ISO 8729-2:2009
(Main)Ships and marine technology — Marine radar reflectors — Part 2: Active type
Ships and marine technology — Marine radar reflectors — Part 2: Active type
It is recognised that small vessels, often made of glass fibre reinforced plastic (GRP), can be poor reflectors of radar signals. In situations where radar is the prime observation tool used by ships at sea, the International Maritime Organisation considers that it is essential that small vessels, considered in this context to be those under 150 gross tonnage, be equipped with a radar reflector to enhance their radar return and thus improve their visibility to radar. ISO 8729-2:2009 specifies the minimum requirements for a radar reflector intended to enhance returns from small vessels as required by IMO Resolution MSC.164(78). It provides the specification for the construction, performance, testing, inspection and installation of such radar reflectors.
Navires et technologie maritime — Réflecteurs radars de marine — Partie 2: Type actif
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 8729-2
First edition
2009-06-01
Ships and marine technology — Marine
radar reflectors —
Part 2:
Active type
Navires et technologie maritime — Réflecteurs radars de marine —
Partie 2: Type actif
Reference number
ISO 8729-2:2009(E)
©
ISO 2009
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ISO 8729-2:2009(E)
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ii © ISO 2009 – All rights reserved
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ISO 8729-2:2009(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Construction. 3
4.1 General arrangement. 3
4.2 Structure and materials. 4
4.3 Enclosed size of the reflector. 4
4.4 Mass of the reflector. 4
5 Performance . 4
5.1 Functionality. 4
5.2 Reflecting pattern . 4
5.3 Time delay and stretching . 5
5.4 Polarisation . 5
5.5 Stability and self-oscillation . 5
5.6 Maximum power. 6
5.7 Tolerance to a radar in close proximity. 6
6 Environmental requirements . 6
7 Inspection and type tests. 6
7.1 Inspection . 6
7.2 Testing . 6
7.3 Performance tests. 6
7.4 Environmental tests. 12
7.5 Mechanical strength test. 13
7.6 Electromagnetic emission tests. 13
7.7 Electromagnetic immunity tests . 13
7.8 Spurious emissions tests . 13
8 Installation . 13
8.1 Method . 13
8.2 Positioning . 13
8.3 Mounting height. 14
8.4 Mass . 14
8.5 Size. 14
9 Manual. 14
10 Marking . 15
Annex A (normative) Guidance notes for the installation of active radar reflectors . 16
Annex B (normative) Test method for unwanted emissions of active radar reflectors. 18
Bibliography . 23
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ISO 8729-2:2009(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 8729-2 was prepared by Technical Committee ISO/TC 8, Ships and marine technology, Subcommittee
SC 6, Navigation and ship operations.
ISO 8729 consists of the following parts, under the general title Ships and marine technology — Marine radar
reflectors:
⎯ Part 1: Passive type
⎯ Part 2: Active type
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INTERNATIONAL STANDARD ISO 8729-2:2009(E)
Ships and marine technology — Marine radar reflectors —
Part 2:
Active type
1 Scope
It is recognised that small vessels, often made of glass fibre reinforced plastic (GRP), can be poor reflectors of
radar signals. In situations where radar is the prime observation tool used by ships at sea, the International
Maritime Organisation considers that it is essential that small vessels, considered in this context to be those
under 150 gross tonnage, be equipped with a radar reflector to enhance their radar return and thus improve
their visibility to radar.
This International Standard specifies the minimum requirements for a radar reflector intended to enhance
returns from small vessels as required by IMO Resolution MSC.164(78).
It provides the specification for the construction, performance, testing, inspection and installation of such radar
reflectors.
