Fast and Accurate Antenna Pattern Evaluation From Near-Field Data Acquired via Planar Spiral Scanning

Reconstruction of the Far-Field Pattern of Volumetric AUTs from a Reduced Set of Near-Field Samples Collected along a Planar Spiral with a Uniform Step

“…Therefore, the probe should co-rotate in order to maintain its axes parallel to those of the AUT. The usage of a first-order probe enables a “soft” co-rotation [ 31 ], allowing us to relate the no co-rotated voltages and to the corresponding co-rotated ones and through the relations: …”

“…NTFFT techniques with planar spiral scanning have been developed in [ 27 , 28 , 29 , 30 , 31 , 32 , 33 ] by suitably following such a hint. In particular, the NTFFTs in [ 28 , 29 , 30 , 31 , 32 , 33 ] permit a greater saving time, since, by applying the non-redundant representations [ 24 , 25 ] and properly exploiting the unified theories of spiral scans [ 32 , 33 ], they employ a reduced number of NF samples and spiral turns. Two-dimensional (2-D) optimal sampling interpolation (OSI) expansions allow one to accurately recover the huge number of NF data required by the standard plane-rectangular NTFFT [ 9 ] from the non-redundant spiral samples.…”

“…The remarkable saving of measurement time is due to both the hugely reduced number of required NF samples and to how the rotary movement of the AUT positioner and the linear one of the probe positioner are combined during the acquisition on fly. In any case, such a drastic measurement time saving is obtained at the expense of a non-uniform step of the spiral [ 28 , 29 , 30 , 31 ]. In fact, since the spiral step is related to the sample spacing needed for the interpolation on a radial line, the distance between two consecutive intersections of the spiral with a radial line grows on increasing the distance from the center of the scanning area.…”

Laboratory testing of an SVD‐based approach to recover the non‐redundant bi‐polar NF data from the positioning error affected ones

“…The OSI scheme, obtained by matching the expansions (6) and (13), can be applied to efficiently reconstruct V α and V δ at the points required by the PR NFTFF transformation [6]. However, the formulae in [6] (whose expressions in the employed reference system are reported in [9,29]) are valid when the probe and AUT axes are kept parallel and this requires the co-rotation of the probe with the AUT. In any case, by using a probe, which exhibits only a first-order φ-dependence in its FF, as, for instance, an open-ended rectangular waveguide fed by a TE 10 mode [30], the voltages V y and V x , which would be measured when co-rotating the probe and rotated probe, can be obtained from the V α and V δ ones by using the relations…”

Laboratory tests on an near‐field to far‐field transformation technique from non‐redundant bi‐polar data

“…The 2D OSI expansion (12) can be exploited to reconstruct in a fast and accurate way the voltages V α and V δ at the points necessary for the plane-rectangular NFTFF transformation [7,8]. However, the probe corrected formulae in [8] (whose expressions in the here used reference system are shown in [25,26]) are valid only when the probe keeps its orientation with respect to the antenna and this enforces its co-rotation with it. A probe exhibiting only a first-order φ-dependence in its far field can be employed in order to avoid such a co-rotation.…”