Integration Manual

Table Of Contents
LISA-U2 series - System Integration Manual
UBX-13001118 - R25 Design-In Page 134 of 182
2.4.1 Antenna termination
The LISA-U2 modules are designed to work on a 50 load. However, real antennas have no perfect 50
load on all the supported frequency bands. Therefore the following requirements should be met in
order to reduce the performance degradation due to antenna mismatch as much as possible:
Measure the antenna termination with a network analyzer: connect the antenna through a coaxial
cable to the measurement device, the |S
11
| indicates which portion of the power is delivered to the
antenna and which portion is reflected by the antenna back to the module output.
A good antenna should have an |S
11
| below -10 dB over the entire frequency band. Due to
miniaturization, mechanical constraints and other design issues, this value will not be achieved. An
|S
11
| value of about -6 dB - (in the worst case) - is acceptable.
Figure 63 shows an example of this measurement:
Figure 63: |S
11
| sample measurement of a penta-band antenna that covers in a small form factor the 4 GSM bands (850 MHz,
900 MHz, 1800 MHz and 1900 MHz) and the UMTS Band I
Figure 64 shows comparable measurements performed on a wideband antenna. The termination is
better, but the size of the antenna is considerably larger.
Figure 64: |S
11
| sample measurement of a wideband antenna