WE866 HW User Guide
1VV0301330 Rev. 3
Page
31
of
54
2018-03-13
A 50Ω antenna is required. Telit’s WE866 interface features an SMA connector for an
external antenna, but other choices are possible, such as a chip or a printed one. In case
an integrated or printed antenna is used, it is recommended to place it on the edge of the
application board.
Since it may be necessary to tune the antenna impedance to 50Ω, it is recommended to
foresee a PI matching network between the WE866 and the antenna, at least during first
prototyping: if not required, a series 0Ω-resistor can be used, leaving the two shunt
components unpopulated.
In order to be able to reuse Telit’s FCC certification, the antenna on the application board
shall have a gain equal to the one recommended by Telit, or lower.
6.4.1.
PCB Design guidelines
The WE866 module provides a 50Ω antenna pad, which has to be routed to the antenna
connector (or the integrated antenna) by means of a transmission line.
It is vital that the impedance of this line is controlled to 50Ω. The line should be as short
as possible, and keep a constant cross section, without abrupt curves. It shall be isolated
from any other noise source: in particular, trace shall not be crossed by other lines in
adjacent layers. Instead, a continuous ground plane is recommended under the antenna
trace, and a ground via curtain should connect it to the coplanar ground planes.
As an example of a possible implementation, the details of the antenna trace on the WE866
interface board are described in this section.
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 of 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:
Summary of Contents for WE866
Page 1: ...04 2016 Mod 0805 2016 08 Rev 5 WE866 HW User Guide 1VV0301330 Rev 3 2018 03 13 13...
Page 10: ...WE866 HW User Guide 1VV0301330 Rev 3 Page 10 of 54 2018 03 13 Related Documents...
Page 33: ...WE866 HW User Guide 1VV0301330 Rev 3 Page 33 of 54 2018 03 13 7 MECHANICAL DESIGN Drawing...
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