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The computation of electromagnetic fields at non-asymptotic distances from an antenna using cylindrical near-field measurements
Dissertation (Ph. D.) -- University of Stellenbosch, 1992.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2012
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| _version_ | 1867613757640802304 |
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| access_status_str | Open Access |
| author | Du Toit, Cornelis Frederik |
| author2 | Cloete, J. H. |
| author_browse | Cloete, J. H. Du Toit, Cornelis Frederik |
| author_facet | Cloete, J. H. Du Toit, Cornelis Frederik |
| author_sort | Du Toit, Cornelis Frederik |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Dissertation (Ph. D.) -- University of Stellenbosch, 1992. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/69791 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:41:12.661Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2012 |
| publishDateRange | 2012 |
| publishDateSort | 2012 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/69791 The computation of electromagnetic fields at non-asymptotic distances from an antenna using cylindrical near-field measurements Du Toit, Cornelis Frederik Cloete, J. H. Stellenbosch University. Faculty of Engineering. Dept. of Electronic and Electrical Engineering. Electromagnetic fields -- Measurement -- Mathematics Antennas (Electronics) -- Measurement -- Mathematics Dissertations -- Electronic engineering Dissertation (Ph. D.) -- University of Stellenbosch, 1992. The well established theory of antenna near-field measurement techniques is normally used to determine the asymptotic far-field of an antenna. However, the more general problem of estimating the electromagnetic field at non-asymptotic distances from the antenna, which is the central theme of this thesis, is not addressed as widely. Since the asymptotic simplifications cannot be applied in this case, the evaluation of integrals with rapidly oscillating integrands is required. In general, these integrals cannot be evaluated in closed form, and the oscillatory nature of the integrands makes it extremely difficult to do so numerically. The problem is formulated in cylindrical co-ordinates and numerical methods for evaluating the integrals are investigated. These integrals describe the electromagnetic fields generated by an antenna in terms of cylindrical modal coefficients. The latter can in principle be determined from a complete set of far-field measurements of the antenna, but for practical reasons these are derived more efficiently from a set of near-field measurements. The principle used in evaluating the integrals is reminiscent of the method of stationary phase, whereby only infinitesimal neighbouring regions of the stationary phase points contribute to the value of the integral. After the identification of the stationary phase points, numerical integration is applied only to small but finite regions surrounding these points. The determination of the size of these regions, which has to be adjusted according to the required accuracy, is investigated. To minimize the error caused by truncation of the integration domain, the use of windows with various shapes as delimiters, is considered. Finally, a window shape is introduced which yields very good convergence in terms of accuracy versus domain size. The numerical integration methods examined, include Simpson's rule, Romberg integration, Gaussian quadrature, and Ludwig's method. Although more efficient algorithms would improve execution speed, Ludwig's method was selected for its simplicity and the ease with which the numerical error can be controlled. The cylindrical formulation yields electromagnetic field expressions in terms of Hankel functions. Algorithms for the numerical evaluation of these functions were developed, and represent a significant part of the work. Apart from the development of this essential numerical tool, approximate closed form expressions for Hankel functions also resulted from this study, which proved to be invaluable in factorizing the integrand and identifying stationary phase points in the integral evaluation problem described above. To test the integration procedure, simulation studies, as well as the comparison of experimental measurements with theoretical predictions, were carried out. Doctoral 2012-08-27T12:27:16Z 2012-08-27T12:27:16Z 1992 Thesis http://hdl.handle.net/10019.1/69791 en Stellenbosch University 201 pages : ill. application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Electromagnetic fields -- Measurement -- Mathematics Antennas (Electronics) -- Measurement -- Mathematics Dissertations -- Electronic engineering Du Toit, Cornelis Frederik The computation of electromagnetic fields at non-asymptotic distances from an antenna using cylindrical near-field measurements |
| title | The computation of electromagnetic fields at non-asymptotic distances from an antenna using cylindrical near-field measurements |
| title_full | The computation of electromagnetic fields at non-asymptotic distances from an antenna using cylindrical near-field measurements |
| title_fullStr | The computation of electromagnetic fields at non-asymptotic distances from an antenna using cylindrical near-field measurements |
| title_full_unstemmed | The computation of electromagnetic fields at non-asymptotic distances from an antenna using cylindrical near-field measurements |
| title_short | The computation of electromagnetic fields at non-asymptotic distances from an antenna using cylindrical near-field measurements |
| title_sort | computation of electromagnetic fields at non asymptotic distances from an antenna using cylindrical near field measurements |
| topic | Electromagnetic fields -- Measurement -- Mathematics Antennas (Electronics) -- Measurement -- Mathematics Dissertations -- Electronic engineering |
| url | http://hdl.handle.net/10019.1/69791 |
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