Doctor of Philosophy, The Ohio State University, 2022, Electrical and Computer Engineering

The antenna pattern is an essential part of the design of RF systems and affects the performance and capabilities for many applications in communications, radar, and sensing. There are many applications which require specified antenna patterns with specific directivity, beamwidth, and sidelobe level (SLL). Single-element antennas usually have simple and specific patterns which are difficult to be shaped to meet more complicated pattern requirements. For instance, the popular parabolic reflector antenna uses a reflector which can be shaped to produce a desired radiation pattern with high directivity. However, it has a large structure and can only produce single fixed-beam patterns. On the other hand, array antennas consist of multiple antenna elements which together can be used to synthesize antenna patterns with narrower beams and lower sidelobes as compared to single-element antennas. More specifically, many applications which require high directivity, narrow beam patterns with low sidelobes include: (1) radars, which often use a narrow beam to detect targets for achieving a better angular resolution, higher signal-to-noise ratio (SNR), and low sidelobes to avoid ambiguity coming from signal returns from other directions; (2) modern cellular phone base stations which employ specially shaped beam patterns to provide uniform signal strength with the coverage area while minimizing radiation into the sky; (3) newest satellite communications/broadcasting systems which adopt spotlight beams to cover specific zones while reducing interference into neighboring areas for enhanced security and SNR. The first array antennas for producing shaped directive beam patterns were introduced during World War II for early radar systems using an array of dipole elements. The disadvantages of such a dipole array were that the dipole elements were large 3D objects requiring manual labor to produce and the design was difficult to use for higher frequency such as for X band or higher. (open full item for complete abstract)

Committee: Chi-Chih Chen (Advisor); Gabriel Conant (Committee Member); Robert Lee (Committee Member); Emre Ertin (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Electromagnetism; Engineering

Master of Science, The Ohio State University, 2007, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 2006, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 2007, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 2005, Graduate School

Committee: Not Provided (Other) Subjects:

Doctor of Philosophy, The Ohio State University, 2023, Electrical and Computer Engineering

Array signal processing algorithms for direction finding and adaptive beamforming require accurate in-situ calibration of the antenna array. Unfortunately, calibrating the array inside an anechoic chamber is often not possible because the array, or the platform it is mounted on, is too large. In addition, simulations of the array using Computational Electromagnetic (CEM) software can miss crucial information about the manufacturing defects present in the real system. The limitations of these methods has lead to the development of in-situ calibration techniques that can exploit the signals the array receives while deployed in its operational environment (i.e. Signals of Opportunity [SoOp]). In-situ calibration is advantageous because the incident signals include the effects of platform scattering and manufacturing defects without the need for an anechoic chamber. However, without any coordination between the array and the sources generating the SoOp, the transmitted signals are unknown to the array and multiple SoOp can be received simultaneously. Current methods capable of using SoOp for calibration rely on restrictive models for the array response, such as the Mutual Coupling Matrix, and are unable model the effects of platform scattering. In this dissertation, we present an in-situ calibration technique that incorporates a flexible model for the array response based on a Spherical Mode Expansion (SME). By expressing the far-field patterns of the antenna elements as a SME, we are able to model the response of an array placed in a complex scattering environment using a relatively compact representation. Because the spherical harmonics are only orthogonal over the full sphere, computing the expansion coefficients is difficult when the measurement region is limited, which is a common occurrence in in-situ calibration. We resolve this issue by employing a regularized least-squares solution and an efficient regularization parameter selection procedure. The propose (open full item for complete abstract)

Committee: Inder Gupta (Advisor); Patricia Enciso (Committee Member); Fernando Teixeira (Committee Member); Joel Johnson (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Master of Science in Engineering, University of Akron, 2018, Electrical Engineering

