ohm impedance, to a certain extent, affects the
antenna efficiency. VSWR test methods can be used to measure this parameter. Recommend S11
<-10dB.
