Student Number : 9713144D -
MSc Dissertation -
School of Electrical Engineering -
Faculty of Engineering and the Built Environment / The performance of the Log Periodic dipole array antenna has been characterized,
in the form of parametric curves available in most antenna design handbooks and
other relevant literature. These characteristic curves are often limiting in scope,
as for instance they do not contain parametric curves giving the relationship
between the boom-length 'L' and the number of dipole element 'N' for any given
bandwidth, even when it is known that these two parameters are the main cost
determinants of a LPDA Antenna. The concept of convergence is introduced to
aid cost optimization of the LPDA Antenna in terms of number of dipole element
'N'. Although 'N' is used as the minimization criterion, the criteria for establishing
convergence encompass all the main electrical characteristics of the LPDA
Antenna, such as VSWR, gain and radiation patterns. Lastly, the effects of boomimpedance
'Zo' and length to diameter ration 'Ln/Dn', on the performance
characteristics of the LPDA Antenna was investigated with the view to
determining if neglecting the effects of these two parameters were responsible for
the disparity in the directive gain values obtained by R. L Carrel compared to
those obtained by later researchers. The investigation indicates that if an LPDA
Antenna is converged, then the effects of Zo and Ln/Dn ratio though significant
can not alone account for the fairly large disparity in the gain values.
In other to perform these investigations, a modern scientific tool in the form of
numerical modeling by method of moments based, Super Numerical
electromagnetic code version2 was utilized. The numerical modeling tool was
first validated by agreement between measured values and the values as predicted
by the modeling tool. Next, simulation of the performance of LPDA antennas
under variations of their number of elements was done. Thereafter, the means and
standard deviations of the gain were extracted from the simulated numerical
models. Trends in the pattern of variation of the means and standard deviations of
the gain are used as the basis for deciding the value of number of element at
which the antenna can yield acceptable performance (convergence criteria). These
are presented as convergence curves, which gives for any given boom-length and operating bandwidth, the minimum number of elements required for the antenna
to yield acceptable performance.
Finally, the effect of length to diameter ratio and boom-impedance on the gain of
optimized LPDA antennas are presented as parametric curves.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/2164 |
| Date | 28 February 2007 |
| Creators | Onwuegbuna, Leonard Ikemefuna |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 71684 bytes, 55970 bytes, 180132 bytes, 66703 bytes, 178384 bytes, 413390 bytes, 104746 bytes, 41394 bytes, 85591 bytes, 52096 bytes, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf, application/pdf |
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