Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / This thesis focuses on the coaxial-microstrip T-resonator measurement technique to
determine the aperture plane capacitance and radiation resistance of electrically short
monopoles above a finite ground plane at Radio Frequencies. The determination of
these impedance parameters is of interest as they are needed in the Thévenin
equivalent circuit of the monopole to establish the relationship between the monopole,
the electromagnetic field within which it is immersed, and its surrounding medium
properties. Electromagnetically short monopoles are used in various applications such
as in permittivity and biomedical measurement techniques and near-field metrology.
The coaxial-microstrip device allows the measurement of transmission coefficient
nulls when connected to the network analyser. By measuring the frequency shift in
transmission null points and analysing the results, the capacitance of short monopoles
of various lengths can be obtained. The radiation resistance of the monopole can also
be determined by comparing the depth of transmission coefficient nulls points at
various resonant frequencies.
Monopoles ranging from flush-mounted to various sizes of protruding centre
conductors, both bare and insulated, are investigated in the frequencies ranging from
45 MHz to 3 GHz. The experimental results compare well with FEKO numerical
predictions at the ranges where this technique is applicable. The technique is however
not applicable near and beyond the resonant frequency of the monopole where it is
considered to be electrically long.
Measurements to obtain monopole impedance parameters were conducted by
connecting the device to the HP 8510C Network Analyser. To enhance accuracy, the
Network Analyser was calibrated using a high quality calibration kit with precisely
defined standards. The technique used was found to accurately yield capacitances in
the range of 0.0211 to 1 pF and radiation resistances in the range of 0.9245 to 12.1
Ohms. These results were obtained for monopoles of length 0.0062 < h/l < 0.24.
Results from literature, viz. W.R Scott, R.W.P. King and L.J. Cooper, show radiation
resistance in the ranges: 2.5 to 35 Ohms (0.079 < h/l < 0.22), 1.26 to 74.08 Ohms (0.026 < h/l < 0.28) and 5.59 to 74.98 Ohms (0.1 < 0.28) for electrically short
monopoles. The results of this work are compared with those in the literature and
show variations of less than 6%.
A technique capable of accurately measuring capacitance and radiation resistance of
the monopole at various lengths of protruding centre conductor has been developed.
The capacitance for a flush probe compares very well (agreement is less than 6%)
when compared with those obtained by the previous researchers. The technique is
capable of yielding accurate results radio frequencies in the challenging low radiation
resistance range around 1 Ohm.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1501 |
| Date | 12 1900 |
| Creators | Kwinana, Phumezo M. |
| Contributors | Cloete, J. H., University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 2172606 bytes, application/pdf |
| Rights | University of Stellenbosch |
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