NOTE Requirements that have been extracted from IMO Resolution MSC.164(78) Revised performance standards
for radar reflectors are printed in italics.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 17025, General requirements for the competence of testing and calibration laboratories
IEC 60945, Marine navigation and radiocommunication equipment and systems — General requirements —
Methods of testing and required test results
ITU-R SM.329, Unwanted emissions in the spurious domain
ITU-R SM.1541, Unwanted emissions in the out-of-band domain
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
radar reflector
device that is designed to enhance radar returns from vessels with small radar cross section
3.2
active radar reflector
device that receives, amplifies and retransmits a radar signal as a method of enhancing radar returns
NOTE An active radar reflector is often also known as a radar target enhancer (RTE).
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ISO 8729-2:2009(E)
3.3
radar cross section
RCS
equivalent echoing area which is 4 π times the ratio of the power per unit solid angle scattered in a specified
direction to the power per unit area in a plane wave incident on the scatterer from a specified direction
NOTE It is dependent on the radar operating frequency and the three-dimensional orientation of the reflector.
Polarization of the transmitter and the received wave affects the effective radar cross section of the reflector.
3.4
azimuthal polar diagram
polar diagram providing the RCS of the reflector with respect to its azimuthal angle
NOTE These diagrams can be produced for any angle of heel.
3.5
null
pronounced fall-off of RCS in the azimuthal polar diagram
3.6
stated performance level
SPL
performance level calculated from measurement data sets (i.e. azimuthal polar diagrams) taken during
technical measurements of reflective performance
NOTE 1 SPL is the RCS value at which a null is 10° wide (see Figure 1). If there is more than one null with a width of at
least 10°, then SPL is the lowest such value.
NOTE 2 If the azimuthal polar diagram does not show a null (as defined in 3.5) that is 10° wide, then the SPL is the
RCS which is achieved over 280° of azimuth.
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ISO 8729-2:2009(E)
Key
A azimuth
R radar cross section
a
Stated performance level.
b
Null width u 10°.
c
Spacing between nulls W 20°.
Figure 1 — Definition of stated performance level
3.7
self-oscillation
phenomenon whereby the receive and transmit antennas of an active reflector are unintentionally coupled,
either inherently or by a reflecting surface closeby, so that feedback occurs between the two
NOTE Devices that are self-oscillating are also said to be unstable.
3.8
saturation
state whereby an active radar reflector is emitting the maximum power of which it is capable
NOTE 1 This power at which saturation occurs is known as the saturated power.
NOTE 2 The distance from the interrogating radar at which saturation occurs is a function of the power of the radar, the
total gain of the reflector and the maximum power of the reflector.
4 Construction
4.1 General arrangement
The active radar reflector shall consist of a receive antenna (or antennas), an amplifier (or amplifiers) capable
of operation across the X and S bands and a transmit antenna (or antennas). Typically there may also be an
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ISO 8729-2:2009(E)
associated control box whose function is to switch the device on and off and to indicate to the user that the
device is working.
4.2 Structure and materials
The materials used for the radar reflector shall be of sufficient strength and quality as to make the reflector
capable of maintaining reflection performance under the conditions of stress due to sea states, vibration,
humidity and change of temperature likely to be experienced in the marine environment. Use of ferrous metals
should be avoided.
4.3 Enclosed size of the reflector
3
The volume of the reflector should not exceed 0,05 m .
4.4 Mass of the reflector
The reflector should weigh as little as practical in order to minimise its effect on the stability of small vessels.
5 Performance
5.1 Functionality
The active radar reflector shall receive a radar pulse, amplify it and retransmit it. The output shall only be an
amplified version of the received pulse, without any form of processing except limiting.
5.2 Reflecting pattern
2
5.2.1 The radar reflector shall have a stated performance level of at least 7,5 m at X band (9,300 GHz to
2
9,500 GHz) and 0,5 m at S band (2,900 GHz to 3,100 GHz). The SPL shall be maintained over a total angle
of at least 280°.
The response shall, at the calculated SPL for each azimuthal polar diagram,
⎯ not have any nulls wider than a single angle of 10°, and
⎯ not have a distance between nulls of less than 20°. Nulls of less than 5° shall be ignored for this
calculation.
