Dissertations / Theses on the topic 'Complementary antenna'

Abstract This dissertation presents wideband and multi-element antennas for mobile applications. It is divided into the following main parts: modal theory, wideband antennas, multi-element antennas, and wideband multi-element antennas. The radiating fields are first studied in terms of spherical scalar and vector modes, and it is shown how these modes correlate with the characteristic current modes on a planar mobile ground plane. The theory part shows how it is possible to excite the same modes on a conventional sphere and a rectangular planar mobile ground plane. The theory refers to the novel wideband antenna structures presented in this dissertation, in terms of current and radiating modes. After studying the modes, the dissertation shows how to excite a radiating antenna mode within a wide frequency bandwidth. To gain this, two main approaches are taken. First, a quasi-complementary antenna (QCA) structure with an electric conductor and magnetic slot is presented, and its characteristics are studied. A QCA UWB antenna, and a QCA element excited with a monopole or a dipole, is presented. The QCA structure compensates for the imaginary part of the input impedance on wide frequency bandwidth, when, at the same time, the fundamental mode is excited to ensure good radiating properties. The second approach uses a symmetrical feeding with two antenna elements to gain a wide frequency bandwidth, the relative -6 dB impedance bandwidth between 37.5–80%. When a field is symmetrically coupled to the conducting ground plane, the excitation avoids the awakening of higher order modes which might disturb the performance of the antenna. It is also shown, by using multiple feeding elements, that the excitation of orthogonal higher order modes on a small radiating ground plane is possible. As the modes are orthogonal to each other, they present a very low correlation. By using this kind of approach, radiation pattern diversity can be obtained in mobile applications within a small volume. On the other hand, when combining two QCA elements to a one multi-element antenna structure, a wideband diversity antenna with an 87.5% relative -6 dB impedance bandwidth, and a wideband MIMO antenna with a 95.0% relative -6 dB impedance bandwidth, are presented with excellent radiation and correlation properties. Also mutual coupling is need to be counted when multi-element antennas are designed. When designing an efficient radiator, it is important to consider an antenna feeding in terms of wideband impedance matching and wideband baluns, not to spoil the antenna performance. The efficient antenna structures and feeding mechanisms are obtained by using commercial 3D electromagnetic simulators to find the desired wideband antenna characteristics. Prototype antennas are measured in most of the presented structures to show their functionality in real. In general, the dissertation presents wideband antenna structures with radiating antenna modes excited on a planar conducting ground plane. The idea is to find structures and feeding mechanisms to excite the fundamental mode, or a certain radiating antenna mode, at a wide frequency bandwidth, by avoiding the excitation of higher order modes which might disturb the antenna performance. It is also shown that, by using multiple feeding elements, it is possible to excite higher order modes on a small antenna
