This thesis presents a solution to the problem of receiving a signal in the shadow and fringe areas. Theoretical and experimental investigation of the field behind an obstacle in a line of sight transmission path for UHF / microwave signals has resulted in a new approach to the analysis of electromagnetic fields in the shadow of an obstacle. Analysis using this approach showed the field to consist of varying amplitude and phase distribution. Additional analysis predicted an increase in received signal could be achieved if correlation between the field and antenna structure could be obtained. This was accomplished with a new antenna design. The thesis presents experimental and photographic evidence to support the theory. A novel technique involving the matching of the antenna structure to the field distribution, resulted in an increase of received signal in the diffracted field of up to 4 dB.

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

Recent years have seen a growing interest in a new kind of periodic structures called ``metamaterials'. These new artificial materials exhibit many new appealing properties, not found in nature, and open many new possibilities in the domain of antenna design. This thesis describes efficient numerical tools and methods for the analysis of infinite and finite periodic structures. A numerical simulation code based on the Method of Moments has been developed for the study of both large phased arrays and periodic metamaterials made of metal and/or dielectrics. It is shown how fast infinite-array simulations can be used in a first instance to approximately describe the fields radiated by large antenna arrays or compute transmission and reflection properties of metamaterials. These infinite-array simulations rely on efficient computation schemes of the doubly periodic Green’s function and of its gradient. A technique based on eigenmode analysis is also described, that allows to efficiently compute the dispersion curves of periodic structures. Accounting for the finiteness of real structures is possible in good approximation thanks to a finite-by-infinite array approach. Moreover, the excitation of large finite periodic structures by a single (non periodic) source can be studied by using a combination of the Array Scanning Method with a windowing technique. All these techniques were validated numerically on several examples and it is finally shown how they can be combined to design high gain antennas, based on metamaterial superstrates excited by a slotted waveguide. The proposed design method relies on the separation of the whole structure in two different problems. An interior problem is used to optimize the input impedance of the antenna, while the radiation pattern can be optimized in the exterior problem.

Bibliography: p. 41.

One of the primary sources of inefficiency in today's wireless networks is the half-duplex constraint - the assumption that nodes cannot transmit and receive simultaneously in the same band. The reason for this constraint and the hurdle to full-duplex operation is self-interference: a node's transmit signal appears at its own receiver with very high power, desensitizing the receiver electronics and precluding the reception of a packet from a distant node. Recent research has demonstrated that full-duplex can indeed be feasible by employing a combination of analog and digital self-interference cancellation mechanisms. However, two glaring limitations remain. The first is that the full-duplex state-of-the-art requires at least two antennas and extra RF resources that space-constrained mobile devices may not be able to accommodate. The second limitation is range: current full-duplex demonstrations have been for ranges less than 10~m. At longer distances nodes must transmit with higher power to overcome path loss, and the power differential between the self-interference and the signal-of-interest becomes more that the current cancellation mechanisms can handle. We therefore present engineering solutions for answering the following driving questions: (a) can we leverage full-duplex in a network consisting mostly of half-duplex mobiles? and (b) can we extend the range of full-duplex by achieving self-interference suppression sufficient for full-duplex to outperform half-duplex at ranges exceeding 100 m? In answer to the first question, we propose moving the burden of full-duplexing solely to access points (APs), enabling the AP to boost network throughput by receiving an uplink signal from one half-duplex mobile, while simultaneously transmitting a downlink signal to another half-duplex mobile in the same band. In answer to the second question we propose an AP antenna architecture that uses a careful combination of three mechanisms for passive suppression of self-interference: directional isolation, absorptive shielding, and cross-polarization. Results from a 20 MHz OFDM prototype demonstrate that the proposed AP architecture can achieve 90+ dB total self-interference suppression, enabling >50% uplink rate gains over half-duplex for ranges up to 150 m.

An antenna for a wireless sensor network for trains is designed and built. The network will monitor temperature and vibrations of the wheel bearings on the train wagons. Doing this will allow for an earlier detection of damaged wheels, which will ease planning of maintenance and reduce wear on the rails considerably. The requirement of the system is that it is to be installed without any cables attached to the sensor nodes. This calls for wireless communication, and that for that antennas are needed.A train is a difficult environment to transmit electromagnetic (EM) waves in. It is full of metal and EM-waves cannot pass through a conducting material. Having much metal in its vicinity also affects the function of the antenna. This needs to be taken into consideration when making the design.The constructed antenna is a small dual-layer patch antenna. Dual layer means that it is constructed out of two sheets known as substrates of isolating material with different characteristics. The lower one of these substrates is made in such a way that integration with a circuit board is possible. Such integration would reduce the production cost considerably. The antenna is designed for direct placement on a conducting surface. This surface could be part of the train. It uses the surrounding metal as a ground plane in order to reduce its size. The result is a small patch antenna with good radiation qualities in metallic surroundings. The longest side is 18.35 mm, equaling 14.9 % of the wavelength that the antenna is designed for. / WISENET

Future wireless networks will be required to transmit real-time multimedia data reliably with high speed and low latency. This demands new approaches to the design and analysis of wireless networks. In this context, multiple antenna architectures are a promising solution which provide wireless systems with a high degree of functionality, adaptability, capacity, and robustness. However, efficient use of these systems is possible only by solving a number of critical problems. In this dissertation, we focus on coding and information theoretic aspects of multiple antenna systems. Knowledge in these areas provides us with guidelines into analysis and design of systems, reveals inherent limitations, pinpoints problems and opportunities for improvement, and also allows for rigorous argument and justification of observations. We present novel results on multiple antenna communication systems with both theoretical and practical impacts. In the area of coding theory, performance limits and error bounds for space-time codes will be discussed, along with guidelines for systematic design of space-time codes in the presence of the channel correlation profile. In the area of information theory, a unified approach to the capacity analysis of multiple antenna channels will be discussed. We also present a novel partial ordering relation on fading channels that is helpful in information theoretic analysis of compound and non-stationary channels. The results of the dissertation can be generalized to multiple-user channels. This could lead to a solid understanding of fundamental limits of wireless systems and opportunities for opening new trends and paradigms for future generations of wireless networks.

A phased array antenna differs from a conventional antenna, such as a dish antenna, in that it coherently adds radiation from multiple radiating elements instead of mechanical positioning to direct RF energy. When transmitting and receiving information from a source while in motion, a phased array antenna can continuously adjust its signal to focus on the source. New antenna designs focus on integrating phased array antennas into the structure of the antenna platform, as advanced antenna platforms require the antenna to take up less and less real estate. With further development of phased array antennas, new designs become increasingly complex. The manufacturing techniques to facilitate the integration of complex antenna designs into the structure of an antenna platform must be developed, as traditional manufacturing operations, such as injection molding, machining and bulk deformation processes, are not well suited to create the small details and complex three dimensional lattice designs of the antennas. Innovative solutions need to be developed that allow the manufacture of complex antennas, thereby enabling testing to be performed on actual devices. The results from testing physical models can buttress analytical models and lead to better antenna designs. This work developed and studied suitable methods for manufacturing three-dimensional, structurally-integrated antennas.

In recent years, the miniaturization of cell phones and computers has led to a requirement for antennas to be small and lightweight. Antennas, desired to operate in the WLAN frequency range, often possess physical sizes that are too large for integration with radio-frequency (RF) devices. When integrating antennas into three-dimensional (3D) system-on-package (SOP) transceivers, the maintenance of a compact size also provides isolation from other devices, hence, surface wave propagation or high dielectric constant materials such as low temperature cofired ceramics (LTCC) does not affect nearby components of the transceiver such as filters, baluns, and other embedded passives. Therefore, the application of design methods is necessary for realizing compact antennas in the wireless community that can be integrated to RF packages. Furthermore, it is essential that these compact antennas maintain acceptable performance characteristics, such as impedance bandwidth, low cross-polarization, and high efficiency. In addition, the analysis of circuit modeling techniques that could be used to obtain a better understanding of the physical phenomena of the antenna is quite necessary as modules become more and more complex. Based on these requirements, the focus of this research is to improve the design of compact antennas for wireless communications, wireless local area networks (WLAN), and millimeter-wave applications by using time-domain electromagnetic and circuit modeling techniques and optimizations. These compact antenna designs are applied to practical wireless communications systems such as global system of mobile communications (GSM), Bluetooth Industrial-Scientific-Medical (ISM) devices, IEEE802.11a WLAN, and Local Multipoint Distribution Systems (LMDS) applications. Parametric analyses are conducted to study critical parameters that may affect the antenna designs. Moreover, optimizations are performed to optimize the structures, and measured results are presented to validate design techniques.

Dielectric resonator antennas(DRAs) offer some attractive characteristics over conventional microstrip antennas, such as small size, low profile, light weight, ease of excitation, and high radiation efficiency at higher frequency bands. Since DRAs attract more and more attention, theoretical analysis have been insufficient to simulate various configurations of dielectric resonator antennas. Therefore some researchers introduce numerical methods to analyze DRAs, such as Finite Difference Time Domain (FDTD) method, Method of Moment (MoM), Finite Element Method (FEM). In this author, we apply two kinds of methods, including FDTD and MoM, to analysis DRA and compare the results applied these two methods. Then we simulate various configurations of dielectric resonator antennas using FDTD method. About designing the DRA construction, in this author we applied an equivalent approach to solve approximate dimensions of DRAs, and then we obtain accurate dimensions using FDTD method. In this author¡Aa DRA work at 5.8GHz have been proposed, then we using a L-shaped patch to increase impedance bandwidth. Above all, we hope to built a fast and accurate procedure to solve the resonant frequency, bandwidth, and far field pattern of DRAs. And to supply the engineer to reduce time consume in design DRAs.