LISA-U2 series - System Integration Manual
UBX-13001118 - R19
Early Production Information
Design-In
Page 130 of 175
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, to reduce as much as possible performance degradation due to
antenna mismatch, the following requirements should be met:
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 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