NDF of the near-field of a strip source in orthogonal directions
In the manuscript, we address the problem of evaluating the
number of degrees of freedom (NDF) of the field radiated by a strip source along all the directions orthogonal to it.
The NDF represents at the same time the number of independent functions required to represent the data with a given degree of accuracy, and the dimension of the unknowns subspace that can be stably reconstructed. For such reason, the knowledge of the NDF gives insight on the forward and on the inverse problems and it represents one of the metrics to evaluate the achievable performance in the inversion.
The main difficulty arises since in near-zone the eigenvalue
problem that must be solved for the computation of the NDF,
involves a non-convolution and non-bandlimited kernel. In the paper, we show how to overcome this drawback and how to obtain a closed-form expression of the NDF which highlights the role played by the configuration parameters.