Tiivistelmä Väitöskirjassa esitetään uusia laajakaistaisia ja monielementtiantenneja matkaviestimiin. Väitöskirja koostuu neljästä pääalueesta: pintavirtojen muototeoria, laajakaistaiset antennit, monielementtiantennit sekä laajakaistaiset monielementtiantennit. Teoriaosassa säteilykenttiä on aluksi tutkittu pallon pinnalla sekä skalaaripotentiaaleina että pintavirtavektoreina, jonka jälkeen niitä on verrattu mobiilin laitteen maatason ominaispintavirtojen synnyttämiin säteilykenttiin. Teoriaosassa osoitetaan, että pallon pinnalla sekä tasomaisella suorakaiteen muotoisella pinnalla on mahdollista herättää samat säteilykentät. Myöhemmin väitöskirjassa esitettävien uudenlaisten antennirakenteiden ominaisuuksia verrataan teoriaosassa esitettyihin pintavirtoihin ja säteilykenttiin. Teoriaosuuden jälkeen osoitetaan miten säteilevä sähkömagneettinen kenttä saadaan herätettyä laajalla taajuusalueella. Tähän on otettu kaksi eri lähestymistapaa, joista ensimmäisessä esitellään ja tutkitaan kvasikomplementaarista antennirakennetta (QCA). Kvasikomplementaarisessa antennirakenteessa sisääntuloimpedanssin imaginaariosa kompensoidaan yhdistämällä sähköinen johde ja magneettinen rako samaan antenniin. Samanaikaisesti perusmuoto herätetään laajalla taajuusalueella, jolla varmistetaan antennin hyvät säteilyominaisuudet koko toimintataajuusalueella. Toisessa lähestymistavassa käytetään kahta symmetrisesti asetettua antennielementtiä, joita syötetään symmetrisesti samalla amplitudilla ja vaiheella. Kun sähkömagneettinen kenttä herätetään symmetrisesti, korkeamman kertaluvun muotojen herättäminen voidaan välttää laajalla taajuusalueella. Symmetrisesti syötetyillä antennirakenteilla saavutettu -6 dB suhteellinen impedanssikaistanleveys on 37.5–80 %. Useita syöttöelementtejä käytettäessä voidaan mobiilin laitteen maatasossa herättää yhdellä pistetaajuudella monta toisistaan riippumatonta säteilykenttää. Koska herätetyt kentät ovat toisistaan riippumattomia, on niiden välinen korrelaatio myös pieni. Kyseisellä rakenteella on mahdollista toteuttaa säteilykuviodiversiteetti erittäin pienessä tilassa, kuten matkapuhelimessa. Toisaalta, kun yhdistetään kaksi QCA-elementtiä yhdeksi monielementtiratkaisuksi, voidaan toteuttaa laajakaistainen diversiteettiantenni, jonka suhteellinen -6 dB impedanssikaistanleveys on 87.5 %. Vastaavasti kahdella laajakaistaisella QCA-elementillä toteutetulla MIMO-ratkaisulla päästään 95 % suhteelliseen -6 dB impedanssikaistanleveyteen. Molemmilla ratkaisuilla on erittäin hyvät säteilyominaisuudet sekä alhainen korrelaatio ja pieni keskinäiskytkentä antennielementtien välillä. Suunniteltaessa toimivaa laajakaistaista antennirakennetta, on tärkeää ottaa huomioon antennisyötön impedanssisovitus, jotta antennin suorituskyky ei heikkenisi. Lisäksi balansoidussa rakenteissa tulee olla laajakaistainen baluni, jolla vältetään säteilykuvion vääristyminen. Väitöskirjan syöttöratkaisuissa on käytetty kaupallisia sähkömagneettisia simulaattoreita, joilla antennirakenne voidaan mallintaa kolmiulotteisesti, ja joilla laajakaistainen syöttö saadaan optimoitua haluttuun antenniin. Suurin osa esitellyistä antennirakenteista on simulointien lisäksi myös mitattu, jolloin niiden toimivuus käytännössä pystytään todentamaan rakentamalla prototyyppiantenni. Yleisesti väitöskirjassa esitellään tasomaisia antenniratkaisuja johtavassa maatasossa, joissa säteilevät pintavirrat herätetään mahdollisimman laajalla taajuusalueella. Ideana on löytää laajakaistaisia antenni- ja syöttörakenteita, joilla saadaan herätettyä perusmuoto tai jokin muu haluttu muoto. Ajatuksena on välttää korkeamman kertaluvun muotojen herättäminen, jotka voivat pilata antennin suorituskyvyn. Väitöskirjassa osoitetaan myös, että pienikokoisella antennilla on mahdollista herättää korkeamman kertaluvun muotoja pistetaajuudella käyttämällä useita heräte-elementtejä

Fast and accurate diagnosis is always in demand by modern medical professionals and in the area of national defense. At present, limitations of testing speed, sample conditions, and levels of precision exist under current technologies, which are usually slow and involve testing the specimen under laboratory conditions. Typically, these methods also involve several biochemical processing steps and subsequent detection of low energy luminescence or electrical changes, all of which reduce the speed of the test as well as limit the precision. In order to solve these problems and improve the sensing performance, this project proposes an innovative CMOS magnetic biological sensor system for rapidly testing the presence of potential pathogens and bioterrorism agents (zoonotic microorganisms) both in specimens and especially in the environment. The sensor uses an electromagnetic detection mechanism to measure changes in the number of microorganisms--tagged by iron nanoparticles--that are placed on the surface of an integrated circuit (IC) chip. Measured magnetic effects are transformed into electronic signals that count the number and type of organisms present. This biosensor introduces a novel design of a conical-shaped inductor, which achieves ultra-accuracy of sensing biological pathogens. The whole system is integrated on a single chip based on the fabrication process of IBM 180 nm (CMOS_IBM_7RF), which makes the sensor small-sized, portable, high speed, and low cost. The results of designing, simulating, and fabricating the sensor are reported in this dissertation.
Ph. D.

The explosive growth of wireless communication market has led the development of low-cost, highly-integrated wireless communication systems. Even though most blocks in the front-end have successfully been integrated by using the CMOS technology, it is still a formidable challenge to integrate the entire front-end. Thus, the objective of this research is to demonstrate the feasibility of the integrated front-end by using improved circuit techniques as well as the improved process technologies. This dissertation proposes an improved control scheme to enhance the high-power handling capability of an antenna switch. As a part of this research, an antenna switch controller for a GaAs antenna switch was first developed to enhance the performances of the GaAs antenna switch by using the boosted control voltage. To enhance the efficiency of the front-end, efficiency improvement techniques for the antenna switch controller has also been studied. With the suggested efficiency improvement techniques, a fully-integrated antenna switch was implemented using the SOI technology, and exceeding performances over many commercial products for watt-level high-power applications have been successfully demonstrated. As an effort to improve the efficiency of a power amplifier, a linear envelope detector was also implemented, and the results show that the envelope detector is suitable for dynamic biasing of the power amplifier. The research presented in this dissertation, thus, provides a low-cost and high-performance solution for highly-integrated RF front-end used in various wireless communication systems.

This diploma thesis deal with the design of log-periodic antenna. The log-periodic antenna is self-complementary and broadband antenna. Antenna self-complementary structures are described only by angles. Input impedance of log-periodic antenna is equal to theoretical impedance ohms. The input impedance and radiation patterns of broadband antenna structures are independent of frequency over theoretically unlimited bandwidths. The log-periodic antennas provide linearly polarized radiation pattern. In this thesis is designed antenna for bandwidths 1 to 5GHz. In this diploma thesis is introduced design balanced unit, this is compound broadband balun and broadband impedance transformer. The broadband balun is based on conversion of microstrip line to balanced stripline. The Klopfenstein impedance taper is used for design. For simulation was used software from firma Zeland software IE3D.

In recent years, tremendous growth of the wireless market can be defined through the following words: smartphone and high-data rate wireless communication. This situation gives new challenges to RF power amplifier design, which includes high-efficiency, multi-band operation, and robustness to antenna mismatch conditions. In addition to these issues, the industry and consumers demand a low-cost small-sized wireless device. A fully integrated single-chip CMOS transceiver is the best solution in terms of cost and level of integration with other functional blocks. Therefore, the effective approaches in a CMOS process for the abovementioned hurdles are highly desirable. In this dissertation, the new challenges are overcome by introducing adaptability to a CMOS power amplifier. Meaningful achievements are summarized as follows. First, a new CMOS switched capacitor structure for high power applications is proposed. Second, a dual-mode CMOS PA with an integrated tunable matching network is proposed to extend battery lifetime. Third, a switchless dual-band matching structure is proposed, and the effectiveness of dual-band matching is demonstrated with a fully-integrated CMOS PA. Lastly, a reconfigurable CMOS PA with an automatic antenna mismatch recovery system is presented, which can maintain its original designed performance even under various antenna mismatch conditions. Conclusively, the research in this dissertation provides various solutions for new challenges of advanced mobile terminals.

Une antenne auto-complémentaire possède des caractéristiques radioélectriques très intéressantes en ce qui concerne l'élargissement de sa bande passante. Basée sur le principe de Babinet, l'auto-complémentarité permet en effet de maximiser la largeur de bande de par la complémentarité air-métal dans la structure de l'antenne. L'objectif de cette thèse est d'étudier quels pouvaient être les apports de l'auto-complémentarité dans le cas d'antennes à fortes contraintes d'intégration telles que celles utilisées pour les terminaux mobiles. Pour tester les limites de notre étude, nous avons choisi d'appliquer nos résultats à l'intégration d'antennes auto-complémentaires dans un objet communicant de type Smartphone multi-standards. Les antennes dites AC doivent par conséquent satisfaire de nombreux critères de performances tout en montrant leur capacité d'intégration. Celle-ci est rendue d'autant plus délicate, que la miniaturisation implique à son tour des phénomènes physiques limitant certaines performances, notamment en basse fréquence avec la nouvelle bande LTE. Dans une première étude, nous avons considéré différentes antennes et opté pour les antennes IFA-AC sur un plan de masse fini afin de couvrir initialement les bandes hautes DCS/PCS/UMTS et WLAN/LTE2600. Dans une seconde étude, nous avons amélioré leurs performances à l'aide d'éléments structurels nouveaux et interdépendants (éléments rayonnants de type double IFA), qui nous ont permis d'obtenir des résultats probants relatifs notamment à la couverture des bandes LTE800 et GSM. Enfin, nous avons complété notre projet en optimisant le lien radio par l'intégration de plusieurs éléments rayonnants AC sur un même PCB.

Thesis (M.Eng.(Microelectronic Engineering))--University of Pretoria, 2009.
Includes summaries in Afrikaans and English. Includes bibliographical references (leaves [74]-78). Mode of access: World Wide Web.

Les métamatériaux à indice de réfraction négative ont attiré énormément l'attention ces dernières années surtout à cause de leurs propriétés électromagnétiques uniques. Ces matériaux sont des structures artificielles qui présentent des caractéristiques n'étant pas disponibles en matériaux naturels. Récemment, le développement technologique avec de nouvelles techniques de fabrication offrent un grand nombre de nouvelles application et développement de nouveaux matériaux. Il est possible d'obtenir un métamatériau en combinant des structures artificielles périodiquement. Les propriétés uniques du Split Ring Resonator (SRR), les Surfaces à Haute Impédance (HIS), les Surface Sélective en Fréquence (FSS) sont étudiées ainsi que les métamatériaux composés. Il a été démontré avec succès l'utilisation pratique de ces structures dans les circuits et les antennes. Il a été confirmé expérimentalement que les métamatériaux pourrait améliorer la performance des structures considérées dans cette thèse, pour des fréquences où la bande interdite électromagnétique se produit.

