ISO 8729-2:2009. In 1995 the International Maritime Organisation (IMO), decided that the performance characteristics called up in ISO 8729:1999 were not sufficiently stringent to give sailors using reflectors, even if it met them, an acceptable chance (taken as 80%) of being detected by radar. IMO issued a performance specification which was the basis of the new standard ISO 8729-2:2009. It's performance demands are, rightly, considerably tougher than those of the 1999 version. Because all vessels over 3000 tons must carry both S and X Band radars ISO 8729-2:2009 also introduced the requirement that reflectors must respond at both X and S Bands.
The performance requirement today is expressed in terms of the Stated Performance Level (SPL) which, for an RTE, is the Radar Cross Section achieved over 280° out of the full 360°.
For X Band the SPL must be at least 7.5 sq m and for S Band 0.5 sq m. These levels must be achieved at 20° heel for monohull sailing vessels. It is unlikely that a passive reflector of a size and weight suitable for the average sailing yacht will be able to achieve the level of performance now required.