HE910 Hardware User Guide
1VV0300925 Rev. 32 Page 55 of 111 2019-11-25
PCB Guidelines in case of FCC certification
In the case FCC certification is required for an application using HE910, HE910-D,
HE910-NAx, according to FCC KDB 996369 for modular approval requirements, the
transmission line has to be similar to that implemented on module’s interface board and
described in the following chapter.
6.6.1. Transmission line design
During the design of the interface board, the placement of components has been chosen
properly, in order to keep the line length as short as possible, thus leading to lowest power
losses possible. A Grounded Coplanar Waveguide (G-CPW) line has been chosen, since
this kind of transmission line ensures good impedance control and can be implemented in
an outer PCB layer as needed in this case. A SMA female connector has been used to
feed the line.
The interface board is realized on a FR4, 4-layers PCB. Substrate material is
characterized by relative permittivity εr = 4.6 ± 0.4 @ 1 GHz, TanD= 0.019 ÷ 0.026 @ 1
GHz.
A characteristic impedance of nearly 50 Ω is achieved using trace width = 1.1 mm,
clearance from coplanar ground plane = 0.3 mm each side. The line uses reference
ground plane on layer 3, while copper is removed from layer 2 underneath the line. Height
of trace above ground plane is 1.335 mm. Calculated characteristic impedance is 51.6 Ω,
estimated line loss is less than 0.1 dB. The line geometry is shown below:
Figure 6-1 Trasmission line designed
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