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Multi-mode antennas for hemispherical field-of-view coveragePrinsloo, David Schalk Van der Merwe 03 1900 (has links)
Thesis ((PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This dissertation proposes a multi-mode antenna element excited through a multiconductor
feed. It is shown that each of the orthogonal transverse electromagnetic modes supported by
the antenna feed results in a unique radiated far-field pattern that collectively allow for nearhemispherical
field-of-view coverage.
Three multi-mode antenna designs are presented: a dual-mode antenna, integrating a single linearly
polarised dipole antenna with a co-located monopole, as well as two quad-mode antenna
designs integrating two dual-polarised dipole elements with a co-located monopole element.
The dual-mode antenna is excited through a balanced transmission line feed supporting both
differential- and common-mode signals that, respectively, result in typical dipole-over-ground
and monopole radiated far-field patterns. The quad-mode antennas are each fed through a
quadraxial transmission line allowing for excitation through four orthogonal transverse electromagnetic
port modes.
To characterise the multi-mode response of the multi-mode antennas, generalised transformations
are derived by which the multi-mode S-parameters and radiated far-fields can be calculated
from the S-parameters and far-fields corresponding to single-ended excitations. These transformations
are implemented to validate the response of a dual-mode and quad-mode antenna design
through measurements.
An equivalent network representation for active multi-mode antennas is presented, including generalised
transformations relating the multi-mode signal and noise response of the low-noise amplifiers
to the two-port S-parameters and noise parameters of the low-noise amplifiers. Through
the use of classical beamforming algorithms, the performance of an active dual-mode and quadmode
antenna is presented. In the case of the active dual-mode antenna, it is shown that through
the added use of common-mode signals, a variation in sensitivity of less than 50% is achieved
in the E-plane. Similarly, the additional excitation modes supported by the active quad-mode
antenna is shown to result in a significant improvement in the polarimetric capabilities over the
field-of-view coverage. / AFRIKAANSE OPSOMMING: Hierdie proefskrif stel ’n multimodale antenna element voor wat deur ’n multi-geleier transmissielyn
gevoer word. Dit word gewys dat elk van die ortogonale transversale elektromagnetiese
opwekkingsmodusse wat deur die antenna voer ondersteun word, ’n unieke vêrveld stralingspatroon
skep, wat gesamentlik lei tot ’n hemisferiese gesigsveld.
Drie multimodale antenna ontwerpe word voorgestel: ’n dubbelmodale antenna, waarin ’n enkel
lineêrgepolariseerde dipool antenna en monopool mede-geleë word, asook twee viermodale antenna
ontwerpe waarin twee dubbelgepolariseerde dipool elemente geïntegreer word met medegeleë
monopool antenna elemente. Die dubbelmodale antenna word gevoer deur ’n gebalanseerde
transmissielyn wat beide differensiële- en gemene-modus seine ondersteun, waar elk onderskeidelik
dipool-oor-aardvlak en monopool stralingspatrone voortbring. Die viermodale antennas
word elk gevoer deur vier-as transmissielyne wat vier ortogonale transversale elektromagnetiese
opwekkingsmodusse ondersteun.
Om die multimodale gedrag van die drie multimodale antennas te karakteriseer, word veralgemeende
transformasies afgelei waardeur die multimodale strooiingsparameters asook die vêrveld
stralingspatrone vanaf enkelpoort strooiingsparameters en vêrvelde bereken word. Hierdie transformasies
word toegepas om die gedrag van ’n dubbel- en viermodale antenna ontwerp te karakteriseer
deur metings.
