Validity of the Parabolic Wavefront Model for Near-Field MIMO

Motivated by the widespread adoption of the parabolic wavefront model for the analysis and characterization of near-field multiple-input multiple-output (MIMO) communication and positioning, this paper presents an extensive analysis of this model's validity. Insightful relationships are derived for the combinations of transmission range, wavelength, and array apertures that ensure that the model is valid to within some desired accuracy. Furthermore, a connection is drawn with the number of spatial degrees of freedom that the model can fundamentally represent.