Reference Design; Reference Design Of Rf Routing - Quectel FC905A User Manual

Wi-Fi&Bluetooth Module Series

3.8.3. Reference Design

FC905Amodule provides an RF antenna pin for Wi-Fi/Bluetooth antenna connection. The RF trace in host
PCB connected to the module's RF antenna pin should be microstrip line or other types of RF trace, with
characteristic impendence close to 50 Ω. FC905A comes with grounding pins which are next to the
antenna pin in order to give a better grounding.
A reference circuit for the RF antenna interface is shown below. It is recommended to reserve a LC and
Π-type matching circuit for better RF performance. Matching components should be placed as close to
the antenna as possible. The NM in the figure below is not attached by default.
When using the PCB antenna on the module, place the module near the PCB of the mainboard. Ensure
that the distance between the PCB of the mainboard and other metal components, connectors, PCB via
holes, cabling, and copper coating is at least 16 mm. Ensure that all layers of the PCB area of the
mainboard under the PCB antenna are cleared.

3.8.4. Reference Design of RF Routing

For user's PCB, the characteristic impedance of all RF traces should be controlled to 50 Ω. The
impedance of the RF traces is usually determined by the trace width (W), the materials' dielectric constant,
the height from the reference ground to the signal layer (H), and the spacing between RF traces and
grounds (S). Microstrip or coplanar waveguide is typically used in RF layout to control characteristic
impedance. The following are reference designs of microstrip or coplanar waveguide with different PCB
structures.
Figure 8: Microstrip Design on a 2-layer PCB
Figure 9: Coplanar Waveguide Design on a 2-layer PCB
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