Quectel FC905A User Manual page 33

Figure 10: Coplanar Waveguide Design on a 4-layer PCB (Layer 3 as Reference Ground)
Figure 11: Coplanar Waveguide Design on a 4-layer PCB (Layer 4 as Reference Ground)
To ensure RF performance and reliability, the following principles should be complied with RF layout
design:
 Use impedance simulation tool to control the characteristic impedance of RF traces to 50 Ω.

The GND pins adjacent to RF pins should not be designed as thermal relief pins, and should be fully
connected to ground.

The distance between the RF pins and the RF connector should be as short as possible, and all the
right-angle traces should be changed to curved ones. The recommended trace angle is 135° .

There should be clearance area under the signal pin of the antenna connector or solder joint.

The reference ground of RF traces should be complete. Meanwhile, adding some ground vias around
RF traces and the reference ground could help to improve RF performance. The distance between
the ground vias and RF traces should be no less than two times the width of RF signal traces (2 × W).

Keep RF traces away from interference sources, and avoid intersection and paralleling between
traces on adjacent layers.
For more details about RF layout, see document [2].
FC905A_Hardware_Design
Wi-Fi&Bluetooth Module Series
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