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The design of antenna arrays involves, amongst others, the selection of the array elements and geometry, as well as the element excitations. The feeding network to obtain the desired excitations can become quite complex, and hence expensive. One possible alternative would be to make use of micros trip wire-grid antenna arrays. These arrays are composed of staggered interconnected rectangular loops of dimensions a half¬wavelength by a wavelength (in the presence of the dielectric). It is because the short sides are considered to be discrete elements fed via micros trip transmission lines, that these antennas are viewed as arrays. While considerable success has been achieved in the design of these antennas, published work has been either of an entirely experimental nature or based on approximate (albeit clever) network models which do not allow for fine control of the array element excitations or off-centre-frequency computations generally. It is the purpose of this thesis to perform an almost rigorous numerical analysis of these arrays in order to accurately predict their element excitations. Models used to study microstrip antennas range from simplified ones, such as transmission-line models up to more sophisticated and accurate integral-equation models. The mixed-potential integral equation formulation is one of these accurate models which allows for the analysis of arbitrarily shaped microstrip antennas with any combination of frequency and dielectric thickness. The model treats the antenna as a single entity so that physical effects such as radiation, surface waves, mutual coupling and losses are automatically included. According to this formulation, the microstrip antenna is modelled by an integral equation which is solved using the method of moments. By far the most demanding part of the integral equation analysis is its actual numerical implementation. For this reason a complete description of the numerical implementation of the formulation is given in this thesis. To verify the accuracy of the implementation, rectangular microstrip patch antennas were analysed and surface current distributions were shown to compare favourably with published results. The formulation is then applied to the analysis of micros trip wire-grid antenna arrays which makes it possible to accurately predict surface current distributions on these arrays. Radiation patterns are determined directly from computed current distributions in the presence of the dielectric substrate and groundplane, and are essentially exact except for finite groundplane effects. To verify theoretically predicted results for wire-grid antenna arrays, several arrays were fabricated and actual radiation patterns were measured. Good correspondence between measured and predicted co-polar radiation patterns was found, while the overall cross¬polarization behaviour in cases with large groundplanes could also be predicted. The fact that numerical experimentation can be performed on wire-grid antenna arrays to examine element excitations, means that it is now possible to carefully design for some desired aperture distribution. / Dissertation (MEng)--University of Pretoria, 2010. / Electrical, Electronic and Computer Engineering / unrestricted

Acquisition of ultra-wideband signals by means of array antennas requires essentially frequency-independent radiation characteristics over the entire bandwidth of the signal in order to avoid distortions. Factors contributing to bandwidth limitation of arrays include array factor, radiation characteristics of the array element, and inter-element mutual coupling. Strictly speaking, distortion-free transmission or reception of ultra-wideband signals can be maintained if the magnitude of the radiated field of the array remains constant while its phase varies linearly with frequency over the bandwidth of interest. The existing wideband-array synthesis methods do not account for all factors affecting the array bandwidth and are often limited to considering the array factor and not the total field of the array in the synthesis process. The goal of this study is to present an ultra-wideband array synthesis technique taking into account all frequency-dependent properties, including array total pattern, phase of the total radiated field, element field, element input impedance, and inter-element mutual coupling. The proposed array synthesis technique is based on the utilization of frequency-adaptive element excitations in conjunction with expressing the total radiated field of the array as a complex Fourier series. Using the proposed method, element excitation currents required for achieving a desired radiation pattern, while compensating for frequency variations of the element radiation characteristics and the inter-element mutual coupling, are calculated. An important consideration in the proposed ultra-wideband array design is that the "phase bandwidth", defined as the frequency range over which the phase of the total radiated field of the array varies linearly with frequency, is taken into account as a design requirement in the synthesis process. Design examples of linear arrays with desired radiation patterns that are expected to remain unchanged over the bandwidth of interest are presented and simulated. Two example arrays, one with a wire dipole as its element and another using an elliptically-shaped disc dipole as the element are studied. Simulation results for far-field patterns, magnitude and phase characteristics, and other performance criteria such as side-lobe level and scanning range are presented. Synthesis of two-dimensional planar arrays is carried out by employing the formulations developed for linear arrays but generalized to accommodate the geometry of planar rectangular arrays. As example designs, planar arrays with wire dipoles and elliptical-shaped disc dipoles are studied. The simulation results indicate that synthesis of ultra-wideband arrays can be accomplished successfully using the technique presented in this work. The proposed technique is robust and comprehensive, nonetheless it is understood that the achieved performance of a synthesized array and how closely the desired performance is met also depends on some of the choices the array designer makes and other constraints, such as number of elements, type of element, size, and ultimately cost. / Ph. D.