This thesis discusses a detailed study of the design and performance analysis of patch antenna arrays at different frequencies. A linear hybrid array of 16 elements is built using patch antennas integrated with an RF front-end using commercial off-the-shelf (COTS) components. A well organized receiver chain that can work at a frequency in the range of 5 - 6 GHz is built using chip level components on a printed circuit board (PCB). This study mainly emphasizes the design and implementation of the comprehensive receiver beamforming systems using fast Fourier transform (FFT) algorithm and approximate - discrete Fourier transform (a-DFT). A low complexity 32-beam multi-beamformer at 5.8 GHz is designed, built and implemented in real time using optimized digital FPGA cores as the digital back-end which is collaborated work with Viduneth Ariyarathna. The emanating beams were measured and verified using the FPGA - based 32-element 5.8 GHz array setup which can generate 120 MHz bandwidth per channel. The beams corresponding to the approximate DFT are in good agreement with the beams corresponding to the FFT with negligible error approximately less than -14 dB. This setup can be used as a test bed to measure and evaluate various signal processing algorithms up to 32 linear array elements.

Committee: Arjuna Madanayake Dr (Advisor); Nghi Tran Dr (Committee Member); Ryan Christopher Toonen Dr (Committee Member) Subjects: Computer Engineering; Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2018, Electrical and Computer Engineering

Wireless communication networks have become ubiquitous in recent years. Current wireless applications are possible thanks to small WiFi cells that provide high-speed indoor coverage and outdoor macro-cells that support user mobility. Next generation wireless networks will use similar architectures to enable new applications such as augmented and virtual reality, the internet of things, ultra-high definition video streaming, and massive data transmission and storage. However, these applications require unprecedented high-speed data transfer capabilities enabled by large frequency bandwidths. Motivated by spectrum scarcity in bands below 6 GHz, previously unused millimeter-wave (mmWave) bands, where large bandwidths are available, are now considered for future wireless networks. The necessity for efficient communication techniques for such large bandwidths and mmWave frequencies is the main motivation for this dissertation, with a focus on the complex radiowave propagation conditions found in indoor environments. Propagation mechanisms such as multiple reflections, diffractions, and transmissions through walls are commonly found in indoor wireless communications, which cause variations in the received signal along its bandwidth (wideband or frequency-selective channels). Traditionally, antenna arrays have been used together with beamforming (linear processing) techniques to improve the system's performance. However, those techniques were designed for narrowband systems (e.g., zero-forcing or matched filtering) and their application to wideband systems requires additional processing that increases system's complexity. In the first part of this dissertation, we tackle the problem of beamforming in frequency-selective channels with two approaches: \emph{i}) we use the electromagnetic time-reversal (TR) effect to directly design novel wideband beamformers, and \emph{ii}) we generalize the block-diagonalization (BD) procedure used in narrowband channels to the freque (open full item for complete abstract)

Committee: Fernando Teixeira (Advisor) Subjects: Electrical Engineering

Master of Science, University of Akron, 2017, Electrical Engineering

Radio frequency (RF) antenna array beamforming based on electronically steerable wideband phased-array apertures find applications in communications, radar, imaging and radio astronomy. High-bandwidth requirements for wideband RF applications necessitate hundreds of MHz or GHz frame-rates for the digital array processor. Systolic array architectures are often employed in multi-dimensional (MD) signal processing for linear and rectangular antenna arrays. Thus, this research used a FPGA hardware platform, the ROACH-2, which is equipped with a Xilinx Virtex-6 SX475T FPGA chip, and which is widely used in the field of radio astronomy. The research concentrated on the prospects of implementation of systolic array based MD beamformers on the ROACH-2, and on methods of extending the operating frequency to GHz range by using polyphase structures. The proposed systolic array architectures employ a differential form 2-D IIR frequency planar beam filter structure which is low in hardware utilization. The study highlights techniques that can be used to overcome the limitations of the ROACH-2 signal processing platform to achieve high operating frequencies.

Committee: Arjuna Madanayake (Advisor); Subramaniya Hariharan (Committee Member); Joan Carletta (Committee Member) Subjects: Communication; Electrical Engineering; Engineering

Doctor of Philosophy, The Ohio State University, 1986, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1985, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1984, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1983, Graduate School

Committee: Not Provided (Other) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 1983, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1983, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1983, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1983, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1983, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1983, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1982, Graduate School

Committee: Not Provided (Other) Subjects: Engineering