Formulation of Probe-Corrected Time-Domain Planar Near-Field Measurements
Rept. for Sep 1992-Aug 1993
ROME LAB HANSCOM AFB MA
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Probe-corrected planar near-field formulas in the time domain are derived for both acoustic and electromagnetic fields, so that a single set of near-field measurement in the time domain yields the fields of the test antenna directly in the time domain. The time-domain probe-corrected formulas are first derived by taking the inverse Fourier transform of the corresponding frequency- domain formulas, and then by using a time-domain expansion for the fields of the test antenna and a time-domain receiving characteristic of the probe. Because these general formulas, which involve a double integral over the scan plane and an infinite time-convolution integral, are rather complicated, we consider a special probe whose output due to an incoming time-domain plane wave is proportional to the time derivative of the field of that plane wave. For this special D-dot probe, the probe-corrected formulas simplify to give the time- domain far-field pattern as a double spatial integral of the time-domain output of the prove over the scan plane multiplied by the angular dependence of the receiving characteristic of the probe. Time-domain reciprocity relations are derived for reciprocal probes, and their time-domain receiving characteristics are related their far fields. Finally, a time-domain sampling theorem is derived and a numerical example illustrates the use of the time-domain probe-corrected formulas. Near-field measurements, Planar scanning, Time domain, Probe correction.
- Electricity and Magnetism