Formulation of Time-Domain Planar Near-Field Measurements Without Probe Correction
Rept. for Sep 1991-Aug 1993
ROME LAB HANSCOM AFB MA
Pagination or Media Count:
This report addresses the problem of formulating planar near-field antenna measurements in the time domain, so that a single set of time-domain near-field measurements yields the far-field pattern in the time domain or over a wide range of frequencies. The time-domain planar near-field techniques are developed for both acoustic and electromagnetic fields and the space outside the region occupied by the antenna is assumed to be isotropic and homogeneous. Probe correction is ignored, that is, it is assumed that the probe is ideal so that the exact values of the field on the measurement plane are known. Two fundamentally different approaches are used in deriving time-domain formulas which give the fields in the half space z z sub 0, in terms of their values on the plane z z sub 0. In the first approach the time-domain formulas are obtained by inverse Fourier transforming the corresponding frequency-domain formulas. Since this approach requires extensive use of the frequency domain near-field formulas, we start by giving a rigorous derivation and review of the frequency-domain formulation that addresses a number of subtleties that have not been dealt with adequately in the literature. As part of this review, planar near-field formulas for the static electric and magnetic fields are derived for the first time. In the second approach the time-domain near-field formulas are derived directly in the time domain. The equivalence of the resulting time- domain formulas obtained by the two different approaches demonstrates the validity of the formulas and the utility of both approaches. Near-field measurements, Planar scanning, Time-domain.
- Electrical and Electronic Equipment
- Radiofrequency Wave Propagation