User's Manual

DE910 Series Hardware User Guide
1vv0301183 Rev.1 – 2015-2-13
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Reserved. Page 36 of 70
 Keep the antenna line far away from the DE921 power supply lines.
 If EM noisy devices are present on the PCB hosting the DE921, such as fast switching
ICs, take care of shielding them with a metal frame cover.
 If EM noisy devices are not present around the line, use of geometries like Micro strip
or Grounded Coplanar Waveguide are preferred since they typically ensure less
attenuation when compared to a Strip line having same length.
6.1.2. PCB Guidelines in case of FCC
certification
In the case FCC certification is required for an application using DE921, 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.
6.1.2.1.1.1. Transmission line design
During the design of the DE921 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: