Site considerations
98-175666-A
Chapter 2: Installation
2-16
2.2.4 Interference from radar, GPS/GNSS, L-band and other transmitters
The ship’s radar and high power radio transmitters may compromise the ADU performance.
RF emission from radars might actually damage the ADU. The ADU itself may also interfere
with other radio systems.
Radar
It is difficult to give exact guidelines for the minimum distance between a radar and the
ADU because radar power, radiation pattern, frequency and pulse length/shape vary from
radar to radar. Further, the ADU is typically placed in the near field of the radar ADU and
reflections from masts, decks and other items in the vicinity of the radar are different from
ship to ship. But it is possible to give a few guidelines. Since a radar radiates a fan beam with
a horizontal beam width of a few degrees and a vertical beam width of up to +/- 15°, the
worst interference can be avoided by mounting the ADU at a different level – meaning that
the ADU is installed minimum 15° above or below the radar antenna. Due to near field
effects the benefit of this vertical separation could be reduced at short distances (below
approximately 10 m) between radar antenna and the ADU. Therefore it is recommended to
ensure as much vertical separation as possible when the ADU has to be placed close to a
radar antenna.
The minimum acceptable separation (d min.) between a radar and the ADU is determined
by the radar wavelength/frequency and the power emitted by the radar. The tables below
show some “rule of thumb” minimum separation distances as a function of radar power at X
and S band. If the d min. separation listed below is applied, antenna damage is normally
avoided. The separation distance for C-band (4-8 GHz) radars should generally be the same
as for S-band and X-band radars.
“d min.” is defined as the shortest distance between the radar antenna (in any position) and
the surface of the ADU.
Note
Do not place the antenna close to interfering signal sources or receivers. For
allowed distances to other transmitters see Figure 2-18. It is recommended to
test the total system by operating all equipment simultaneously and verifying
that there is no interference.
Figure 2-17: Interference with the vessel’s radar
Min. 15°
Min. 15°
Radar
d min
