Kelvin Hughes Limited SXV-A1 Manuel D’Utilisation
SharpEye™ SCV & SxV X-Band Radome Radar
Chapter 4: Positioning of radar equipment
KH-1650-CA issue 1
Page 16 of 60
Clearly, when the obstacle is as large or
larger than the antenna the radar becomes
completely blind although, as already
indicated, blind spots may still occur when
the obstacle is smaller than the antenna.
Whilst the most obvious features on a
vessel (SCV) leading to blockage are
masts, funnels, railings, etc.
Decks and cabin roofs can also cause
blockage if the antenna is not mounted
sufficiently high.
The same effect can occur when mounting the SxV on a building or mast.
REFLECTION: The drawing to the right shows a mast and antenna in plan
view, the mechanism of reflection is from an obstacle such as the mast.
Energy from the antenna is reflected in a different direction to that in which
the antenna is pointing. If this is incident on a target, then reflections from the
target will return via the same path.
If the reflections have sufficient magnitude they will produce a return on the
display in a direction corresponding to the pointing angle of the antenna, thus
producing a ghost target.
Antenna beam reflection by
a mast
The angular position of such ghost targets will be dependent on the shape of the obstacle and some
obstacles will produce ghost targets which are close to the real target, thus resulting in target
smearing. Masts and funnels will generally tend to produce distinct ghost targets and railings are likely
to lead to target smearing.
On some installations such as modern high speed vessels where a large portion of the deck or
mounting surface may be within the antennas vertical beamwidth, the radar signal is likely to be
reflected. Horizontal surfaces will tend to reflect the radar signal upwards away from other reflectors
causing no problem. Inclined or curved surfaces can reflect energy from the antenna into the
horizontal plane at a different angle to the pointing angle of the antenna. This can lead to ghost
returns and/ or target smearing.
Similar effects can occur on static or vehicle installations.
SEA & LAND CLUTTER
Sea and land clutter returns are not only dependent on the sea state but also on the height of the
radar antenna. As the antenna height increases so does the sea clutter returns and the range out to
which the sea clutter extends.
HORIZON RANGE
The curvature of the earth limits the range
that can be seen by a radar system.
The table opposite demonstrates the
approximate range to horizon on a generic
radar system.
Antenna height
above sea level
(metres)
Horizon range
(NM)
Horizon range
(km)
5.0m
5.0NM approx.
9.3km approx.
10m
7.0 NM approx.
13km approx.
15m
8.5 NM approx.
15.7km approx.
20m
10 NM approx.
18.5km approx.