Doctor of Philosophy, The Ohio State University, 2011, Electrical and Computer Engineering

There is strong interest to combine many antenna functionalities within a single, wideband aperture. However, size restrictions and conformal installation requirements are major obstacles to this goal (in terms of gain and bandwidth). Of particular importance is bandwidth; which, as is well known, decreases when the antenna is placed closer to the ground plane. Hence, recent efforts on EBG and AMC ground planes were aimed at mitigating this deterioration for low-profile antennas. In this dissertation, we propose a new class of tightly coupled arrays (TCAs) which exhibit substantially broader bandwidth than a single patch antenna of the same size. The enhancement is due to the cancellation of the ground plane inductance by the capacitance of the TCA aperture. This concept of reactive impedance cancellation was motivated by the ultrawideband (UWB) current sheet array (CSA) introduced by Munk in 2003. We demonstrate that as broad as 7:1 UWB operation can be achieved for an aperture as thin as λ/17 at the lowest frequency. This is a 40% larger wideband performance and 35% thinner profile as compared to the CSA. Much of the dissertation's focus is on adapting the conformal TCA concept to small and very low-profile finite arrays. Three particular designs are presented. One is a 6x6 patch array occupying a λ/3 x λ/3 small aperture (mid-frequency is at 2.1 GHz). Remarkably, it is only λ/42 thick yet delivers 5.6% impedance bandwidth (|S11| < -10dB), 4.4dB realized gain (87% efficiency) and 23% gain bandwidth (3dB drop). The second finite TCA consists of 4x2 patches and occupies a λ/3.2 x λ/3.2 aperture on a λ/26 thick substrate (mid-frequency is at 2 GHz). This antenna delivers 17.3% impedance bandwidth, 4.8dB realized gain (95% efficiency) and 30% gain bandwidth. That is, more than twofold impedance bandwidth is delivered as compared to a single patch antenna of the same size on conventional or EBG substrate. The third array being considered consists of 3x2 patches occu (open full item for complete abstract)

Committee: John L. Volakis PhD (Advisor); Kubilay Sertel PhD (Advisor); Robert J. Burkholder PhD (Committee Member); Fernando L. Teixeira PhD (Committee Member) Subjects: Electrical Engineering; Electromagnetics

MS, University of Cincinnati, 2006, Engineering : Electrical Engineering

With the drive towards better and faster communication systems, wireless communications has assumed a new significance in today's world. Further, with the rapid miniaturization and incorporation of RF technology in IC's, the real estate area available for a circuit has been greatly reduced. A good example of this integration of RF, analog and digital circuits on a single chip would be the three dimensional monolithic integrated circuits developed at the University of Cincinnati. In this context, it becomes all the more important to increase the efficiency of the antennae involved with these systems. This thesis tries to do just that by determining an optimum design for a patch antenna and also the best possible feed network for the same which would enhance its radiation properties as has been shown through the results obtained here. Patch antennae are used because of their popularity arising from their adaptability and unobtrusive nature. Furthermore, the mutual coupling between antennae in a 2 x 2 array when the antennae are linearly, non-linearly and circularly polarized is studied and compared. During this process, the frequency variation produced in such a situation was also tabulated. The data from the variation of the mutual coupling between adjacent antennae and the resonant frequency of the antennae themselves, its dependence on polarization, feed direction and distance can be used in designing an array.

Committee: Dr. Altan Ferendeci (Advisor) Subjects:

Master of Science in Electrical Engineering (MSEE), Wright State University, 2019, Electrical Engineering

This study focuses on the use of microstrip antenna technology for designing an ultra-wideband antenna to meet low size, weight and power requirements. Based on the recent literature for such antennas, a quasi-log periodic microstrip antenna array is designed to operate from 8 to 40 GHz (radar bands X, Ku, K and Ka). The array consists of 33 co-linear, inset-fed, square patches on a Roger's Duroid substrate, and is modeled using the Advanced Design System software from Keysight. The simulated results show the antenna has pass-band gains greater than 5 dB, a half-power beamwidth of 30 degrees, and linear polarization with a broadside radiation pattern. In addition, the fractional voltage standing wave ratio is less than 1.8 for 18 GHz of the pass-band, and the antenna has an efficiency greater than 60 percent over the entire pass band.

