User's Manual

7.3. PCB Guidelines in case of FCC certification
In the case FCC certification is required for an application using GE865, according to FCC KDB
996369 for modular approval requirements, the transmission line has to be similar to that
implemented on GE865 interface board and described in the following chapter.
7.3.1. Transmission line design
During the design of the GE865 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 ε
r
= 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:
0.3 mm
0.035 mm
0.3 mm
6.2 mm
FR4
0.035 mm
0.035 mm
1.335 mm
0.2 mm
1.1 mm
L3
L2
L1
1.1 mm