IP Mobilenet LLC B64450G25 ユーザーズマニュアル
SECTION 4: PRODUCT INSTALLATION
637246.DOC
Page
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Near-Field Exclusion Zone
The near-field exclusion zone (NFEZ) is the required distance between antennae to any other surfaces to
improve transmit and receive performance. The large radio frequency field that builts up around the
antenna upon transmitting is essential for proper data transmission. It can be severely corrupted by metal
objects in the NFEZ. As seen in the previous figure, the transmitting antenna is placed at the very top of
the tower especially if the base station will be required to transmit in all directions (omni-directional).
If the transmitting antenna cannot be positioned on the top of the tower and must be placed on
a tower arm, then it is important to realize that coverage will be shaded in the area behind the
tower from the anetnna. The installer must be certain that the area of desired coverage is
away from the tower and not behind it.
a tower arm, then it is important to realize that coverage will be shaded in the area behind the
tower from the anetnna. The installer must be certain that the area of desired coverage is
away from the tower and not behind it.
Receiving and transmitting antennae should not be on the same plane, especially VHF and
UHF systems where the frequency splits are relatiely small. An antenna in the near-field
exclusion zone that is tuned for the same frequency as the transmitting antenna will reradiate
the signal and create unwanted effects on the transmittal signal. The receivers will be
inundated by high levels of radio frequency energy from the transmitting antenna. This is
why it is important to include vertical separation in the plan for the base station installation.
The isolation provided by 30 feet of vertical spearation can dramatically improve the
performance of the base station.
UHF systems where the frequency splits are relatiely small. An antenna in the near-field
exclusion zone that is tuned for the same frequency as the transmitting antenna will reradiate
the signal and create unwanted effects on the transmittal signal. The receivers will be
inundated by high levels of radio frequency energy from the transmitting antenna. This is
why it is important to include vertical separation in the plan for the base station installation.
The isolation provided by 30 feet of vertical spearation can dramatically improve the
performance of the base station.
An antenna’s NFEZ can be calculated as follows:
D
=
2d
2
λ
Where:
D is the distance to the anenna’s near field boundary
d is the antenna’s longest linear dimension (in the same units as D)
λ
is the wavelength (in the same units as D)
Maximizing the distance between the receive antennae will provide maximum diversity gain and
will minimize antenna radiation pattern distortion.
will minimize antenna radiation pattern distortion.