Amplitude-Comparison Monopulse

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.

Approach

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

Signal-to-noise ratio

Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...

 (SNR). An often used rule of thumb

Rule of thumb

A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination...

is that 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.