Les milieux humides sont menacés par le changement climatique et l'anthropisation des milieux naturels. La télédétection est un moyen efficace de suivre des variables environnementales sur de grands espaces. Cependant, lorsqu’il s’agit de l’étude de la dynamique hydrologique, une résolution temporelle importante est indispensable. Or celle-ci est difficilement accessible par l'imagerie optique satellitaire du fait de l’important couvert nuageux qui masque le sol. Les capteurs radars, travaillant dans le domaine des micro-ondes, sont tout particulièrement adaptés à la caractérisation des dynamiques hydrologiques grâce à la sensibilité de leurs mesures en présence d’eau et ce quelque soit la végétation en place. Il en découle que toutes les acquisitions Radar à Synthèse d’Ouverture (RSO) sont exploitables, acquises de jour comme de nuit, quel que soit le couvert nuageux.Récemment la télédétection radar satellitaire a vécu une véritable révolution grâce au lancement du satellite Sentinel-1A en 2014 suivi de son jumeaux Sentinel-1B deux ans plus tard par l'Agence Spatiale Européenne dans le cadre du programme Copernicus. Ces capteurs acquièrent des données en bande C (λ = 5,6 cm) sur toute l'Europe chaque 12 jours par satellite et leur diffusion est libre et gratuite pour tous. Le présent travail de thèse vise à évaluer le potentiel de ces données à haute résolution temporelle pour le suivi des surfaces d'eau et des milieux humides.Dans une première partie consacrée à la cartographie des surfaces d'eau, nous avons identifié une confusion la réponse radar en bande C des surfaces d'eau et celle de certains sols nus. Nous avons alors montré que la période hivernale est celle qui présente le moins d’ambiguïté et que la polarisation VH est la plus adaptée à la cartographie des surfaces en eau. Quatre méthodes de détection des zones en eau ont été comparées, il résulte que l’utilisation de méthodes non-supervisées sans données a priori n'est pas envisageable et que les méthodes prenant en compte le voisinage spatial donnent de meilleurs résultats. Un filtrage temporel a été mis au point et a permis d'améliorer la détection et de s'affranchir des confusions entre sols nus et surfaces d'eau permanentes. Les surfaces d'eau de plus de 0,5 ha ont plus de 80 % de chances d'être détectées.Un second volet de cette thèse est consacré au suivi d'une zone humide prairiale par télédétection radar. L'utilisation d'images pleinement polarimétriques a montré que la configuration de polarimétrie partielle VV/VH disponible sur le capteur de Sentinel-1 permet de caractériser l'inondation prairiale avec ou sans végétation. Une méthode prenant en compte l'information de voisinage temporel a permis de traiter une série de 14 images Sentinel-1 pour obtenir 14 cartes d'inondation pour l’année 2015. Une estimation de la précision à l'échelle intra-parcellaire a été mise au point, il apparaît que si la précision est relativement bonne (80 %), le rappel est assez bas (40 %). Cette méthode permet d'établir des bilans d'évolution intra- et inter-annuels.Cette thèse a montré le potentiel de l'utilisation d'images radar à haute résolution temporelle tant pour la cartographie des surfaces en eau que pour le suivi d'une zone humide prairiale
Wetlands are threatened by climate change and the anthropization of natural environments. Satellite remote sensing is useful for environmental monitoring at large areas. However, when it comes to the study of hydrological dynamics, a significant temporal resolution is essential. The latter is difficult to reach with optical satellite imagery because of the cloud cover that masks the ground. Radar sensors are well suited to the characterization of hydrological dynamics thanks to the sensitivity of their measurements in the presence of water, whatever the vegetation in place. As a result, all Synthetic Aperture Radar (SAR) acquisitions are available, both day and night, regardless of cloud cover.Satellite radar remote sensing has gone through a revolution with the launch of the Sentinel-1A satellite, followed by its twins Sentinel-1B by the European Space Agency as part of the Copernicus program in 2014. These sensors acquire C-band data (λ = 5.6 cm) on a regular basis on Europe and their distribution is free for all users. Their temporal frequency initially of 12 days has decreased to 6 days from the end of 2016. This work aims at evaluating the potential of these data with high temporal resolution for the monitoring of water bodies and wetlands.The first part of this thesis focuses on water bodies mapping. We found confusion in the C-band radar response between water surfaces and that of some bare soils. We showed that the winter period is the least ambiguous and that the VH polarization is the most suitable for the mapping of water surfaces. Four methods of water detection have been compared. It appears that the use of unsupervised methods without a priori data is not conceivable and that the methods taking into account the spatial neighborhood give better results. Temporal filtering has been developed and has improved detection and avoided confusion between bare soil and permanent water surfaces. Water surfaces of more than 0.5 ha are more than 80% likely to be detected.A second part of this thesis is devoted to the monitoring of wet grasslands by radar remote sensing. The use of fully polarimetric data has shown that the VV/VH partial polarimetry configuration available on the Sentinel-1 sensor is able to characterize the prairial floods with or without vegetation. A method taking into account the temporal neighborhood allowed to process a series of 14 Sentinel-1 images to obtain 14 flood maps. The accuracy of floods maps at the intra-parcel scale has been estimated, it appears that if the precision is relatively good (80%), but the recall is rather low (40%). This method allow to establish intra- and inter-annual monitoring.This thesis has shown the potential of high temporal resolution radar images for the mapping of the water surfaces and for the monitoring of a wetland meadow

碩士
國立高雄師範大學
電子工程學系
101
In this thesis, the purpose of quasi-self-complementary structure antenna design mainly for impedance bandwidth can cover the 3.1~10.6 GHz for Ultra-wideband and 2.4/5.2/5.8 GHz triple-band for wireless LAN. We proposed three different antenna structure designs to analyze and discuss. Firstly, compact self-complementary antenna for ultra-wideband applications by adjusting geometry parameter can easily control bandwidth operation. Secondly, compact self-complementary Antenna with Band-Notch for WLAN applications by adjusting metal rectangular ground can control band-notch frequency for WLAN applications. Lastly, a pie-shaped self-complementary antenna for WLAN applications by adjusting slot Pie-shaped patch angle, can control band-notch frequency to WLAN applications. The above three antenna designs can cover ultra-wideband or wireless LAN system operation, with lower costs, simple fabrication and small size advantages.

碩士
國立彰化師範大學
電信工程學研究所
105
The objective of this thesis is to study and design balanced filtering antennas. The first circuit proposed in this research is a balanced band-notched ultra-wideband (UWB) filtering slot antenna with high gain. The high gain is achieved by deploying two identical open-ended T-shaped slot radiators in a back-to-back fashion. These two slot radiators are fed differentially by differential-mode (DM) signals output from a balanced band-notched UWB bandpass filter (BPF) constructed using a stepped-impedance slotline resonator. A DM notched band for blocking the 5-GHz WLAN band signals is generated by symmetrically placing a pair of microstrip resonators and a pair of slotline segments alongside the stepped-impedance slotline resonator. As compared with its standalone slot antenna counterpart, the DM passband selectivity and upper stopband rejection of the proposed balanced filtering UWB slot antenna have been improved, and very good common-mode (CM) suppression has been achieved. The second circuit proposed is the balanced quasi-self-complementary circularly polarized (CP) wideband filtering antenna. It is well known that the electric fields and the magnetic fields of the two complementary radiating elements are orthogonal to each other. Thus by carefully designing the differential feedlines to have a phase difference of 90 degrees, the designed balanced antenna can achieve the CP characteristic. In addition, two λ/2 microstrip lines with shared sections are connected between the two feedlines. When in CM operation, the λ/2 microstrip line sections work as two shunt λ/4 open stubs to produce two adjacent transmission zeros for suppressing CM signals within a quite-wide band. Also, with fine tuning of the perturbation structure embedded in the patch (slot), the 3-dB axial ratio (AR) bandwidth of the proposed filtering CP antenna can successfully cover the differential operating band to achieve wideband CP operation. In the third proposed circuit, only a single radiating element is used and no phase delay line is needed to implement the balanced CP filtering antenna. The idea of this design is to place the two differential feedlines with equal length perpendicularly in the antenna and carefully locating the two feedlines to form a 90 degrees phase difference. At the front end of the antenna, a balanced BPF is added to improve the passband selectivity and to provide good CM rejection. The result shows that the DM passband and the axial ratio can effectively enclose the desired 2.45-GHz WLAN band, and the designed balanced CP filtering antenna has very high CM rejection and good DM performance. The proposed balanced filtering antennas can find practical applications in UWB and WLAN communication systems. The design approaches can serve as useful reference for researchers working in this specialized area.

碩士
清雲科技大學
電機工程所
99
In this thesis, two loop antenna, used in UHF band (470MHz ~ 860MHz) radio and television digital microstrip antenna. In the design of architecture, there is the use of coplanar waveguide feed and complementary step resonator structure and the side ring to do with. Among the coplanar waveguide feed is designed for 50 ohm microstrip line in order to connect the ring structure and 50 ohm SMA connectors; step resonator is produced for the resonant response characteristics, the resonant frequency response to generate multiple role of broadband. In the spectrum, and in digital broadcast TV bands and the return loss is less than-10dB under the condition of a bandwidth of greater than 45% of the respondents. In-field analysis, the normalization of xz section and yz after radiation pattern graph profile, which xz section pattern diagram, showing a similar dipole antenna radiation pattern; in the yz section of the pattern graph, showing a similar pattern in all isotropic characteristics, from the simulated and measured results are worth knowing consistent.

碩士
國立高雄師範大學
電子工程學系
99
In this thesis, designs of ultra-wideband self-complementary antenna with band-rejection characteristics are presented. In the first chapter, we describe the self-complementary antenna for maximum impedance bandwidth of the physical properties. In the second, third, four chapters, three different techniques are proposed for band-rejection characteristics. In order to overcome the interference of exiting WLAN systems, direct changes in the antenna structure, can replace filter circuit, with lower costs, simple fabrication and small size advantages.

碩士
逢甲大學
電機工程所
97
Novel fractal antennas constructed with the Hilbert-curve and the self-complementary configuration are proposed for WLAN dual-band applications. The main aim of this thesis is to merge the monopole/dipole antennas and the self-complementary antenna in order to obtain a good performance of compact, dual-band and circular polarization. First, the self-complementary Hilbert-curve monopole antenna is constructed on a substrate with unbalance structure. Second, the self-complementary Hilbert-curve dipole antenna is depicted on a substrate with balanced configuration. And both exhibit the desired bands of 2.4 GHz and 5.2 GHz. The circular polarizations for dual-band are demonstrated with AR spectrum and electromagnetic characteristics. Results included with frequency responses, radiation patterns, current distributions and electric field intensities are presented and discussed.

The industry of wireless digital communications has matured since the 1970s with the introduction of cellular technology, to the present rollout of fourth generation infrastructure. The discovery and refining of technology such as orthogonal frequency division multiplexing (OFDM), code division multiple access (CDMA) and later multiple-input multiple-output (MIMO) techniques has set the stage for the current and future high capacity broadband wireless cellular networks. A number of organisations have developed standards for wireless communication technologies, most notably the Third Generation Partnership Project with the Long Term Evolution series of standards and the Institute of Electrical and Electronics Engineers (IEEE) with its IEEE 802 series of standards. This work aims to contribute to the afore mentioned field of research by amalgamating three key technologies into a wireless communication system. The methodology adopted has centred on orthogonality with the utilisation of OFDM, CDMA employing completely orthogonal complementary codes and MIMO techniques. OFDM provides a reduced complexity means for managing multipath environments by taking advantage of the fast Fourier transform (FFT) algorithm for modulation and demodulation. Furthermore the cyclic rotation scheme applied to the orthogonal complete complementary codes allows the use of spread spectrum technology without the inherent rate loss while providing multiple access. The recent advances in multiple antenna communication technology have led to the development of two branches in the field. The first of these was the introduction of the spatial multiplexing concept which increases the system capacity and the second was the development of many diversity achieving spatial coding techniques. Of the diversity achieving techniques orthogonal space-time block codes (OSTBC) are most notable due to their linear detectability. The performance of two communication systems has been evaluated through simulation. Both employ the multi carrier CDMA based on the cyclically rotated complete complementary codes however the fundamental difference between them is the spatial coding. Spatial multiplexing and OSTBCs have been utilised with a matrix algebraic framework description unifying both. The spatial multiplexed signals are detected with a non-linear sphere decoder and the OSTBC data is detected linearly. The results have shown that the systems achieve the expected diversity orders in flat fading conditions. The OSTBC system achieves added gains in multipath conditions due to the spread spectrum coding. The codes provide multiple access as well as extract added multipath diversity that would otherwise be unavailable. Interestingly, both systems were unaffected by Doppler since perfect channel state information was assumed and the spreading was performed in frequency domain.
Dissertation (MEng)--University of Pretoria, 2014.
lk2014
Electrical, Electronic and Computer Engineering
MEng
Unrestricted

