Method and arrangement for determining the spatial frequency of a signal

1. A method for determining the spatial frequency of a signal in a given plane intersected by said signal, said plane including a plurality of sensors arranged in arrays, the method comprising the steps of:

sampling said signal with a first sensor array, the distance between adjacent sensors defining a first spatial sampling frequency, the first spatial sampling frequency being lower than the spatial frequency of the signal;

sampling said signal with a second sensor array, the distance between adjacent sensors defining a second spatial sampling frequency lower than said first spatial sampling frequency, said first and second sensor arrays being interleaved;

identifying a signal pair of corresponding signals of the signal sampled with the first sensor array with the signal sampled with the second sensor array, the signal pair being identified by detecting a high correlation factor between the corresponding signals;

identifying a relative difference between the first spatial sampling frequency and the second spatial sampling frequency;

determining a first spatial frequency shift factor based on the first spatial sampling frequency and the relative difference between the first spatial sampling frequency and the second spatial sampling frequency; and,

up-converting the signal sampled with the first sensor array using the first spatial frequency shift factor to obtain the spatial frequency of said signal.

2. The method according to claim 1 , further comprising the steps of:

determining a second spatial frequency shift factor based on the second spatial sampling frequency and the relative difference between the first spatial sampling frequency and the second spatial sampling frequency;

up-converting the signal sampled with the second sensor array using the second spatial frequency shift factor and,

adding the up-converted signal sampled with the first sensor array to the up-converted signal sampled with the second sensor array.

3. The method according to claim 1 , further comprising the step of retaining signals with a high correlation figure and muting signals with a lower correlation figure.

4. The method according to claim 1 , further comprising the step of filtering said signal with an anti-aliasing filter before it is sampled, said anti-aliasing filter having a cut-off frequency equal to the multiple of said first and second spatial sampling frequencies.

5. The method according to claim 1 , further comprising the step of determining a direction to a source emitting a signal, by determining the spatial frequency of said signal received by first and a second interleaved sensor arrays in a plane containing said sensors arrays and comparing the spatial frequency with an instantaneous frequency of the signal.

6. The method according to claim 1 further comprising the step of determining a direction to a source emitting a signal, the sensors in said first array being arranged in rows and columns defining a first matrix,

wherein the sensors in said second array are arranged in rows and columns defining a second matrix,

by determining the spatial frequency of the signal detected in a row, comparing said spatial frequency with an instantaneous frequency of said signal and determining an azimuth angle for the incoming signal,

by determining the spatial frequency of the signal detected in a column, comparing said spatial frequency with the instantaneous frequency of said signal and determining an elevation angle for the incoming signal.

7. The method according to claim 1 , wherein the steps of sampling said signal with a first sensor array and sampling said signal with a second sensor array are simultaneously and separately processed.