Thesis (MScIng)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: The quadrifilar helix antenna has frequently been employed to provide the wide angle, circularly polarized radiation pattern which is preferable for mobile satellite communications. A detailed study of this antenna and its varieties is presented. When used as an element in wide angle scanning arrays for aeronautical satellite tracking applications, the additional requirement of a low profile with light weight applies. This further complicates the realization of good circular polarization close to the horizon. A top disk is incorporated into various antenna structures in an effort to improve the radiation performance when used within a closely spaced array while reducing the height of the radiating element. The array performance of these elements are investigated which hints at a supported traveling mode aiding the ability to accomplish the wide angle beam steering. Subsequent study of leakywave antennas initiated the study and implementation of leaky-wave structures in phased arrays of quadrifilar helix elements. / AFRIKAANSE OPSOMMING: Die vierledige heliksantenna word dikwels gebruik vir toepassings wat ’n wye, sirkulêr gepolariseerde stralingspatroon benodig. ’n Verskeidenheid van hierdie antennas is noukeurig bestudeer en hul toepaslikheid vir mobiele sattelietkommunikasie ondersoek. Wanneer hierdie antennas in fase gestuurde skikkings gebruik word, word dit ook vereis dat die eenhede liggewig is met ’n lae profiel. Dit bemoeilik die verkryging van goeie sirkulêre polarisasie naby die horison aansienlik. In ’n poging om die wyehoek straling met kort antennas te verbeter, is ’n oorhoofse skyf tot verskillende heliksstrukture toegevoeg. In nou gespasieerde skikkings maak hierdie skywe ’n positiewe bydrae to wyehoekstralingeienskappe. Die invloed van lekmodusse wat binne die struktuur voortplant is ondersoek en gebruik in skikkings waarvan die bundel naby aan die horison gestuur word.

Approved for public release, distribution is unlimited / This thesis examines a circular adaptive antenna array used at the mobile station for a typical Direct Sequence Code Division Multiple Access (DS-CDMA) cellular mobile communications system. The primary objective is to reduce co-channel interference of a wideband CDMA cellular network under a multi-path fading environment. We analyzed the performance of a randomly positioned mobile terminal with a randomly orientated adaptive antenna array in the forward channel (base-station to mobile) of a multi-cell DS-CDMA system and established four performance boundaries. A single complex circular adaptive weight in each element channel of a circular adaptive array sufficiently processes narrowband signals. However, in order to process broadband signals, a tapped-delay line (transveral filter) is required. This tapped-delay line is employed because it can adjust the frequency dependent amplitude and phase. The performance of a DS-CDMA cellular system with a mobile terminal equipped with a circular array and a tapped-delay line is analyzed. It has been demonstrated that the optimization process has been extremely computationally expensive and hence minimum taps should be used for practical considerations. The results illustrated that, in general, for a four-element circular array system, a two tapped-delay line would be sufficient to equalize the broadband signal while providing a similar performance level to that of a narrow-band adaptive array system. / http://hdl.handle.net/10945/1080 / Major, Republic of Singapore Air Force

A dissertation submitted to the faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of science in Engineering Johannesburg 1991 / This dissertation discusses the interaction between shipboard antennas and their environment. The emphasis is on the Use of the Method of Moments to calculate the currents on the structure of the ship. These currents are induced by the antennas mounted on the structure of the ship. The parameters (such as grid spacing and wire radius) to use in creating a wire grid model of the ship is investigated and recommended values given. A sample ship is analyzed and the results obtained compared with measurements done in an unechoic chamber.

