Planar Near-Field Antenna Measurements with a Uniform Step Larger than Half-Wavelength

In this paper, a new sampling scheme of the near field radiated by a planar source is proposed and assessed. More in detail, the paper shows a uniform sampling criterion that allows representing the near field over a plane with a number of measurements lower than the classical half-wavelength sampling. At first, a discretization strategy of the near field based on the warping method is recalled from the literature. In the region of the observation domain located in front of the source, the warping sampling scheme employs a non-redundant number of measurements since it predicts the exact positions where the near-field samples must be collected. On the contrary, in the region of the measurement plane beyond the source, it does not return the exact positions of the field samples. For such reason, a spatially varying oversampling can be used to avoid loss of information in the discretization process and to maintain the number of field samples as low as possible. Despite the warping method represents the state of the art in terms of number of measurements, it requires acquiring the near field samples over a non-uniform grid. To overcome this drawback, in this paper, the spatially varying oversampling is chosen in such a way that the resulting sampling becomes uniform. Such choice still ensures a growth of the sampling rate only at the edges of the observation domain permitting the retrieval of the near field by its samples with fewer measurements than the half-wavelength sampling. Finally, numerical simulations based on synthetic and experimental data corroborate the effectiveness of the approach in recovering both the near and the far field.