Specifications

XT55 Hardware Interface Description
Confidential / Preliminary
s
mo b i l e
XT55_hd_v00.02 Page 78 of 116 17.03.2004
5 GSM and GPS antenna interfaces
5.1 GSM antenna installation
The RF interface has an impedance of 50". XT55 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
radiated power, DC-power consumption and harmonic suppression. Matching networks are
not included on the XT55 PCB and should be placed in the host application.
Regarding the return loss XT55 provides the following values:
Table 20: Return loss
State of module Return loss of module Recommended return loss of application
Receive > 8dB > 12dB
Transmit not applicable > 12dB
Idle < 5dB not applicable
The connection of the antenna or other equipment must be decoupled from DC voltage.
5.1.1 GSM antenna connector
To suit the physical design of individual applications XT55 offers two alternative approaches
to connecting the GSM antenna:
· Recommended approach: U.FL-R-SMT antenna connector from Hirose assembled on
the component side of the PCB (top view on XT55). See Chapter 5.3 for details.
· Antenna pad and grounding plane placed on the bottom side. See Chapter 5.1.2.
Figure 33: U.FL-R-SMT connector Figure 34: Antenna pad and GND plane
Antenna pad
Antenna ground