Developements in next-generation advanced communication systems and devices have triggered multi-antenna systems for improved data throughput and transmission reliability. According to Shannon's theorem, to improve the channel capacity of a communication system, one method is to broaden the system bandwidth. Another method is to use the multiple-input-multiple-output (MIMO) technology. This technology uses multiple antennas at both transmitter and receiver to improve the channel capacity by several folds. Therefore, compact and broadband multi-antenna systems are very promising for future high-capacity wireless communication systems. / In parallel to advances in MIMO technologies, there is an irreversible trend that more and more communication protocols together with their respective antennas and radio transceivers are integrated into one compact unit. The radio systems of different protocols may work in very closely adjacent frequency bands or even overlapped bands. The coexistence of these multiple antennas has also become a concern from both industry and academic communities. / However, since the number of antenna elements is increasing in more and more compact devices, the physical limitation on inter-element spacing cannot be easily transcended, which will lead to destructive mutual coupling interference as well as pattern/spatial dependent correlation. In a multi-antenna system, the signals at all antenna ports are coded differently either to increase the packet rate or simply because that they belong to different radio transceivers. If unwanted signals are coupled to the ports, the signal-to-noise ratio will be deteriorated. Furthermore, the far-field patterns of closely spaced antennas are highly correlated and the signal envelope correlation will become significantly large. All these negative impacts will greatly diminish the channel capacity and the data throughput. Such drawbacks restrain the use of multiple antenna systems. It is therefore vital to develop a simple, broadband and effective decoupling technique for compact multiple antenna systems/arrays in advanced communication systems. / The major objectives of this thesis are (1) to innovate a new antenna decoupling technique called shunt type of coupled resonator decoupling networks (S-CRDNs) for wireless mobile terminal antennas; (2) to develop the synthesis theory and the design methodologies of the shunt type of CRDNs (S-CRDN) for various of antenna arrays; (3) to extend the theory and the design concept to dual band S-CRDNs, three port S-CRDNs and a LTCC S-CRDN module for mobile terminal applications; (4) to develop a cascaded type of coupled resonator decoupling networks (C-CRDN) for base station and wireless routers antennas; (5) to innovate a novel decoupling technique for multiple element antenna arrays with dummy antennas arrays; and more importantly, (6) to explore innovative applications with experimentally verified superiority. / Based on the characteristics of the coupled antennas, the synthesis theory of S-CRDNs starts from a set of required admittance polynomials, the targeted coupling matrix can be obtained from the polynomials analytically for a second-order S-CRDN. Possible coupling topologies of S-CRDNs include, but not limited to, a second-order all pole S-CRDN, a second-order S-CRDN with source-load coupling, a high-order S-CRDN network for