donutsignaal

Donutsignaal is a term used in signal processing and imaging to describe signals whose energy in the frequency domain forms a ring around the origin, often illustrated as a donut-shaped spectrum. Unlike a typical low-pass signal that concentrates energy near zero frequency, a donutsignaal concentrates energy on a circle with a nonzero radius, effectively suppressing low frequencies. The term is mainly used in Dutch-language literature and may refer to either the two-dimensional Fourier transform of a spatial signal or to radial band-pass characteristics in other domains.

A donutsignaal can be constructed by applying a circular band-pass filter with defined inner and outer radii in the frequency domain, or by modulating a base signal with a circularly symmetric kernel. In optics or wave physics, such spectral shapes arise naturally from circular apertures, phase vortices, or orbital-angular-momentum beams, producing donut-shaped intensity patterns in the spatial domain.

Applications include imaging and beam shaping, where a donut-like spectrum can improve edge preservation or suppress speckle, as well as radar and sonar signal processing where radial bandwidth supports angular resolution or resolution at a particular scale. In practice, the concept is closely related to ring filters, cylindrical harmonics, and Laguerre-Gauss beam theory.

Donutsignaal as a term is not universally standardized and may be used loosely to describe any ring-shaped spectral content. When used, it is important to specify the dimensionality (1D vs 2D), the radii of the ring, and the exact spectral window.