The Lexus-sourced illustration, left, appeared on page 43 of the special 110th anniversary edition of Autocar (click the pic for a bigger version). It illustrates the radar controlled Pre-Crash Safety System fitted to the new Lexus IS220d.

It does make one wonder where Lexus gets its radar components. Plenty of military boffins would dearly love to get their hands on a radar with a perfectly rectangular beam cross-section.

In reality, radar beams are a lot less neat and tidy. They are lumpy things. They might have a strong main beam of oval cross-section but will also have a number of lesser side beams pointing up, down and to the sides of the main beam.

These so-called sidelobes have the potential to create false reflections that can confuse the system – this appears to be the problem faced by Mercedes in its recent embarrassing TV incident, given that technicians blamed the fabric of the building surrounding the ill-fated Merc, even though the way ahead was clear for the main beam to penetrate the fog.

Talking of fog, millimetre wavelength radar works well in fog, mist, dusty conditions and in ordinary rain, but works a lot less well in very heavy rain made up of large droplets. Presumably makers of cars equipped with radar-based systems warn owners that they should put less faith in the system when it’s really hammering down?

Well, given the misleading nature of the Lexus picture, probably they don’t.

Perhaps radar assistance systems ought to be deactivated when the wipers are on their maximum setting...