dual band applications and a three port S-CRDN for three-element antenna arrays. Moreover, the concept of a “one-fit-all” S-CRDN module base on LTCC technology is also proposed and investigated, which makes an integrated S-CRDN module antenna independent as long as the frequency range matches. / The general theory of C-CRDN is developed in this thesis based on the circuit model of a 4-port coupled resonators network, which is proposed to solve the antenna decoupling problem between two base station antennas, to which a high level of isolation between two adjacent frequency bands is required, for the first time. This type of CRDN is particularly useful when one antenna transmitting very high power energy in a vicinity to a receiver antenna that works in an adjacent frequency band with very high sensitivity. / A decoupling technique with appropriately designed dummy elements and their passive complex loading is also proposed in this thesis. The technique employs the characteristics of non-radiating antenna elements (dummy elements). Multiple dummy elements can be introduced to alter the mutual coupling characteristic the radiating antennas in the original compact array. Therefore, this technique is more suitable for decoupling problem of an array with multiple elements. It is demonstrated that for a four-element compact array, four dummy elements are sufficient to decouple the four radiating elements in a broadband sense. Additionally, each radiating element can be independently matched. This decoupling technique can be extended to antenna arrays with a high number of radiating elements. / Finally, necessary and important figures of merit for benchmarking a multiple element antenna array are introduced. Prototypes of multi-antenna systems with and without using proposed decoupling techniques are fabricated, measured and compared. A large number of experimental results have demonstrated the superiority and the significance of the proposed decoupling techniques for compact antenna arrays of advanced wireless communication systems. / 下一代無線通訊系統與設備的飛速發展，極大的促進了多天線系統的開發與應用。多天線系統天生具有高數據吞吐率，并能夠確保傳輸的穩定性。根據香農定律，若想要提高一個系統的信道容量，要麼可以展寬系統帶寬，要麼可以適用多輸入多輸出（MIMO）系統。MIMO技術在發射端和接收端安置多個天線，以同時發送多路數據，大大提高了數據的吞吐率和信道容量。理想的狀態下，信道容量隨著收發天線的個數可以線性成倍增加。因此，新一代的小型化多天線系統正在成為未來發展的趨勢。 / 與此同時，現今無線通訊系統的發展趨勢越來越朝著小型化，集成化以及多功能化發展。這就意味著，越來越多的通信協議及其收發機和天線，將會集成到一個越來越小的終端設備上。另外由於頻譜資源的稀缺，這些共同工作的系統的頻帶越來越寬，頻帶之間的距離也越來越近。這些多天線的共存問題，也日益成為學術界和工業界關心的焦點問題。 / 但是，當終端的尺寸越來越小，而天線的個數越來越多的時候，天線之間的物理距離這個瓶頸是無法逾越的。如此受限的距離，不但造成了天線之間的相互干擾較大，也造成了他們方向圖和信道的強相關。在多天線系統中，各個天線處的信號編碼是不同的（包括提高數據速率和提高通信可靠性兩種不同的模式）。如果無用的信號耦合到了不該到的端口或者天線處，就會極大的影響信噪比和通信質量。另外，如果多天線的方向圖和信道是相關的話，信號的包絡相關性就會變得異常的大。這些都是嚴重影響多天線系統的性能的因素。因此，設計一種簡單的，寬帶的，有效的解耦技術，對於多天線系統是至關重要的。 / 本論文的主要目標是：（1）開發一種新的天線解耦技術，叫做並聯型耦合諧振腔解耦網絡，專門針對手機終端。（2）研究針對此解耦網絡的綜合設計手段，以針對不同的多天線陣列，都能有效的設計。（3）將此技術推廣到雙頻，多頻，多端口的多天線系統中。并研究利用低溫共燒陶瓷技術實現此類器件的小型化。（4）開發另一種級聯型耦合諧振腔解耦網絡，專門針對基站和路由器應用。（5）開發一種利用“假”天線進行解耦的新型技術。更重要的是（6）在實際使用場景中驗證所提出的各種解耦技術的有效性。 / 並聯型耦合諧振腔解耦網絡的綜合方法，需要受限根據耦合天線的特性和參數，得到一組電抗多項式，對於二階的網絡，所需要的耦合係數可以有這些多項式解析得到。實際上，並聯型耦合諧振腔解耦網絡的拓撲結構是多樣的，其中包括：兩階無交叉耦合型，兩階有交叉耦合及源負載耦合型，高階針對多頻的網絡以及三端口的網絡，專門針對三單元天線陣列。從並聯型耦合諧振腔解耦網絡，可以衍生出一種非常重要的基於低溫共燒陶瓷技術的“全能型”解耦網絡。這種網絡在頻率確定的情況下，可以適應各種不同的天線形式和耦合，非常適合在手機終端上廣泛採用。 / 本論文還討論了針對級聯型耦合諧振腔解耦網路的一般理論，以及其對應的電路模型和網絡參數。這種類型的網絡非常適合解決需要極高隔離度的基站天線解耦問題。這種網絡在本文中是業界首次提出的針對發射天線對領進頻帶接收機強幹擾的微波無緣網絡解決方案。 / 另外，一種採用“假”天線配合其電抗負載進行解耦的方法也將在文中提到。這種技術利用了並不輻射的“假”天線的寄生特性，通過引入若干不同空間排布的假天線陣，來解決原有天線陣的強互耦問題。這種方法的優越性是可以針對多種不同單元數和不同陣列排布的陣列。 / 最後，本文將會一一討論多種評估多天線系統性能指標的參數。包括隔離度，效率，包絡相關性，信道容量乃至吞吐率。作為比較，多種多天線系統，包括採用解耦網絡技術和不採用解耦網路技術的天線陣的各種性能參數，都在文中做了詳細比較。大量的實驗證明了採用解耦網絡的多天線系統的優越性。 / Zhao, Luyu. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2014. / Includes bibliographical references. / Abstracts also in Chinese. / Title from PDF title page (viewed on 26, October, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

