Abstract
We investigated near-field effects on free-space ranging with ultra-wideband millimeter-wave (mmWave) radar. In this application, one often assumes far-field conditions. However, with increasing requirements of accuracy, far-field assumptions are not satisfying. The radar measurements are affected by phase variations, leading to erroneous distance estimates. To simulate and approximate these effects, we propose computational methods by means of physical optics. They were validated using a state-of-the-art frequency-modulated continuous-wave radar sensor. Sophisticated experiments show good agreement; thus, in practice, the methods can be used to correct distance estimates to achieve micron accuracy without extensive calibration in advance.
Highlights
R ANGE measurement with mono-static radar refers to measuring the distance between the reference points of the antenna and the radar target
One often assumes far-field conditions, i.e., point sources of radiation, point scatterer, and planar wavefronts; the reference points are described by the concept of antenna phase center [1]–[7] and the scattering center of the radar target [8]–[10]
More precisely: only with increasing distance of observation, the equiphase surfaces of curved wavefronts become concentric spheres originating at the antenna phase center and the target scattering center, respectively
Summary
R ANGE measurement (ranging) with mono-static radar refers to measuring the distance between the reference points of the antenna and the radar target. One often assumes far-field conditions, i.e., point sources of radiation, point scatterer, and planar wavefronts; the reference points are described by the concept of antenna phase center [1]–[7] and the scattering center of the radar target [8]–[10]. More precisely: only with increasing distance of observation, the equiphase surfaces of curved wavefronts become concentric spheres originating at the antenna phase center and the target scattering center, respectively This leads us to the definition of the near-field variation of reference points as the deviation of the actual position of reference points in radar measurements – which are not related to any physical point in space – from the far-field centers of the antenna and the target. THEORY OF NEAR-FIELD PHASE VARIATIONS Fig. 1 depicts the geometry of the investigated problem, where S1 and S2 are planar surfaces bounding the antenna aperture and the target cross-section, respectively.
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