User's Manual

HC25 Hardware Interface Overview
4 Antenna Interface
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HC25_HO_v00.220 Page 17 of 39 2007-03-20
Confidential / Preliminary
4 Antenna Interface
The RF interface has an impedance of 50Ω. HC25 is capable of sustaining a total mismatch at
the antenna connector or pad 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, DC-power consumption, modulation accuracy and harmonic suppression.
Antenna matching networks are not included on the HC25 PCB and should be placed in the
host application.
Regarding the return loss HC25 provides the following values in the active band:
The connection of the antenna or other equipment must be decoupled from DC voltage. This
is necessary because the antenna connector is DC coupled to ground via an inductor for ESD
protection.
Note: The antenna must be isolated for ESD protection (to withstand a voltage resistance up
to 8kV air discharge).
4.1 Antenna Installation
To suit the physical design of individual applications HC25 offers two alternative approaches
to connecting the antenna:
• Recommended approach: U.FL-R-SMT antenna connector from Hirose assembled on the
top side of the PCB. See Section 4.3 for connector details.
• Antenna pad and grounding plane placed on the bottom side. See Section 4.2.
The U.FL-R-SMT connector has been chosen as antenna reference point (ARP) for the Sie-
mens reference equipment submitted to type approve HC25. All RF data specified throughout
this manual are related to the ARP.
IMPORTANT: Both solutions can only be applied alternatively. This means, whenever an
antenna is plugged to the Hirose connector, the pad must not be used. Vice versa, if the
antenna is connected to the pad, then the Hirose connector must be left empty.
Table 6: 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
Idle <
5dB not applicable