Amplitude-comparison monopulse refers to a common
direction finding
Direction finding (DF), radio direction finding (RDF), or radiogoniometry is the use of radio waves to determine the direction to a radio source. The source may be a cooperating radio transmitter or may be an inadvertent source, a naturall ...
technique. This method is used in
monopulse radar
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 prob ...
,
electronic warfare and
radio astronomy
Radio astronomy is a subfield of astronomy that studies Astronomical object, celestial objects using radio waves. It started in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation coming from the Milky Way. Subsequent observat ...
. Amplitude monopulse antennas are usually
reflector antennas.
Approach
Two overlapping antenna beams are formed, which are steered in slightly different directions, usually such that they overlap at the
half-power point (-3 dB-point) of the beams. By comparing the relative amplitude of the pulse in the two beams, its position in the beams can be determined with an accuracy dependent on the
signal-to-noise ratio
Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in deci ...
(SNR). An accuracy of a tenth of beamwidth can be achieved with an SNR of 10 dB.
In most implementations, two signals are formed, one being the sum of the two beams, and the other being the difference of the two beams. The ratio of these two beams normalises the difference signal and allows the direction of arrival of the signal to be calculated. The shape of the antenna beams must be known exactly and hence the accuracy of the techniques can be affected by unwanted multipath reflections.
Amplitude-Comparison Monopulse
- Tracking Radar, Chap 18, p. 9
Image:MonopulseBeams.gif, Two beams, steered so that they overlap
Image:MonopulseSum.gif, Sum of the two beam patterns
Image:MonopulseDiff.gif, Difference of the two beam patterns
Image:MonopulseRatio.gif, Ratio of the sum-difference patterns
See also
* Monopulse radar
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 prob ...
* Phase-Comparison Monopulse
References
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Radar signal processing