Amplitude monopulse direction finding refers to a common technique employed in radar systems to improve the accuracy with which the direction of arrival of a pulse can be estimated.
Two overlapping antenna beams are formed, which are steered in slightly different directions, usually such that they overlap at the 3dB-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 (SNR). An accuracy of a tenth of beamwidth can be achieved with an SNR of 10dB.
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.
Two beams, steered so that they overlap
Sum of the two beam patterns
Difference of the two beam patterns
Ratio of the sum-difference patterns