by Fu Kar Kit. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 158-160). / Abstract also in Chinese. / Chapter Chapter 1: --- Introduction --- p.1 / Chapter Chapter 2: --- Background and Theories --- p.3 / Chapter 2.1 --- Background History --- p.3 / Chapter 2.2 --- Finite Difference Time Domain Method --- p.4 / Chapter 2.2.1 --- Basic Formulation --- p.4 / Chapter A ) --- Governing Equations --- p.4 / Chapter B ) --- Discretization of Differential Equations --- p.6 / Chapter C ) --- Numerical Stability --- p.7 / Chapter 2.2.2 --- Absorbing Boundary Condition ( PML - Bandlimited ) --- p.8 / Chapter A ) --- Berenger Perfectly Matched Layer --- p.8 / Chapter B ) --- "Theroy, Two-Dimensional TE Case" --- p.10 / Chapter B-1 ) --- Propagation of a Plane Wave in a PML Medium --- p.11 / Chapter B-2 ) --- Transmission of a Wave through PML-PML Interfaces --- p.15 / Chapter B-3 ) --- PML for the FD-TD technique in 2-D domain --- p.18 / Chapter C ) --- Extension to Three-Dimension Case --- p.22 / Chapter 2.2.3 --- Modeling of Source and Passive Lumped-Circuit --- p.25 / Chapter 2.2.4 --- Obtaining the frequency dependent parameters --- p.27 / Chapter 2.2.5 --- Time Domain Extrapolation --- p.29 / Chapter 2.2.6 --- Near-to-Far-Field Transformation --- p.33 / Chapter A ) --- FD-TD implementation of Near-to-Far-Field Transformation --- p.35 / Chapter B ) --- Numerical Techniques to compute the Antenna Directivity --- p.38 / Chapter 2.3 --- Transmission Line Circuit Theories --- p.40 / Chapter 2.3.1 --- Stripline --- p.43 / Chapter 2.3.2 --- Microstrip Line --- p.46 / Chapter 2.3.3 --- Quadrature 90° Hybrid --- p.50 / Chapter 2.3.4 --- Butler Matrices --- p.50 / Chapter A ) --- Types of hybrids --- p.54 / Chapter B ) --- Number of hybrids --- p.51 / Chapter C ) --- Number of fixed phase shifters --- p.51 / Chapter D ) --- Positions and magnitudes of fixed phase shifters --- p.51 / Chapter E ) --- Values of total phase shift at output ports and produced by input ports --- p.53 / Chapter 2.4 --- Antenna Theories --- p.54 / Chapter 2.4.1 --- Microstrip Patch Antenna --- p.54 / Chapter A ) --- Bandwidth Enhancement --- p.55 / Chapter B ) --- Antenna design methodology --- p.55 / Chapter B-1 ) --- Substrate selection --- p.55 / Chapter B-2 ) --- Rectangular element analysis and design --- p.56 / Chapter 1) --- Electromagnetically coupled patch --- p.57 / Chapter 2) --- Aperture coupled patch --- p.61 / Chapter 2.4.2 --- Array Antenna --- p.67 / Chapter Chapter 3: --- Butler Matrix Analysis and Design --- p.73 / Chapter 3.1 --- Circuit Topology --- p.73 / Chapter 3.1.1 --- Basic Operation of the 4x4 Butler Matrix --- p.74 / Chapter 3.2 --- Design Methodology and Circuit Characteristics --- p.75 / Chapter 3.2.1 --- 3 dB branch-line coupler --- p.76 / Chapter 3.2.2 --- 0 dB branch-line coupler --- p.79 / Chapter 3.2.3 --- 4x4 Butler matrix Beamforming network --- p.82 / Chapter Chapter 4: --- Multibeam Array Analysis and Design --- p.90 / Chapter 4.1 --- Antenna Architecture --- p.90 / Chapter 4.2 --- Antenna Design --- p.91 / Chapter 4.2.1 --- Antenna Choice --- p.91 / Chapter A ) --- Microstrip Dipole --- p.91 / Chapter B ) --- Rectangular Microstrip Patch --- p.91 / Chapter C ) --- Circular Patch --- p.92 / Chapter D ) --- Compact Patch --- p.93 / Chapter E ) --- Annular Resonators --- p.94 / Chapter F ) --- Antenna Choice of the 4x4 Butler Matrix Network --- p.94 / Chapter 4.2.2 --- Choice of Feeding and Matching Technique --- p.95 / Chapter 4.2.3 --- Basic Antenna Parameters and Measurement Technique --- p.95 / Chapter A ) --- Radiation Pattern --- p.95 / Chapter B ) --- Radiation Pattern Lobes --- p.96 / Chapter C ) --- Antenna Gain --- p.97 / Chapter D ) --- Input Impedance --- p.97 / Chapter E ) --- Bandwidth --- p.97 / Chapter 4.2.4 --- FDTD Characterization --- p.98 / Chapter 4.3 --- Multibeam Antenna Design and Optimization --- p.104 / Chapter 4.4 --- Stripline Fed - Multibeam Antenna --- p.107 / Chapter 4.4.1 --- Design Methodology of the Stripline 3 dB Hybrid --- p.109 / Chapter 4.4.2 --- Design Methodology of the Stripline 0 dB Hybrid --- p.111 / Chapter 4.4.3 --- Design Methodology of the Stripline 4x4 Butler Matrix Network --- p.113 / Chapter 4.4.4 --- Design Methodology of the Stripline Aperture Coupled Patch --- p.138 / Chapter 4.4.5 --- Design Methodology of the Stripline Multibeam Antenna --- p.142 / Chapter Chapter 5: --- Design Examples and Application of Multibeam Antenna --- p.150 / Chapter 5.1 --- Wireless Local Loop (WLL) System --- p.150 / Chapter Chapter 6: --- Conclusions and Recommendations for Future Work --- p.156 / Chapter 6.1 --- Conclusions --- p.156 / Chapter 6.2 --- Recommendations for Future Work --- p.157 / Bibliography --- p.158 / Publication List --- p.160

This is an investigation of the proposed ‘Square Kilometer Array’ (SKA) for the next generation radio telescope. A parallel plate system with a circular reflector has been investigated for SKA to achieve wideband performance and beam scanning ability, in particular the theoretical analysis of the fields in the parallel plate structure using a combination of Finite Difference Time Domain method and Physical Optics. This study builds on earlier work, explores the possible limits of extension and develops an analysis of the device, which will allow all possible configurations to be simulated. It is anticipated that the final scanning arrangement will consist of at least a double reflector system, possibly with some re-configurability, where the parallel plates will have two 180 degree bends with the output being some form of directly radiating aperture. Results were obtained for a Re-configurable Monopole, where diodes are used as switches to physically vary the length of the antenna element and hence increase the bandwidth of the antenna. Re-configurable reflectors were also investigated and Geometrical Optics was used for shaping a dual-reflector Cassegrain system for beam scanning. All of these methods have produced satisfactory practical and analytical results / Doctor of Philosophy (PhD) Electrical Engineering

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 109-118). Available also in a digital version from Dissertation Abstracts.

Thesis--Auburn University, 2009. / Abstract. Vita. Includes bibliographic references (p.49-51).