Realtek RTL8762C Hardware Instructions page 22

1. Trace width W:
Smaller W will lead to higher impedance.
2. Height from trace to ground H:
The impedance decreases when H is increased.
3. The gap between RF trace and adjacent ground G:
The impedance decreases when gap is decreases. Notice that gap must be symmetrical on
both sides of the trace.
4. Copper thickness t:
The impedance increases as thickness decreases.
5. Substrate dielectric constant:
Larger dielectric constant will leads to smaller impedance.
The above parameters for RF trace should be taken into consideration when designing the RF trace.
Several free impedance calculator software could be found online. Use these software to find out a
proper geometry design for RF trace.
The impedance must be constant throughout the RF signal trace. Therefore, trace width and the
gap between RF trace and adjacent ground should be maintained, and the copper skin laid at both
ends of the trace shall be intact.
Different from other signal traces, the RF trace must be guarded with ground, so that it forms a
CPWG guided wave structure. Any other traces must not be placed close to the RF trace.
Otherwise, mutual coupling between traces will cause severe interference problem.
RTL8762C Evaluation Board User Manual
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