User's Manual

UL865-N3G Hardware User Guide
1VV0301177 Rev 2– 2015-04-20
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights
Reserved. Page 35 of 70
Mod. 0805 2011-07 Rev.2
7.8. PCB Guidelines in case of FCC certification
In the case FCC certification is required for an application using UL865-N3G V2, according
to FCC KDB 996369 for modular approval requirements, the transmission line has to be
similar to that implemented on UL865-N3G V2 interface board and described in the following
chapter.
7.8.1. Transmission line design
During the design of the UL865-N3G V2 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: