Thesis (MScEng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This thesis discusses the design of a dual circularly polarized single element antenna with special
emphasis on achieving a wide bandwidth and high polarization isolation. The aim of the study is to
produce an antenna for transmission of colour video signals between a ground station and a low
earth orbit satellite.
Microstrip patch antennas are suitable for satellite applications because they are light weight,
conformal and have a thin profile. However, the antennas' inherent naITOW bandwidth is one of
their major drawbacks. The aperture coupled microstrip patch antenna boasts of a much-improved
bandwidth over the traditional single layer microstrip antenna and the freedom of using separate
substrates for the patch and the feeding network. Hence the designed single element antenna is
aperture coupled. To achieve dual circular polarization with good polarization purity, the antenna
had a crossed slot aperture with a balanced feed. The feed network was designed on a single layer.
The design was executed in two steps using IE3D moment of methods simulation software: design
of the radiating part, and design of the feed part. Each part was simulated and optimized on its own
before the two were combined, simulated and optimized again. Parameters used in the antenna
optimization were: the substrates' thicknesses and dielectric constants, patch and aperture
dimensions, and the feed line width and offset.
The designed antenna was built and measured. Initial measurements of S-parameters yielded
unacceptable results, especially for S22 and S21, and so an investigation into the matter was
conducted. That led to the sizes of the feed and reflector planes being extended. Absorbing material
was used between the parallel feed and reflector planes because some power was, to a lesser extent,
still escaping, due to the fact that the planes were fmite.
Measurement results demonstrated reasonable agreement with the simulation. The final antenna had
a reflection coefficient of less than -10 dB for the entire operating band of 400 MHz centred on 3
GHz, an isolation of approximately -15 dB in the operating band and a gain of 2 dBi and I dBi for
Ports 1 and 2, respectively, at 3 GHz. These results, especially the gain, are influenced by the back
radiation and the finite sizes of the feed and reflector planes. It is therefore recommended that an
enclosed cavity be used at the back of the antenna and a 'dogbone' aperture be used to minimize
back radiation. / AFRIKAANSE OPSOMMING: Die tesis omskryf die ontwerp van 'n tweevoudige sikuler gepolariseerde enkel-element antenne
met spesiale klem op wye bandwydte en hoe polariserings isolasie. Die doel van hierdie studie is
om 'n antenne vir uitsending van kleur video seine tussen 'n grond stasie en 'n omnentelingsatelliet
daar te stel.
Mikrostrook plakantennes is gepas vir satelliet toepassings weens hulle ligte gewig en dun profiel.
Die antenne se gepaardgaande nou bandwydte is egter een van hulle grootste nadele. Die
gleufgekoppelde mikrostrook plakantenne gee egter 'n baie beter bandwydte as die tradisionele
enkellaag mikrostrook plakantenne asook die vryheid om verskillende substrate vir die plak en die
voernetwerkte gebruik. Vir hierdie redes daar besluit om die enkel-element antenne sleufgekoppeld
te maak. Om tweevoudige sikuler gepolariseerde met goeie polarisasie suiwerheid te kry, moes 'n
kruisvonnige gleuf met 'n gebalanseerde voer ontwerp word. Die voernetwerk was op 'n enkellaag
ontwerp.
Die ontwerp was in twee fases in IE3D momentmetode simulasie sagteware gedoen: ontwerp van
die stralings gedeelte, en ontwerp van die voer gedeelte. Elke gedeelte word afsonderlik gesimuleer
en geoptimiseer voordat die twee saam gesimuleer en geoptimiseer word. Parameters wat gebruik
word in die antenne optimiseering is: dikte van substraat en dielektriese konstante, plak en gleuf
grootes, en voer lynwydte en afwyking.
Die ontwerpde antenne is gebou en gemeet. Aanvanklike metings van S-parameters het
onaanvaarbare resultate gel ewer, vera I vir S22 en S21,dus is daar besluit om die redes daarvoor te
ondersoek. Dit het daartoe gelei dat die voer- en reflector vlakte groter gemmak is. Absorbeer
material is tussen die parallel voer- en reflector vlakke gebruik aangesien steeds drywing verloor is
weens die eindige vlakke.
Meting resultate het taarnlike goed met die simulasies vertoon. Die finale antenne het 'n
weerkaatskoeffisient laer as -10 dB getoon vir die volle bandwydte van 400 MHz gesentreerd
rondom 3 GHz, 'n isolasie van ongeveer -15 dB in die bandwydte en 'n aanwins van 2 dBi en I dBi
vir onderskeidelik Poorte I en 2 by 3 GHz. Hierdie resultate veral die aanwins is deur die straling
na agter beinvloed en die eindige grootes van die voer- en reflector vlakke. Dit word om hierdie
rede dus voorgestel dat 'n geslote holte aan die rugkant van die antenne gebruik word en dat 'n
"dogbone" gleuf gebruik word om straling na agter te minimeer.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/49818 |
| Date | 03 1900 |
| Creators | Maki, Pamela Ruth |
| 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 | 1 v. (various foliations) : ill. |
| Rights | Stellenbosch University |
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