Simple filter with limited rotation invariance

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Abstract
A new filter with limited rotation invariance for real target functions is proposed. The filter is the Fourier transform of the real part of a circular harmonic component of a target. The range of limited rotation invariance depends on the harmonic order. The lower the order, the wider the range. An expression for the peak correlation intensity at the origin of the correlation plane is derived. A computer experiment confirms the theoretical predictions. The optical experiment shows the ability of the filter to recognize a target within an angular range of 40° in the presence of other patterns.