Alcatel-Lucent 9500 MXC User Manual page 308

Chapter 5. Antenna Alignment
Procedure for Dual Polarized Antennas
Vol. III-5-8
While a dual-feed antenna may be specified with a cross polarization
discrimination of 30 dB, unless the antenna-to-antenna alignment over a link is
correct, the effective discrimination can be significantly less.
• The horizontal-to-vertical receive signal discrimination for satisfactory XPIC
operation must not be less than 20 dB, and where possible should be set for
optimum discrimination using this procedure.
• High performance shielded antennas typically exhibit 30 dB cross polarization
discrimination whereas 40 dB is typical for purpose-designed, high polarization
discrimination antennas.
• The received-signal V and H discrimination can be checked using the
Diagnostics > Performance screen. The cross pole discrimination entry
measures the V and H signal discrimination in dB at the input to the RAC 40s
(from the antenna feeds). The improvement in signal discrimination provided
by the RAC 40 XPIC function is in addition to this measurement.
This alignment procedure is intended for dual-polarized antennas, but is also
generally applicable to installations using separate antennas for V and H planes.
Where protected XPIC links are installed (dual ODUs on a common feed) an
equal-loss coupler must be used.
XPIC links must be configured for identical frequency, Tx power and
bandwidth/modulation, and ATPC must not be used.
The following alignment procedure details steps required to:
• Check and if necessary set feedhead alignment using a spirit level.
• Align the antennas at each end using just one of the feeds, H or V. (Standard
co-plane antenna alignment).
• Where the V and H waveguide ports on an antenna are not marked they can
be identified by the orientation of the waveguide slots. Refer to Setting the
Polarization in Volume III, Chapter 2.
• Where a dual-polarized antenna presents the same orientation on both ports,
one should have a straight waveguide feed to the antenna feedhead, the other
will include a 90 degree twist or have a straight waveguide feed but with a
polarization rotator in the feedhead. Generally the polarization rotator will
act on the outer-most waveguide on the feedhead.
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