Target Pattern Maps — A Description & Explanation

It is useful to provide a visual representation of a radar detection reflector’s basic RCS  (Radar Cross Section) performance. The method used in the infancy of radar was a polar diagram. This is perfectly acceptable for simple static single operation. However, a polar diagram is useless for describing the performance of a radar detection reflector because it is a dynamic system. Polar diagrams are specific to a tiny part of the operating envelope. This became a major problem for the defence industry, where the radar signature performance of a weapons platform is a matter of life and death. Any attempt to understand thousands of polar diagrams relating to simple objects moving around at sea or in the air was nearly impossible.

Clearly something better had to be found. Fortunately somebody realised that all of these thousands of polar diagrams could be represented as a Target pattern map (TPM). This format has been used by the defence industry for decades to describe the performance of dynamic targets like detection reflectors. There really is no mystery in TPMs. They are made up of a large number of polar diagrams that have been unwrapped so that they form a linear shape like a saw blade. The saw blades are then tipped onto its edge and stacked together. The saw teeth now form peaks and valleys. The TPM is simply a contour map of the peaks and valleys of many straightened- out polar diagrams. To generate a meaningful TPM requires a large amount of data. This data has to be derived from very accurate physical testing at very fine increments of rotation and heel.

The TPM is an immensely powerful analytical tool allowing an immediate insight into the radar performance of any object of interest. It is the professional visual representation method for radar signature within the radar imaging industry. There, however, appears to be a reluctance to adopt TPMs by some manufactures of radar reflectors. This is unfortunate, as in Firdell’s view it casts a shadow on the professionalism of our industry. Firdell earnestly believes that TPM’s provide crucial information for customers as they clearly show a reflector's performance and demonstrate that the reflector has been very carefully tested.

The TPM will clearly show if the fundamental characteristic of a good detection reflector is present. A TPM of a good radar detection reflector will show a uniform distribution of many peaks and valleys with all of the peaks at similar magnitude. Some manufactures claims peaks of large value for their products. This is misleading as, although they may be large, the peaks may be isolated, (and thereby tend to create the intermittent effect described above). The ideal detectable performance requires many peaks with a value over the threshold of detection. The Target Pattern Map will show all of the peaks and their distribution. It can therefore be seen that many peaks are much better than a few large ones.

Providers of mediocre or poor performing devices can hide behind a single point Polar Diagram and pretend that it represents performance over the whole operating envelope. The claim of large maximum RCS values is also meaningless as without a TPM it is impossible for a customer to tell if this is a 1-degree spike or a consistent value over the total operating range. A Target Pattern Map is the clearest way of comparing the performance of different products, and Firdell believes they are essential to enable users of detection reflectors to make an informed choice.
















Firdell Radar Reflectors Ltd. - Shirebrook House - Buxhall - Stowmarket - Suffolk - IP14 3DQ - United Kingdom