A thesis submitted to the Faculty of Engineering and the Built
Environment, University of the Witwatersrand, Johannesburg, in
fulfilment of the requirements for the degree of Doctor of Philosophy.
Johannesburg, 2017 / The scientific requirements for Radio Frequency (RF) receivers especially for Radio Astronomy
have become more demanding, requiring: compact, low-profile, multi and wideband
antennas and more sensitive receivers. Integration of the antenna into the receiver
system is often critical to meet these demands.
Noise theory to model these more complex systems is well developed but is not implemented
in commercial solvers, given the niche market of the receivers it is only available
using specialised software. If the system is closely coupled, it becomes necessary for design
to incorporate Electromagnetic (EM) and Microwave (MW) modelling into the multi port
noise modelling. CAESAR, a combined noise and EM/MW modelling code is available, but
to use it requires the exclusive use of the CAESAR software, which is impractical given the
utility and wide use of commercial solvers.
Mathematical methods are developed to incorporate commercial solvers into the more
specialised CAESAR, validated using a folded dipole and applied to a wideband Eleven antenna
system, a compact form of a log periodic dipole array. The Eleven antenna consist
of eight single ended or four differential ports, with a closely coupled feeding arrangement.
Cryogenic measurements are done to verify the modelling, the measured sensitivity
matches with the model closely in amplitude and shape, giving confidence to the approach,
and allowing modelling but not system optimisation.
Optimising the antenna based on receiver design and still being able to use commercial
code requires the external scripting of a commercial solver. The EDITFEKO (card based)
module of FEKO (a powerful and versatile solver) is used along with the meshing software
GMSH and GNU Octave. Optimisation of system sensitivity is demonstrated on a choke
horn fed reflector system at 1420MHz.
This optimisation method is applied to a practical application, an octave band system
(4:5 GHz to 9 GHz) for the Hartebeesthoek Radio Observatory. The design is split into
smaller simulations using waveguide modes and the associated S–parameters, the techniques
are presented and checked on a truncated system. Initial design and optimisation
are given.
The combining of specialised multiport noise modelling design and optimisation within
commercial EM/MW solvers allows more sensitive and specialised receivers to be built.
Index terms— noise modelling, wideband, multiport, corrugated horn, octave band receiver,
EM/MW optimisation / MT2018
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/24241 |
| Date | January 2017 |
| Creators | Klein, Benjamin |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (xv, 154 leaves), application/pdf, application/pdf |
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