False detections in Klein Heidelberg

The first modern bistatic radar system, Klein Heidelberg (KH), was developed by the Germans during World War II to exploit the transmissions from the British Chain Home (CH) radars and achieved detection ranges against Allied bombers well behind CH. The small backlobe of the system would also have unavoidably detected German aircraft flying behind KH. After estimating the front-back ratio of the antenna, the detection ranges of these German aircraft were derived, showing that they would have been detected out many tens of kilometres and have been incorrectly plotted as Allied aircraft flying well over South East England. While this study is essentially historical in nature, it is based on data in intelligence reports that were declassified only recently and illustrates the need for designers of such systems to anticipate all unwanted modes of operation.