The visualization you see is an attempt to represent a four-dimensional concept in a 3D space. The signal is a complex exponential:

\[s(t) = e^{j\theta(t)} = \cos(\theta(t)) + j\sin(\theta(t))\]

Here, the phase θ(t) is not linear. Its derivative, the instantaneous frequency, increases over time. This is called a “chirp” signal.

The Axes

  • Real Axis (X): Represents the real part, cos(θ(t)).
  • Imaginary Axis (Y): Represents the imaginary part, sin(θ(t)).
  • Frequency Axis (Z): This axis is used to represent the passage of time, during which the frequency increases, causing the spiral to tighten.

This creates the distinctive “chirping” spiral you see.