NOTE Typical azimuthal polar diagrams for an active radar reflector in X band at 0° and 10° elevation are given in
Figure 2.
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ISO 8729-2:2009(E)
Key
A azimuth
2
R radar cross section, expressed in m
a
0° elevation
b 2
stated performance level for 21,7 m
c
10° elevation
d 2
stated performance level for 7,5 m
3
The 0° elevation response shows a calculated SPL of 21,7 m for 280° azimuth coverage and the response at
3
10° elevation is calculated at 7,5 m , which is just compliant with respect to the minimum SPL requirement.
These two plots also illustrate the expected antenna gain reduction with elevation change.
Figure 2 — Examples of typical RTE azimuthal polar diagrams and their associated SPL
5.2.2 For power-driven vessels and sailing vessels designed to operate with little heel (catamaran/trimaran),
this performance shall be maintained through angles of (athwartships) heel 10° either side of vertical. For
other vessels, the reflector shall maintain this performance over 20° either side of vertical.
5.3 Time delay and stretching
The time delay and stretching of the output shall not exceed 10 % of the length of the received pulse or 10 ns,
whichever is greater.
5.4 Polarisation
The active reflector shall respond to radar using horizontal polarisation in both X and S bands. For S band, the
active reflector may use circular polarised antennas for receiving and transmitting.
5.5 Stability and self-oscillation
The active reflector shall be inherently stable and it shall not be possible for instability to be induced under any
conditions. Stability shall be demonstrated by the tests specified in 7.3.4 and 7.3.5.
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ISO 8729-2:2009(E)
5.6 Maximum power
The maximum power of the active reflector shall not exceed 10 W.
5.7 Tolerance to a radar in close proximity
2
The reflector must be able to withstand a continuous pulse power density of 2 kW/m . This is equivalent to a
1)
25 kW radar, 1 µs, with a 1,83 m antenna at a range of 30 m.
6 Environmental requirements
The active radar reflector shall meet the dry heat, damp heat, low temperature, solar radiation, vibration, rain
and spray and corrosion requirements of IEC 60945 where they are applicable. If the design of the active
radar reflector system is such that some parts are intended to be installed in an exposed position and others
in a protected position, then the tests to which each part shall be subjected shall be those which apply to the
intended position.
7 Inspection and type tests
7.1 Inspection
A visual inspection shall be carried out to confirm that the construction and finish of the reflector is such that
the unit is safe to handle. For example, burrs should be removed and, if applicable, wires fixed so that injury
cannot occur during the handling of the reflector.
7.2 Testing
Tests will normally be carried out at test sites accepted by the type test authority for these tests. General
requirements for the competence of testing and calibration laboratories are given in ISO 17025.
The manufacturer shall, unless otherwise agreed, set up the equipment and ensure that it is installed in
accordance with their installation requirements before type testing commences.
7.3 Performance tests
7.3.1 General
The reflective performance tests shall be conducted in a free-field environment where the background noise
2
level has been reduced to the equivalent echoing area of 0,01 m or less at frequencies between 2,900 GHz
to 3,100 GHz and 9,300 GHz to 9,500 GHz. Typically, a fully anechoic microwave test chamber, specified for
up to 10 GHz operation, would be used for the conduct of these tests. Before use, the reflector test range shall
be calibrated using a precision sphere of known radar cross section. These tests may be carried out using a
continuous wave (CW) or pulsed signal. CW signals are atypical of current magnetron radar but produce lower
uncertainties in reflector testing. Due to the 100 % duty cycle of a non-fluctuating CW signal, the manufacturer
should be consulted to ascertain the maximum time tests can be conducted and the duration of any rest
period to allow for equipment under test (EUT) cooling. The tests should be carried out at both X band
(9,410 GHz) and S band (3,050 GHz) with the same power density at the EUT turntable that was used for the
chamber calibration. This power density should be at least 6 dB below the level required to saturate the EUT,
unless otherwise stated in the test clause. For illustration, an instrumentation schematic is given in Figure 3.
1) 1,83 m ≈ 6 ft.
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ISO 8729-2:2009(E)
Key
1 fully anechoic chamber
2 equipment under test
3 receive antenna
4 transmit antenna
5 positioner (azimuth/elevation)
6 radar absorbent material
7 directional coupler
8 vector network analyser
9 position controller
10 PC
Figure 3 — Instrumentation schematic
7.3.2 SPL measurement
7.3.2.1 General
The test shall consist of a series of measurements to produce azimuthal polar diagrams of the reflector
performance within the volume 360° azimuth and the required angle (±) of heel (see 5.2.2). Measurements
shall be taken using a turntable capable of moving the EUT at intervals u 1° in azimuth and u 0,5° in elevation.
The arrangement of the turntable shall give azimuth movement over elevation. Azimuthal polar diagrams shall
be produced at 5° vertical intervals up to 10° or 20° depending on the designation of the EUT (see 5.2.2) both
towards and away from the interrogating signal source. The turntable shall rotate at an angular speed to
match instrumentation data capture rate, and measurement data should be recorded to a computer
spreadsheet so that the SPL, which has a dynamic relationship with the 280° requirement and nulls, can be
calculated for each plot.
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ISO 8729-2:2009(E)
7.3.2.2 SPL designation
Following the analysis of the azimuthal polar diagrams from the measurements of 7.3.2.1, the lowest SPL
calculated shall be designated as the SPL for that particular radar reflector with respect to its declaration of
use (see 5.2.1).
7.3.3 Time delay test
The EUT shall be placed in its normal mounting attitude in the anechoic chamber and the instrumentation set
up to investigate the returned signal in the time/frequency domain. An instrumentation schematic is given in
Figure 3. The EUT shall be rotated such that the maximum RCS position is aligned with the test antennas. For
effective measurement of the EUT’s stability and inherent time delay, swept frequency measurements will be
made with a bandwidth of 200 MHz. This frequency domain data will be Fourier transformed into the time
domain to give an RCS result plotted against time. Measurements will be made with the device switched off
(to give a time reference) and with the device switched on. Typical results are given in Figures 4 and 5. The
time delay can be seen as the time difference between the passive return from the EUT and the first active
(main) return. Initial returned signals may be affected by any power management arrangements such as the
use of a “wake up” trigger, and appropriate test allowance may be made.
Key
2
R radar cross section, expressed in dBm
t time, expressed in ns
1 reflection from body of equipment under test
Figure 4 — RCS plotted against time (device switched off)
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ISO 8729-2:2009(E)
Key
2
R radar cross section, expressed in dBm
t time, expressed in ns
1 reflection from body of equipment under test
2 main return
3 coupled returns from equipment under test decreasing
Figure 5 — RCS plotted against time (device switched on, not in saturation)
7.3.4 Stability test
The time delay test shall be repeated and the power of the excitation signal increased until the main return
reaches its maximum (saturates). If the coupled returns decrease (as shown in Figure 5), then the device is
completely stable. If the returns increase with time until saturation is reached (when their level remains
constant, as shown in Figure 6), then the device is unstable.
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ISO 8729-2:2009(E)
Key
2
R radar cross section, expressed in dBm
t time, expressed in ns
1 reflection from body of equipment under test
2 main return
3 coupled returns from equipment under test increasing
4 coupled returns from equipment under test in saturation
Figure 6 — RCS plotted against time (device switched on, in saturation)
7.3.5 Induced instability test
2 2
The above test shall be repeated but with a corner reflector of RCS 10 m for an X band test and ≈1 m for
S band, placed 3 m from the EUT. The corner reflector, shall be placed such that it is out of the normal test
signal path and oriented so as to return the maximum signal to the active device. The EUT shall be rotated
such that its maximum RCS position is aligned with the corner reflector, and the power of the interrogating
signal shall be gradually increased to a level at which the EUT saturates. Figure 7 shows that when the corner
reflector is introduced, a separate reflection 20 ns behind the main reflection is created. If the secondary
returns decrease with time, as Figure 7 shows, then instability has not been induced.
