How to choose a Radar Reflector

This article looks at the results of an independent study commissioned by the Marine Accident Investigations Branch (MAIB) to help leisure boat owners choose the most appropriate radar reflector for their vessel from those currently on the market.

Ship in FogThe study tested and compared a selection of radar reflector types in terms of their free space Radar Cross Section (RCS) performance, giving yachtsmen, fishermen and small boat owners the knowledge to make an informed judgement about the type and size of reflector they should fit in order to have the best chance of being detected on the radar of larger ships.

Which Should you Choose?

Here is a summary comparison of the different types of radar reflector following the testing.

 
ReflectorDimensionsWeightPrice (Approx)
Plastimo 16" Octahedral Folding300 x 300 415mm0.65kg16
Plastimo 4" Tube Type590 x 100mm0.9kg40
Davis Echomaster Folding320 x 320mm 60
Tri-Lens Large160 x 160 x 80mm5.5kg300
Tri-Lens Standard120 x 120 x 60mm2.5kg130
Echomax EM230610 x 248mm2.4kg130
Firdell Blipper 210-7595 x 240mm1.8kg130
Sea Mea Active RTE416 x 50mm0.4kg500
POLARef (Test Unit)279 x 279mm5kg2000

- The Sea-Me is a good example of an active reflector (RTE) exceeding the requirements of the current and future ISO 8729 at heel or elevation angles of up to 15˚. It is also very small and light. Drawbacks are that it requires power to operate (which on a yacht is often at a premium) and it will only operate at X-Band and will offer no performance at S-Band.

- The POLARef shows excellence is possible but at a price. Technically it just failed meet current ISO 8729 standards or its replacement ISO 8729. The main drawbacks are that it is very costly at 2,000 and it is quite heavy, at around 5kg. It is currently only used as a radar measurement standard, although it could possibly be re-engineered for commercial production which could reduce the price.

- The Large Tri-Lens performed well particularly at larger angles of heel and elevation. It just fell short of the ISO 8729 standard having a peak RCS of 8.5m2, but otherwise it performed well. It is the heaviest reflector supplied for test at 5.5kg and costs around 300.

- The particular Echomax EM230 unit in this test narrowly failed to meet the ISO 8729 standard in testing, although it must be noted that in previous independant studies carried out at the same Qinetiq test facility the EM230 fully met the ISO 8729 standards and has received SOLAS Ships Wheel Type Approval. It showed good peak and average RCS performance. The reflector is reasonably priced at 130 and weighs 2.4kg. Its main drawback was a RCS drop-off above an elevation angle of 10˚.

- The Firdell Blipper 210-7 also failed to meet the ISO 8729 standard during this testing, but showed good peak and average RCS performance. The Blipper is priced at 130 and weighs 1.8kg. Its main drawback was a RCS drop-off above an elevation angle of 10˚.

- The Standard Tri Lens does not meet the ISO 8729 standard as the peak RCS was too low at 4m2. However, its consistent RCS response outperformed most of the other reflectors when heeled beyond 10˚. It is reasonably priced at 130 and weighs 2.5kg.

- The Plastimo 16" octahedral is inexpensive at 16 and lightweight at 0.65kg but failed to meet the ISO 8729 standard in either of the positions tested. It had reasonable peak and average performance averaging around 2m2 but had wide nulls which kept its stated performance level down. Other drawbacks are that its mounting arrangement is by suspension only (often in an unfavourable position) and could be subject to damage.

- The Davis Echomaster failed to get close to the ISO 8729 standard during this testing. Its peak RCS was too low at 7.5m2 and its average performance was only 1.75m2. This reflector is priced at 60 and is lightweight. It can also be mounted on a rod as well as by suspension (in the correct catch-rain position).

- The 4" Plastimo Tube Type reflector performed poorly.

Ship at Close QuartersReaders could conclude from this independent study that the active Sea-Me RTE, and the Standard or Large Tri-Lens radar reflectors offer the best performance at heel and elevation angles of over 10˚.

Some Useful Advice from MAIB

- Based on the results of this study, it is recommended that yachtsmen always fit a radar reflector that offers the largest RCS practicable for their vessel.

- The RCS of the radar reflector should have a minimum consistent RCS of 2m2.

- The Sea-Me Actice Radar Target Enhancer is the recommended product if power is available. If power is not available, then the passive Large Tri-Lens reflector is recommended

- A 4" tube reflector is not considered suitable due to its poor performance. It is also recommended that the 2" tube reflector is unsuitable as the performance of this target will be even lower.

- We strongly recommend that poorly performing radar reflectors are not fitted as you could be lulled into a false sense of security, believing that your chances of detection has been enhanced, when in fact the opposite is the case.

The Test Results

The Sea-Me Active Radar Target Enhancer had a peak RCS that is very high in comparison to the passive reflectors described in the report. On the basis of these results, it is the only reflector tested that would fully satisfy the performance requirements of ISO 8729-1 and the
proposed specification for ISO 8729-2 (only up to an elevation angle of 10˚ or
Category 1).

The POLARef reflector narrowly failed the current and future ISO 8729 specifications although its performance was exceptionally good, having a very consistent RCS over the other elevation angles tested.

The Large Tri-Lens radar reflector performed consistently over all the elevation angles tested with very little variation in its peak and average RCS.

The Echomax EM230 demonstrated good peak and average RCS performance compared
to the other products but its stated performance level drops significantly beyond an
elevation angle of 5˚. The Echomax 230 tested failed to meet the total angle >0.625m2
aspect of ISO 8729.

The Firdell Blipper 210-7 peak RCS figures were good but the average and stated performance levels reduced when the reflector went past an elevation angle of 5˚. The Firdell Blipper 210-7 tested failed to meet the total angle >0.625m2 aspect of ISO 8729 at -10 and 15˚ elevation

The Standard Tri Lens performed similarly to the Large Tri-Lens although the peak RCS was low at about 3.75m2. It was very consistent up to an elevation angle of 20˚ with the average RCS only varying by 0.07m2.

The Plastimo 16" octahedral had a good peak and average performance when mounted in its upright position although the large nulls shown in its azimuth patterns bring the stated performance level down. In the catch-rain position, the reflector was more consistent although it had a lower peak RCS. It failed to meet ISO 8729 in both orientations due to its null widths at 0˚ and the total angle >0.625m2.

The Davis Echomaster had a reasonable peak and average RCS but was too small to meet the performance requirements of ISO 8729.

The 4" Tube reflector had a good peak RCS of 9.3m2 at 0˚. However, as the elevation angle increased, the RCS rapidly decreased. Even at 1˚ the stated performance level had dropped to 0.12m2.

For a copy of the full Radar Reflectors Report published by MAIB see:
MAIB 'Performance Investigation of Marine Radar Reflectors on the Market'

For the full range of Radar Reflector products from Safety Marine see: Radar Reflectors

 

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