In the past decade, artificial materials have attracted considerable attention as potential solutions to meet the demands of modern microwave technology for simultaneously achieving component minimization and higher performance in mobile communications, medical, and optoelectronics applications. To realize this potential, more research on metamaterials is needed. In this dissertation, new bandpass filter and diplexer as microwave metamaterial applications have been developed. Unlike the conventional complementary split ring (CSRR) filters, coupled lines are used to provide larger coupling capacitance, resulting in better bandpass characteristics with two CSRRs only. The modified bandpass filters are used to deisgn a compact diplexer. A new CSRR antenna fed by coplanar waveguide has also been developed as another metamaterial application. The rectangular shape CSRRs antenna achieves dual band frequency properties without any special matching network. The higher resonant frequency is dominantly determined by the outer slot ring, while the lower resonant frequency is generated by the coupling between two CSRRs. The proposed antenna achieves about 35 percent size reduction, compared with the conventional slot antennas at the low resonant frequencies. As a future alternative energy solution, space solar power transmission and wireless power transmission have received much attention. The design of efficient rectifying antennas called rectennas is very critical in the wireless power transmission system. The conventional method to obtain long distance range and high output power is to use a large antenna array in rectenna design. However, the use of array antennas has several problems: the relatively high loss of the array feed networks, difficultiy in feeding network design, and antenna radiator coupling that degrades rectenna array performance. In this dissertation, to overcome the above problems, a reflectarray is used to build a rectenna system. The spatial feeding method of the reflectarray eliminates the energy loss and design complexity of a feeding network. A high gain rectifying antenna has been developed and located at the focal point of the reflectarray to receive the reflected RF singals and genterate DC power. The technologies are very useful for high power wireless power transmission applications.

碩士
國立彰化師範大學
電信工程學研究所
106
The objective of this thesis is to study and design differentially-fed circularly-polarized (CP) antennas. The research topics of interest include CP antennas designed using differentially-fed quasi-self-complementary (QSC) structure and stub- or slit-loaded slot. The first circuit proposed in this research is a novel design of a common-mode suppressed differentially-fed CP antenna using a QSC structure. The antenna radiating element consists of a semicircular-ring radiating patch and its complementary magnetic counterpart. The design idea for producing CP radiation is based on field orthogonality of the QSC structure. For better impedance matching, a fan-shaped notch (stub) around the feeding position was cut from (implemented in) the semicircular radiating patch (slot). In addition, to improve the axial ratio, a QSC semielliptical structure is embedded in the central area of the antenna. It shows that by properly tuning the dimensions of the embedded QSC semielliptical structure, better axial ratio performance and radiation patterns can be obtained. The second circuit proposed in this thesis is a differential-opposite-fed CP antenna. The CP antenna consists of a pair of opposite-fed C-shaped radiating patches and a stub-loaded corner-truncated rectangular slot. Since an opposite feeding configuration is adopted and the geometry of the CP antenna is designed anti-symmetrical with respect to the plane of symmetry, very good differential-mode (DM) performance can be obtained. On the other hand, the radiations by the corresponding parts of the anti-symmetrical CP antenna structure will be destructive when in common-mode (CM) operation. This results in high CM suppression without the need of a preceding CM-rejection bandpass filter. Also, good DM axial ratio is achieved by tuning the protruded stub length and the coupling length of the C-shaped radiating patches. This third circuit presented is a differential-opposite-CPW-fed CP antenna. The design idea is similar to that for the antenna of the second circuit. The CP antenna is composed of a slit loaded rectangular slot and two oppositely-fed L-shaped radiation patches. As for the second circuit, the whole antenna circuit is arranged in a rotationally symmetric manner to produce the additive orthogonal fields under differential excitation and destructive radiation fields when in CM operation to achieve good common mode rejection. As is seen, the radiation characteristic of this differential-opposite-CPW-fed CP antenna mostly resembles that of the second one. The result shows that the DM CP bandwidth can effectively cover the desired 2.45-GHz WLAN operating band. All the differentially-fed CP antennas designed in this thesis exhibit good DM performance and high CM rejection. Good axial ratio response and radiation patterns are also observed. They can find practical applications in WLAN communication systems and the design approaches can serve as a useful reference for researchers working in this area.