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ISO 8729-2:2009(E)
Key
2
R radar cross section, expressed in dBm
t time, expressed in ns
1 reflection from body of equipment under test
2 main return
3 coupled returns from equipment under test decreasing
4 coupled returns from corner reflector decreasing
Figure 7 — RCS plotted against time (device switched on, not in saturation, with corner reflector)
7.3.6 Power emission test
The aim of this test is to confirm that the power output of the active radar reflector is sufficient to create a
return which will be detected by the interrogating radar.
This test shall be conducted with the power density of the simulated radar signal, calculated for a range of five
2)
nautical miles [9 260 m ], at the turntable as given in Table 1.
Table 1 — Power density required at the turntable
a
Frequency Peak power density required
2
(GHz) (W/m )
3,050 0,011
9,410 0,023
a
This power density has been calculated using 25 kW and 30 dBi for a
typical X band radar and 30 kW and 26 dBi for a typical S band radar.
2) 1 nautical mile = 1 852 m (exactly).
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ISO 8729-2:2009(E)
If the EUT is saturated at these powers, then the power shall be reduced until the EUT is out of saturation.
The azimuthal polar diagram shall be produced and the SPL calculated as specified in 7.3.2.1 for 0° heel.
2 2
The SPL shall have minimum values of 7,5 m or 0,5 m , depending on the frequency.
7.3.7 Saturation power test
Power shall be applied to the input to the amplifier without antennas and increased until the amplifier is in a
saturated condition. The output power shall then be measured. This output power shall be adjusted by the
gain of the transmit antenna, and it shall be confirmed that the result is less than 10 W.
7.3.8 Tolerance to a radar in close proximity check
The manufacturer shall provide documentary evidence that the reflector can withstand the power density
defined in 5.7.
7.3.9 Pulse length check
The interrogating signal, having a pulse length of 0,5 µs and interrogation interval of 1 000 Hz at levels
saturating the active radar reflector, shall be emitted at frequencies of both 9,410 GHz and 3,050 GHz to
detect the returned signal. It shall be confirmed that the pulse length of the returned signal differs by no more
than 10 % (or 10 ns, whichever is greater) of the interrogating signal.
If acceptable to the approving authority, this confirmation may be demonstrated by theory.
7.4 Environmental tests
7.4.1 The reflector shall meet the requirements of the following tests specified in IEC 60945:
⎯ dry heat test;
⎯ damp heat test;
⎯ low temperature test;
⎯ vibration test;
⎯ solar radiation test;
⎯ rain and spray test (exposed items only);
⎯ corrosion test.
If the design of the active radar reflector system is such that some parts are intended to be installed in an
exposed position and others in a protected position, then the tests to which each part shall be subjected shall
be those which apply to the intended position.
7.4.2 IEC 60945 requires performance tests or checks to be carried out during the test programme. Since a
performance test needs specialised equipment used in a free-field environment for qualitative results, the
“performance check” shall consist of a visual examination during the tests for any damage visible to normal
eyesight. The reflector shall be supplied with its normal power during the tests and the current monitored. Any
significant increase in current in the absence of a radar excitation signal would indicate a failure due to self
oscillation. The performance test shall consist of the full reflective performance tests from 7.3.1 to 7.3.2.1
conducted on the sample reflector after completion of the environmental tests given in 7.4.1.
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ISO 8729-2:2009(E)
7.5 Mechanical strength test
The reflector shall be mounted in the recommended way and moved under water at a relative velocity of
1,3 m/s in both directions in each of the mutually perpendicular planes consecutively.
7.6 Elec
...
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