User's Manual

CL865-DUAL Hardware User Guide
1vv0301104 Rev.1 – 2014-03-07
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Reserved. Page 33 of 70
Mod. 0805 2011-07 Rev.2
7.2. PCB Guidelines in case of FCC certification
In the case FCC certification is required for an application using CL865, according to FCC
KDB 996369 for modular approval requirements, the transmission line has to be similar to
that implemented on CL865 interface board and described in the following chapter.
7.2.1. Transmission line design
During the design of the CL865 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: