Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: An antenna for ground level deployed Ground Penetrating Radar applications is presented. The
antenna is matched to the ground via a low impedance dielectric matching section improving the
radiation pattern and input impedance characteristics.
A bowtie antenna was used for the design with the edges rounded to stabilize the resonant
frequency. The radiation pattern was focused to the one side of the antenna for ground
penetration using a non-absorptive metallic cylindrical air filled cavity. Edge reflections from the
antenna were reduced by means of discrete resistor terminations between the antenna and the
cavity. A wire equivalent of the solid metallic antenna was investigated giving similar
characteristics to that of the solid antenna.
The radiation pattern deformation arising from transmitting a wave from an antenna in air into the
ground due to the impedance mismatch was investigated. This was overcome with the use of a
polypropylene dielectric slab inserted between the antenna and the ground. Together with
improving the radiation pattern the antenna was less sensitive to ground parameter variations and
to an air gap introduced between the slab and the ground. This was implemented as a wheel
mounted system with adjustable height settings depending on the terrain.
A pair of mounted antennas was constructed to be tested on an existing bistatic Stepped
Frequency Continuous Wave radar operating in the 50-400 MHz band developed by the
University of Cape Town.
This antenna is seen as providing a solution to the problem of coupling an antenna to a low wave
impedance medium such as ground. / AFRIKAANSE OPSOMMING: 'n Antenne word vir Grond Penetrerende Radar toepassings voorgestel. Dit is spesifiek ontwikkel
vir oppervlak ontplooide stelsels ontwerp. Die antenne is aangepas tot die grond deur middel van
'n diëlektriese aanpassingseksie wat die starlingspatroon en intree-impedansie karakteristieke
verbeter.
Die antenne is tot die grond toe aangepas deur middel van 'n diëlektriese aanpassingseksie wat
die starlingspatroon en intree-impedansie karakteristieke verbeter.
'n Strikdas antenne was gebruik vir die ontwerp, met die kante gerond om die resonante
freqwensie te stabiliseer. Om die stralingspatroon van die antenne na een kant toe te fokus was 'n
nie-absorbeerede metaleiese, luggevulde, silindriese holte daaragter geplaas om die energie
vorentoe te weerkaats. Weerkaatsings van die rand van die antenne word onderdruk met behulp
van koppelende weerstande tussen die antenne en die holte. A draad ekwivalent van die antenne
was ook ondersoek met goeie ooreenstemming met die soliede strikdas.
Die impedansie wanaanpassing wat ontstaan as 'n antenne wat in lug is, in die grond in straal
veroorsaak dat die stralingspatroon van die antenne vervorm word. Dit was gevind dat deur 'n
aanpassings blad van 'n diëlektriese materiaal, naamlik polipropileen, gebruik te maak tussen die
antenne en die grond dat dit die probleem oplos. Saam met dit was gevind dat die antenne minder
sensitief was vir veranderings in grondparameters en ook vir 'n lug gaping tussen die blad en die
grond. Die het gemaak dat die antenne op wiele gemonteer kon word met verstelbare hoogte
afhangend van die terrein.
'n Stel geskaleerde antennes was gemaak om op 'n beskikbare bistatiese Trap Frekwensie
Kontinue Golf radar te werk. Dit werk oor die 50-400 MHz band en was ontwikkel deur die
Universitiet van Kaapstad.
Die antenne word gesien as 'n oplossing vir antenne koppelingsprobleme ondervind by laë golf
impedansie materiale.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52186 |
| Date | 12 1900 |
| Creators | Birch, Max (Max Lariviere) |
| Contributors | Palmer, K. D., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 59 p. : ill. |
| Rights | Stellenbosch University |
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