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Title:Switched aperture surface current measurements
Author(s):Gibbons, Brian B.
Director of Research:Bernhard, Jennifer
Doctoral Committee Chair(s):Bernhard, Jennifer
Doctoral Committee Member(s):Franke, Steven; Schutt-Ainé, José; Bahl, Gaurav
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):surface current measurement
surface current probe
magnetic field probe
switched aperture measurement
aperture coupling
slot coupling
surface currents
RF currents
microwave currents
antenna currents
Abstract:The measurement of induced surface currents on antennas, scatterers, and other structures is important for a variety of reasons, including in-situ measurements and validation of simulated results. Techniques for measuring the complete vector nature of surface currents (magnitude, direction, and phase) have relied on probes that perturb the spatial structure of the field. Provided this perturbation is sufficiently small and/or well-characterized, reasonably accurate results may be obtained. In other words, these methods assume that the perturbed fields are sufficiently similar to the unperturbed fields that measurements of the former may be substituted for values of the latter. In this work, a general theory referred to as a switched aperture surface current measurement is developed that directly obtains unperturbed electric surface current measurements, provided certain conditions on the measurement apparatus are met. The most stringent of these are the requirement for a backplane region, fully isolated from the measurement environment, and the requirement that the environment and sources generating the currents do not change significantly when a measurement aperture is switched between open and shorted states. Provided these conditions are met, the theory removes the conventional measurement probe trade-off between measurement accuracy and probe size, since probe size is conventionally proportional to signal-to-noise ratio and inversely proportional to field disturbance and hence accuracy. This theory should thus allow for the creation of highly accurate surface current measurement apparatuses in special cases. The relevant background and supporting theory are developed here for the switched aperture measurement technique, followed by the development and analysis of two calibration theories necessary to utilize the technique in practice. An in-depth study of a simulated, example measurement apparatus is conducted, which is used to draw a number of conclusions and to propose future work.
Issue Date:2018-05-17
Rights Information:Copyright 2018 Brian B. Gibbons
Date Available in IDEALS:2018-09-27
Date Deposited:2018-08

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