Committee: Michael A. Saville Ph.D., P.E. (Advisor); Yan Zhuang Ph.D. (Committee Member); Saiyu Ren Ph.D. (Committee Member); Josh Ash Ph.D. (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Technology

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

Doctor of Philosophy (PhD), Wright State University, 2020, Engineering PhD

Different additive manufacturing (AM) methods including fused deposition modeling (FDM) and piezoelectrical drop on demand (DOD) inkjet printing have been used in printed electronics for easy production, easy integration, better performance, and low cost. These methods have been used in producing everyday smart printed electronics such as conformal antennas (planner and non-planar antennas), sensors, actuators, and solar cells created on flexible and rigid substrates. The performance of printed electronics strongly depends on printing techniques and printing resolution that enhance their electrical and mechanical properties. In this dissertation, 3D and surface printing techniques were used to enhance the performance of printed electronics devices fabricated on rigid and flexible substrates. First, fused deposition modeling (FDM) technique was used to study the effect of 3D printed heterogeneous substrates on radio frequency response of microstrip patch antennas. Microstrip patch antennas created on acrylonitrile butadiene styrene (ABS) substrates that were designed by 3D CAD design software (SOLIDWORKS) with dimension 50mm x 50mm x 5mm and fabricated with different machine infill densities 25%, 50%, and 75% using FDM 3D printer. Then, 3D X-ray microscope was used to measure the actual volume fraction and construct equivalent simulations for series and parallel equivalent dielectrics constant. The patch antennas were tested for resonant frequency using a vector network analyzer (VNA) combined with ANSYS-HFSS simulation that was developed based on the permittivity anisotropy in 3D printed heterogeneous substrates to estimate the bulk permittivity of ABS material and study the effect of varying the dielectric constant in lateral and thickness direction. Also, microstrip patch antenna with dimension 30mm x 25mm, was modeled on polydimethylsiloxane (PDMS) substrate with the same dimension of ABS substrate and analyzed for resonant frequency using A (open full item for complete abstract)

Committee: Ahsan Mian Ph.D. (Advisor); Raghu Srinivasan Ph.D. (Committee Member); Hong Huang Ph.D. (Committee Member); Henry D. Young Ph.D. (Committee Member); Amir Alfalahi Ph.D. (Committee Member) Subjects: Mechanical Engineering

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

Master of Science in Mechanical Engineering (MSME), Wright State University, 2017, Mechanical Engineering

Three-dimensional (3D) printing, a form of Additive manufacturing (AM), is currently being explored to design materials or structures with required Electro-Mechanical-Physical properties. Microstrip patch antennas with a tunable radio-frequency (RF) response are a great candidate for 3D printing process. Due to the nature of extrusion based layered fabrication; the processed parts are of three-layer construction having inherent heterogeneity that affects structural and functional response. The purpose of this study is to identify the relationship between the anisotropy in dielectric properties of AM fabricated acrylonitrile butadiene styrene (ABS) substrates in the RF domain and resonant frequencies of associated patch antennas and also to identify the response of the antenna before and after a low velocity impact. In this study, ANSYS high frequency structure simulator (HFSS) is utilized to analyze RF response of patch antenna and compared with the experimental work. First, a model with dimensions of 50 mm x 50 mm x 5 mm is designed in Solidworks and three separate sets of samples are fabricated at three different machine preset fill densities using an extrusion based 3D printer LulzBot TAZ 5. The actual solid volume fraction of each set of samples is measured using a 3D X-ray computed tomography microscope. The printed materials appeared to exhibit anisotropy such that the thickness direction dielectric properties are different from the planar properties. The experimental resonant frequency for one fill-density is combined with ANSYS-HFSS simulation results to estimate the bulk dielectric constant of ABS and the equivalent dielectric properties in planar and thickness directions. The bulk dielectric properties are then used in HFSS models for other two fill densities and the simulated results appear to match reasonably well with experimental findings. The similar HFSS modeling scheme was adopted to understand the effect of material heterogeneity on RF response. In (open full item for complete abstract)

Committee: Ahsan Mian Ph.D. (Advisor); Raghavan Srinivasan Ph.D. (Committee Member); Joy Gockel Ph.D. (Committee Member) Subjects: Aerospace Engineering; Automotive Engineering; Design; Electrical Engineering; Mechanical Engineering; Mechanics; Plastics; Technology