NF-FFNear Field to Far Field Transformation
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Through the NF-FF method, the affection of electron density to the radiation characteristic of plasma antenna is studied.
Through the NF-FF transformation, we obtain the far-field radiation pattern.
In this framework, the application of the spatial bandlimitation properties of radiated EM fields [30] and of their nonredundant sampling representations [31, 32] to the voltage measured by the scanning probe has allowed the development of effective nonredundant probe-compensated NF-FF transformation techniques.
Accurate, stable, and effective, nonredundant NF-FF transformations with helicoidal scanning [33, 36-42], planar [37, 42-44], and spherical [37, 42, 45-52] spiral scannings (Figures 1, 2, and 3) have been developed in the last years.
Moreover, direct NF-FF transformations with helicoidal scanning, which allow the evaluation of the antenna far field in any cut plane directly from a minimum set of NF data without interpolating them, have been recently proposed in [56-58].
Note that, unlike as done in [7], where for simplicity an ideal probe was assumed, the effects of the measurement probe are properly taken into account here so that the developed NF-FF transformations are probe-compensated.
It is then possible to recover the NF data needed to perform the spherical NF-FF transformation [9], as modified in [12,13].
At last, the developed interpolation algorithm has been applied to retrieve the NF data required to carry out the spherical NF-FF transformation [9], as modified in [12,13].
Among the NF-FF transformations, that employing the spherical spiral scanning [23-28], as well as that employing the spherical one [12,13,16,34-36], have attracted considerable attention, since they allow the full reconstruction of the AUT radiation pattern, even though the data processing is considerably more complex than that needed by planar and cylindrical NF facilities [1, 2].
The NF-FF transformation with spherical spiral scan [28], using the two-bowls modelling (Fig.
Another method for the NF-FF transformation is proposed to consider the full probe correction through the diagonal translation operator [15].
One primary attraction of the conventional NF-FF transformation method is the employment of the free space DGF.