Thesis (Ph. D.)--Michigan State University. Dept. of Electrical and Computer Engineering, 2006. / Title from PDF t.p. (viewed on Nov. 17, 2008) Includes bibliographical references (p. 155-160). Also issued in print.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2006. / Dr. Jonathan Colton, Committee Chair ; Dr. John Muzzy, Committee Member ; Dr. Daniel Baldwin, Committee Member ; Dr. John Schultz, Committee Member.

Since its invention, phased array has been extensively applied in both military and civil areas. The applications include target detecting and tracking, space probe communication, broadcasting, human-machine interfaces, and remote sensing. Although the phased array applications show a broad range of potential market, there are some limitations of phased array's development: high cost, complex structure, narrow bandwidth, and high power consumption. Therefore, novel ideas are needed to reduce these constraints. In this thesis, several new approaches about the design and application of phased array are presents. First, the principle of phased array and fundamental design equations are introduced. Second, a new application of phased array antenna for radar respiration measurement is presented. By integrating a 4×4 Butler matrix with four-element antenna array, there will be four distinct main beams in radiation pattern. This new approach can improve the measurement accuracy and realize a high detecting rate. Third, a compact phased array antenna system based on dual-band operations is introduced. Dual-band function can make N-antenna system obtain 2N unique radiation beams (N is an integer) and achieve a significant size reduction compared to the conventional single-band system. To verify the design concept, a four-element phased array antenna working at 5GHz and 8GHz is designed and fabricated. The measurement results make a good agreement with the simulations. Finally, a novel architecture of steering phase feeding network by using bi-directional series-fed topology is presented. This bi-directional series-fed network needs less phase shifters and realizes steering phase function by applying control voltage.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 216-221).

The use of parallel imaging techniques for image acceleration is now common in clinical magnetic resonance imaging (MRI). There has been limited work, however, in translating the parallel imaging techniques to routine animal imaging. This dissertation describes foundational level work to enable parallel imaging of mice on a 4.7 Tesla/40 cm bore research scanner. Reducing the size of the hardware setup associated with typical parallel imaging was an integral part of achieving the work, as animal scanners are typically small-bore systems. To that end, an array element design is described that inherently decouples from a homogenous transmit field, potentially allowing for elimination of typically necessary active detuning switches. The unbalanced feed of this "dual-plane pair" element also eliminates the need for baluns in this case. The use of the element design in a 10-channel adjustable array coil for mouse imaging is presented, styled as a human cardiac top-bottom half-rack design. The design and construction of the homogenous transmit birdcage coil used is also described, one of the necessary components to eliminating the active detuning networks on the array elements. In addition, the design of a compact, modular multi-channel isolation preamplifier board is described, removing the preamplifiers from the elements and saving space in the bore. Several additions/improvements to existing laboratory infrastructure needed for parallel imaging of live mice are also described, including readying an animal preparation area and developing the ability to maintain isoflurane anesthesia delivery during scanning. In addition, the ability to trigger the MRI scanner to the ECG and respiratory signals from the mouse in order to achieve images free from physiological motion artifacts is described. The imaging results from the compact 10-channel mouse array coils are presented, and the challenges associated with the work are described, including difficulty achieving sample-loss dominance and signal-to-noise ratio (SNR) limitations. In conclusion, in vivo imaging of mice with cardiac and respiratory gating has been demonstrated. Compact array coils tailored for mice have been studied and potential future work and design improvements for our lab in this area are discussed.

Cognitive radio networks require the use of computational resources to reconfigure transmit/receive parameters to improve communication quality of service or efficiency. Recent emergence of smart phones has made these resources more accessible and mobile, combining sensors, geolocation, memory and processing power into a single device. Thus, this work examines an integration of a smart phone into a complex radio network that controls the beam direction of a phased array using a conventional method, but utilizes the phone's internal sensors as an enhancement to generate beam direction information, Bluetooth channel to relay information to control circuitry, and Global Position System (GPS) to track an object in motion. The research and experiments clearly demonstrate smart phone's ability to utilize internal sensors to generate information used to control beam direction from a phased array. Computational algorithms in a network of microcontrollers map this information into a DC bias voltage which is applied to individual phase shifters connected to individual array elements. To test algorithms and control theory, a 4 by 4 microstrip patch array is designed and fabricated to operate at a frequency of 2.4 GHz. Simulations and tests of the array provide successful antenna design results with satisfactory design parameters. Smart phone control circuitry is designed and tested with the array. Anechoic test results yield successful beam steering capability scanning 90 degrees at 15 degree intervals with 98% accuracy in all cases. In addition, the system achieves successful beam steering operable over a bandwidth of 100 MHz around resonance. Furthermore, these results demonstarate the capability of the smart phone controlled system to be used in testing further array formations to achieve beam steering in 3-Dimensional space. It is further noted that the system extends capabilities of integrating other control methods which use the smart phone to process information.

Modern satellite, wireless communications, and radar systems often demand wideband performance for multi-channel and multi-function operations. Among these applications, phased array antennas play an important role. This dissertation covers two wideband phased array antennas, one produces linear polarization and one produces circular polarization. The main difference between these two phased array antennas is the antenna array. For the linearly polarized array, a wideband microstrip line to slotline transition is used to feed a Vivaldi antenna. For the circularly polarized array, a wideband microstrip line to parallel stripline transition is used to feed a spiral antenna. From 3 to 12 GHz, the linearly polarized beam is steered over ± 15º. Since the electromagnetic spectrum is limited and has to be shared, interference is getting serious as more and more wireless applications emerge. Filters are key components to prevent harmonic interference. The harmonic signals can be suppressed by cascading additional lowpass filters or bandstop filters. A bandstop filter combining shunt open stubs and a spurline is proposed for a compact size and a deeper rejection. Two lowpass filters with interdigital capacitors and slotted ground structures are also studied. Harmonic suppression can also be achieved with the modification of bandpass filters. Three conventional bandpass filters with spurious passbands are investigated. The first one is a dual-mode patch bandpass filter. The second passband of the proposed filter is at 2.88fo, where fo is the fundametal frequency. The second filter is an open-loop bandpass filter. Two open stubs are added to achieve high suppression in the second harmonic signal. The suppression of 35 dB at the second harmonic is obtained. For the third filter using half-wavelength open stubs, a T-shaped line is used to replace the quarter-wavelength connecting line. The T-shaped line has the same response with the connecting line in the passband. Furthermore, the T-shaped line works as a bandstop filter at the second harmonic. Finally, a new compact slow-wave resonator and bandpass filters are presented. A simple transmission-line model is used to predict the resonant frequency. Compared with the conventional uniform half-wavelength resonator, the slow-wave resonator shows a 25% size reduction.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 164-178). Available also in a digital version from Dissertation Abstracts.

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

Thesis (M.S. in Engineering Science (Electrical Engineering)--Naval Postgraduate School, December 2003. / Thesis advisor(s): David C. Jenn, Roberto Cristi. Includes bibliographical references (p. 75-76). Also available online.