Ekwivalente netwerkvoorstellings vir aktiewe multimodale antennas word voorgestel, insluitend
veralgemeende transformasies om die multimodale sein asook ruis gedrag van die lae-ruis versterkers
betreklik te maak tot die tweepoort strooiingsparameters en ruisparameters van die laeruis
versterkers. Deur gebruik te maak van klasieke bundelvormingsalgoritmes, word die gedrag
van aktiewe dubbelmodale en viermodale antennas voorgestel. Vir die aktiewe dubbelmodale
antenna word daar aangedui dat die gesamentlike gebruik van differensiële- en gemene-modus
seine, ’n variasie in sensitiwiteit onder 50% tot gevolg het in die E-vlak. Soortgelyk word daar
aangedui dat die addisionele opwekkingsmodusse wat deur die aktiewe viermodale antenna ondersteun
word, tot ’n beduidende verbetering in die polarisasievermoë oor die gesigsveld lei.
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Theory and Applications of Microstrip/Negative-refractive-index Transmission Line (MS/NRI-TL) Coupled-line CouplersIslam, Rubaiyat 09 January 2012 (has links)
The electromagnetic coupling of a microstrip transmission line (MS-TL) to a metamaterial backward wave Negative-Refractive-Index transmission line (NRI-TL) is the primary investigation of this dissertation. The coupling of forward waves in the MS-TL to the backward waves in the NRI-TL results in the formation of complex modes, characterized by simultaneous phase progression and attenuation along the lossless lines.
Through network-theoretic considerations, we investigate the properties of these modes in the complex-frequency plane of the Laplace domain to help unravel the confusion that has existed in the literature regarding the independent excitation of a pair of conjugate complex modes. We show that it is possible to arbitrarily suppress one of the modes over a finite bandwidth and completely eliminate it at a discrete set of frequencies using proper source and load impedances. Hence we use conjugate modes with independent amplitudes in our eigenmode expansion when we analyse various coupling configurations between the two types of lines (MS/NRI-TL coupler).
We derive approximate closed-form expression for the scattering parameters of the MS/NRI-TL coupler and these are complemented by design charts that allow the synthesis of a wide range of specifications. Moreover, these expressions reveal that such couplers allow for arbitrary backward coupling levels along with very high-isolation when they are made half a guided wavelength long. The MS/NRI-TL coupler offers some interesting applications which we highlight through the design and testing of a 3-dB power splitter, a high-directivity signal monitor and a compact corporate power divider. We have included design, simulation and experimental data for the fabricated prototypes exhibiting good agreement and thereby justifying the theory that has been developed in this work to explain the coupling between a right-handed MS-TL and a left-handed NRI-TL.
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Theory and Applications of Microstrip/Negative-refractive-index Transmission Line (MS/NRI-TL) Coupled-line CouplersIslam, Rubaiyat 09 January 2012 (has links)
The electromagnetic coupling of a microstrip transmission line (MS-TL) to a metamaterial backward wave Negative-Refractive-Index transmission line (NRI-TL) is the primary investigation of this dissertation. The coupling of forward waves in the MS-TL to the backward waves in the NRI-TL results in the formation of complex modes, characterized by simultaneous phase progression and attenuation along the lossless lines.
Through network-theoretic considerations, we investigate the properties of these modes in the complex-frequency plane of the Laplace domain to help unravel the confusion that has existed in the literature regarding the independent excitation of a pair of conjugate complex modes. We show that it is possible to arbitrarily suppress one of the modes over a finite bandwidth and completely eliminate it at a discrete set of frequencies using proper source and load impedances. Hence we use conjugate modes with independent amplitudes in our eigenmode expansion when we analyse various coupling configurations between the two types of lines (MS/NRI-TL coupler).
We derive approximate closed-form expression for the scattering parameters of the MS/NRI-TL coupler and these are complemented by design charts that allow the synthesis of a wide range of specifications. Moreover, these expressions reveal that such couplers allow for arbitrary backward coupling levels along with very high-isolation when they are made half a guided wavelength long. The MS/NRI-TL coupler offers some interesting applications which we highlight through the design and testing of a 3-dB power splitter, a high-directivity signal monitor and a compact corporate power divider. We have included design, simulation and experimental data for the fabricated prototypes exhibiting good agreement and thereby justifying the theory that has been developed in this work to explain the coupling between a right-handed MS-TL and a left-handed NRI-TL.
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