returned signal. Since conical scanning systems depend on the signal growing or weakening due only to the position of the target relative to the beam, such changes in reflected signal can cause it to be "confused" about the position of the target within the beam's scanning area. Jamming a conical scanner is also relatively easy. The jammer simply has to send out signals on the radar's frequency with enough strength to make it think that was the strongest return. In this case, a series of random short bursts of the signal will appear to be a series of targets in different locations within the beam. Jamming of this sort can be made more effective by timing the signals to be the same as the rotational speed of the feed, but broadcast at a slight delay, which results in a second strong peak within the beam, with nothing to distinguish the two. Jammers of this sort were deployed quite early. The British used them during World War II against the German conical-scanning Würzburg radar. Description Monopulse basics Monopulse radars are similar in general construction to conical scanning systems, but split the beam into parts and then send the two resulting signals out of the antenna in slightly different directions. When the reflected signals are received they are amplified separately and compared to each other, indicating which direction has a stronger return, and thus the general direction of the target relative to the boresight. Since this comparison is carried out during one pulse, which is typically a few microseconds, changes in target position or heading will have no effect on the comparison. Making such a comparison requires that different parts of the beam be distinguished from each other. Normally this is achieved by splitting the pulse into two parts and polarizing each one separately before sending it to a set of slightly off-axis feed horns. This results in a set of lobes, usually two, overlapping on the boresight. These lobes are then rotated as in a normal conical scanner. On reception the signals are separated again, and then one signal is inverted in power and the two are then summed ( in the image). If the target is to one side of the boresight the resulting sum will be positive, if it's on the other, negative. If the lobes are closely spaced, this signal can produce a high degree of pointing accuracy