User's Manual

Cinterion
®
ELS31-/ELS51-US Hardware Interface Overview
2.2 RF Antenna Interface
29
 ELS31-US_ELS51-US_HIO_v01.000a 2016-12-28
Confidential / Preliminary
Page 21 of 46
2.2.1 Antenna Installation
The antenna is connected by soldering the antenna pads (RF_OUT, pad #59 and DIV_ANT,
pad 56) its neighboring ground pads (GND, i.e., pads #55, #57, #58 and #60) directly to the
application’s PCB. The antenna pad is the antenna reference point (ARP) for ELS31-US/ELS51-
US. All RF data specified throughout this document is related to the ARP.
The distance between the antenna RF pads and its neighboring GND pads has been optimized
for best possible impedance. On the application PCB, special attention should be paid to these
3 pads, in order to prevent mismatch.
The wiring of the antenna connection line, starting from the antenna pad to the application an-
tenna should result in a 50
Ω line impedance. Line width and distance to the GND plane needs
to be optimized with regard to the PCB’s layer stack. Some examples are given in Section
2.2.2.
To prevent receiver desensitization due to interferences generated by fast transients like high
speed clocks on the application PCB, it is recommended to realize the antenna connection line
using embedded Stripline rather than Micro-Stripline technology. Please see Section 2.2.2.2
for an example.
For type approval purposes, the use of a 50
Ω coaxial antenna connector (U.FL-R-SMT) might
be necessary. In this case the U.FL-R-SMT connector should be placed as close as possible
to ELS31-US/ELS51-US‘s antenna pad.