However, applying directional antennas to wireless networks can also cause new collisions, such as the new hidden terminal problem and the deafness problem. We study the challenges in the MAC layer design with directional antennas and present the state of the art of current MAC protocols with directional antennas. Then, we propose a novel collision avoidance scheme in terms of BT-DMAC (Busy-Tone based Directional Medium Access Control) to address the new collisions with directional antennas. Both the analytical and simulation results show that transmitting busy tones on a different channel can effectively reduce the hidden nodes and mitigate the deafness problem. Thus, integrating multiple channels with directional antennas can bring numerous benefits. Furthermore, we also explore some techniques in the MAC layer design with directional antennas. Some useful insights are also given. / The capacity of wireless networks are mainly affected by two key factors: the interference among concurrent transmissions and the number of simultaneous transmissions on a single interface. Recent studies have found that, using multiple channels can separate concurrent transmissions and significantly improve network throughput. However, those studies only consider wireless nodes that are only equipped with omni-directional antennas, which cause high collisions. On the other hand, some researchers have found that directional antennas bring more benefits such as the reduced interference and the increased spatial reuse compared with omni-directional antennas. But, they only focused on a single-channel network which only allows finite concurrent transmissions. In this thesis, we propose a novel network architecture, in terms of multi-channel networks using multiple directional antennas ( MC-MDA), which integrates the two technologies of multiple channels and directional antennas together and potentially brings more benefits. / We study the capacity of MC-MDA networks and explore the benefits of such networks. We have found that using directional antennas in multi-channel networks can greatly increase the network capacity. Furthermore, such networks require fewer channels than multi-channels with omni-directional antennas. More specifically, we study the channel assignment problem of such MC-MDA networks. Our results indicate that using directional antennas in wireless networks can significantly reduce the required number of channels. Directional antennas have a better spectrum reuse than omni-directional antennas. / Dai, Hongning. / Adviser: Kam-Wing Ng. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3596. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 173-183). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Yim, Ho Yan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (leaves 125-128). / Abstracts in English and Chinese. / Abstract --- p.ii / 論文摘要 --- p.iv / Acknowledgement --- p.vi / Table of Content --- p.vii / List of Figures --- p.x / List of Tables --- p.xiv / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Filter --- p.3 / Chapter 1.2 --- Antenna --- p.4 / Chapter 1.3 --- Outline of the Thesis --- p.6 / Chapter Chapter 2 --- Basic Theories in Filter and Patch Antenna Design --- p.7 / Chapter 2.1 --- Microwave Filter Design --- p.7 / Chapter 2.1.1 --- Transfer Functions --- p.8 / Chapter 2.1.2 --- Lowpass Prototype Filters and Elements --- p.14 / Chapter 2.1.3 --- Filter Transformations --- p.18 / Chapter 2.1.4 --- Admittance Inverter --- p.21 / Chapter 2.2 --- Antenna Concepts --- p.23 / Chapter 2.2.1 --- Microstrip Antenna --- p.23 / Chapter 2.2.2 --- Patch Antenna Design --- p.24 / Chapter 2.2.3 --- Polarization --- p.28 / Chapter Chapter 3 --- Review of Conventional Dual-band Filter Designs --- p.33 / Chapter 3.1 --- Bandstop / bandpass Filters in a Cascade Connection --- p.33 / Chapter 3.2 --- Stepped Impedance Resonator --- p.34 / Chapter 3.3 --- Tunable Transmission Zero for Spurious Responses Suppression --- p.36 / Chapter 3.4 --- Comparison --- p.38 / Chapter Chapter 4 --- Novel Dual-band Filter Design with Equal Bandwidth --- p.39 / Chapter 4.1 --- Introduction --- p.39 / Chapter 4.2 --- Frequency Behavior of Shunt Stubs --- p.39 / Chapter 4.3 --- Dual-band Resonator with Paralleled Stubs --- p.42 / Chapter 4.4 --- Dual-band Admittance Inverter --- p.47 / Chapter 4.5 --- Dual-band Filter Realization --- p.51 / Chapter 4.5.1 --- Simulation Examples --- p.54 / Chapter 4.5.2 --- Comparison of Simulation results --- p.60 / Chapter 4.5.3 --- Experimental Results --- p.64 / Chapter Chapter 5 --- Novel Dual-band Filter Design with Unequal Bandwidth --- p.70 / Chapter 5.1 --- Introduction --- p.70 / Chapter 5.2 --- Dual-band Resonator using Step-Impedance Line --- p.70 / Chapter 5.3 --- Dual-band Admittance Inverter --- p.74 / Chapter 5.4 --- Dual-band Filter Realization --- p.75 / Chapter 5.4.1 --- Comparison of Simulation Results --- p.81 / Chapter 5.4.2 --- Experimental Results --- p.85 / Chapter Chapter 6 --- Review of Conventional CP Antenna Designs --- p.91 / Chapter 6.1 --- Degenerated Mode Patch --- p.91 / Chapter 6.2 --- CP Stacked Microstrip Patch Antenna Array --- p.92 / Chapter 6.3 --- Coplanar Waveguide-fed Slot Antenna --- p.93 / Chapter 6.4 --- Dual-band CP antenna fed by 2 different 90° hybrid couplers --- p.95 / Chapter Chapter 7 --- Novel New Dual-band CP Antenna Design --- p.96 / Chapter 7.1 --- Introduction --- p.96 / Chapter 7.2 --- Dual-band CP Patch Antenna --- p.96 / Chapter 7.2.1 --- Slotted Square Patch Antenna --- p.96 / Chapter 7.2.2 --- Slotted Cross Patch Antenna --- p.99 / Chapter 7.2.3 --- Simulation Results: Slotted Cross Patch Antenna --- p.101 / Chapter 7.3 --- Dual-band Quadrature Hybrid --- p.104 / Chapter 7.3.1 --- Simulation Results: Dual-band Hybrid Coupler --- p.107 / Chapter 7.4 --- Dual-band CP Antenna Realization --- p.113 / Chapter 7.4.1 --- Antenna Configuration --- p.113 / Chapter 7.4.2 --- Measurement Setup --- p.114 / Chapter 7.4.3 --- Experimental Results --- p.115 / Chapter Chapter 8 --- Conclusions and Recommendations for Future Work --- p.123 / Chapter 8.1 --- Filter --- p.123 / Chapter 8.2 --- Antenna --- p.123 / Chapter 8.3 --- Recommendations for future work --- p.124 / References --- p.125 / Author's Publications --- p.128 / Acronyms and Abbreviations --- p.129

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 153-156).

The explosive growth of the biosensors and health-related wearable monitoring devices has accentuated the need for miniaturized, high-efficiency conformal bio-modules that can operate over a wide range of frequencies, while they can be integrated in wearable and lightweight configurations. One of the major issue for the implementation of Wireless Body Area Networks (WBAN) is the very limited range of commonly used metal antennas. Due to the high dielectric constant between the metal antenna material (as well as the metal-based circuitry) and the mostly "ionized-water" human body parts, the near-field gets significantly disturbed, while local reflections due to the dielectric mismatch further shorten the operation range. Even wearable bracelet-like sensing devices have a very low range due to this reason. Thus, there are two major aspects that are going to be addressed in this Thesis: enhanced-range wearable antennas for wireless biosensors and compact "rugged-polarization" wireless sensor readers.

Thesis (Ph. D.)--University of Queensland, 2001. / Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 68-72). Also available in electronic version. Access restricted to campus users.