LE940B6 HW User Guide
Rev. 2.02
Page 68 of 111
2020-01-10
Secondary Antenna Requirements
This product includes an input for a second Rx antenna to improve radio sensitivity. The
function is called Antenna Diversity.
Since there is no antenna connector on the LE940B6 module, the antenna must be
connected to the LE940B6 antenna pad by means of a transmission line implemented on
the PCB.
If the antenna is not directly connected at the antenna pad of the LE940B6 (AU9), a PCB
line is required to connect to it or to its connector.
The second Rx antenna must not be located in close vicinity of the main antenna. To
improve diversity gain and isolation and to reduce mutual interaction, the two antennas
should be located at the maximum reciprocal distance possible, taking into consideration
the available space within the application.
NOTE:
If Rx Diversity is not used/connected, disable the Diversity functionality using
the AT+XRXDIV command (refer to Ref 1: LE940B6 AT Command
Reference Guide) and connect the Diversity pad AU9 to a 50 Ohm
termination.
PCB Guidelines in Case of FCC Certification
If FCC certification is required for an application using LE940B6-NA, according to FCC
KDB 996369 for modular approval requirements, the transmission line must be similar to
the one implemented on the
module’s interface board and described in the following
chapter.
7.5.1.
Transmission Line Design
During the design of the interface board, the placement of components has been chosen
properly 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.
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