page_title: Monopulse radar
section_title: Monopulse basics
hierarchical_section_title: Monopulse radar / Description / Monopulse basics
caption_attribution_description: Français&#160;: Principe du système monopulse
context_page_description: Monopulse radar is a radar system that uses additional encoding of the radio signal to provide accurate directional information. The name refers to its ability to extract range and direction from a single signal pulse.
  Monopulse radar avoids problems seen in conical scanning radar systems, which can be confused by rapid changes in signal strength. The system also makes jamming more difficult. Most radars designed since the 1960s are monopulse systems. The monopulse method is also used in passive systems, such as electronic support measures and radio astronomy. Monopulse radar systems can be constructed with reflector antennas, lens antennas or array antennas.
  Historically, monopulse systems have been classified as either phase-comparison monopulse or amplitude monopulse. This is because some common implementions have been based on a phase comparison or an amplitude comparison. Modern systems determine the direction from the monopulse ratio, which contain both amplitude and phase information. The monopulse method does not require that the measured signals are pulsed. The alternative name "simultaneous lobing" has therefore been suggested, but not popularized.
context_section_description: 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 within the beam, adding to the natural accuracy of the conical scanning system. Whereas classical conical scan systems generate pointing accuracy on the order of 0.1 degree, monopulse radars generally improve this by a factor of 10, and advanced tracking radars like the AN/FPS-16 are accurate to 0.006 degrees. This is an accuracy of about 10 m at a distance of 100 km.
  Jamming resistance is greatly improved over conical scanning. Filters can be inserted to remove any signal that is either unpolarized, or polarized only in one direction. In order to confuse such a system, the jamming signal would have to duplicate the polarization of the signal as well as the timing, but since the aircraft receives only one lobe, determining the precise polarization of the signal is difficult. Against monopulse systems, ECM has generally resorted to broadcasting white noise to simply blind the radar, instead of attempting to produce false localized returns.
caption: Monopulse beam of a phased array antenna split in two lobes.
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