User's Manual

EHS5-E/EHS5-US Hardware Interface Overview
2.2 RF Antenna Interface
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EHS5_HIO_v01.000 Page 16 of 35 2012-11-14
Confidential / Preliminary
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2.2 RF Antenna Interface
The RF interface has an impedance of 50. EHS5-E/EHS5-US is capable of sustaining a total
mismatch at the antenna line without any damage, even when transmitting at maximum RF
power.
The external antenna must be matched properly to achieve best performance regarding radi-
ated power, modulation accuracy and harmonic suppression. Antenna matching networks are
not included on the EHS5-E/EHS5-US module and should be placed in the host application if
the antenna does not have an impedance of 50
.
Regarding the return loss EHS5-E/EHS5-US provides the following values in the active band:
2.2.1 Antenna Installation
The antenna is connected by soldering the antenna pad and its neighboring ground pads di-
rectly to the application’s PCB. The antenna pad is the antenna reference point (ARP) for
EHS5-E/EHS5-US. All RF data specified throughout this document is related to the ARP.
The distance between the antenna pad and its neighboring GND pads has been optimized for
best possible impedance. On the application PCB, special attention should be paid to these
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
 line impedance. Line width and distance to the GND plane needs
to be optimized with regard to the PCB’s layer stack.
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.
For type approval purposes, the use of a 50
 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 EHS5-E/EHS5-US‘s antenna pad.
Table 3: Return loss in the active band
State of module Return loss of module Recommended return loss of application
Receive >
8dB > 12dB
Transmit not applicable >
12dB