Hardware Design V1.0

NB-IoT Module Series
BC95 Hardware Design
BC95_Hardware_Design Confidential / Released 30 / 45
4.1.1. Impedance Control for RF Trace
The RF trace in host PCB connected to the module RF antenna pad should be coplanar waveguide line or
microstrip line, whose characteristic impedance should be set to 50Ω. It is recommended to use coplanar
waveguide line. The characteristic impedance of coplanar waveguide line could been affected by many
factors, such as dielectric constant, distance between signal layer and reference ground(H), line width(W),
clearance between line and ground(S), copper foil thicknesses(T). The relative relationship between
those parameters could be obtained through software like CITS25, shown as follows.
Figure 17: Coplanar Waveguide Line Structure (Software Calculation)
The reference ground would be different for different host PCB. It should set the top layer as RF trace and
set bottom layer as reference ground for two-layer PCB, as shown in following figure.
Figure 18: Layout for Two-layer PCB
For four-layer PCB, it should choose the second layer, third layer or bottom layer as reference ground.
The area located in the layer between RF trace and reference ground should be kept out. And the width of
that area should be five times wider than RF trace at least. Just as shown in figures below. It is the same
with other multi-layer PCBs.
Quectel
Confidential