Theses/Dissertations - Electrical and Computer Engineering
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Browsing Theses/Dissertations - Electrical and Computer Engineering by Author "Baylis, Charles Passant, 1979-"
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Item Adaptive load impedance optimization for power amplifiers in reconfigurable radar transmitters.(2013-05-15) Martin, Joshua Lee.; Baylis, Charles Passant, 1979-; Electrical and Computer Engineering.; U.S. Naval Research Laboratory.; Baylor University. Dept. of Electrical and Computer Engineering.A fundamental tradeoff exists in radar transmitter design between linearity and efficiency due to the signal amplification. These transmitters are driven into saturation in order to increase efficiency, but may potentially violate regulatory spectral mask limitations. An adaptive method for optimizing linearity and efficiency for power amplifiers in radar transmitters is presented. This approach uses intelligent search techniques with load-pull measurements for power-added efficiency (PAE) and adjacent channel power ratio (ACPR) to dynamically maximize the PAE while meeting spectral requirements. Using load-tuning, an algorithm performs a steepest ascent search for the PAE optimum load reflection coefficient, followed by a steepest descent search for ACPR. The steepest descent search, when begun at the PAE optimum, approximates the Pareto optimal frontier between the two objectives. This trace enables PAE to be maximized for an imposed limit on ACPR, optimizing the performance of adaptive radar transmitters under spectral mask constraints.Item Algorithms for fast power amplifier load impedance and input power optimization using the Power Smith Tube.(2016-04-08) Barkate, Joseph G., 1991-; Baylis, Charles Passant, 1979-The increasing number of devices occupying the finite wireless broadband spectrum has led to serious concerns regarding spectral congestion. To facilitate radar and communication spectral coexistence, reconfigurable, adaptive amplifiers are expected to be a critical component in future cognitive radar transmitters. This work details a method to visualize and simultaneously optimize the load reflection coefficient and input power of a power amplifier device in order to achieve the highest possible efficiency while meeting a predefined spectral spreading constraint. The proposed vector-based search utilizes gradients as well as momentum in the Power Smith Tube in order to optimize accurately with as few experimental queries as possible. This method is proven to be feasible in higher dimensions, allowing for future implementation in real-time reconfigurable power amplifiers.Item Circuit modeling and optimization techniques for next-generation radar.(2018-04-24) Hays, Zachary Samuel, 1994-; Baylis, Charles Passant, 1979-Spectral emission requirements for radar systems are becoming increasingly strict. Future radar systems will require well-designed, reconfigurable circuitry to coexist with the myriads of wireless devices using the spectrum. There are two main goals of this research. The first goal is to demonstrate circuit optimization algorithms implemented in real-time with two types of fast tuners. The optimization algorithms can tune the fundamental tuning elements of the tuner to quickly find an efficient operating point for the power amplifier while staying within spectral constraints. Secondly, this thesis presents a new method to model wideband low-noise amplifiers for use in receiver circuits using the Volterra Series. Both of these contributions are expected to enhance design and implementation of future radar systems.Item Circuit optimization and frequency agility for cognitive radar.(2018-04-27) Rezayat, Sarvin, 1994-; Baylis, Charles Passant, 1979-Due to the increased demand on the spectrum, radars are in increased stress to participate in dynamic spectrum allocation. Therefore, the next generation radar will be an adaptable cognitive radar. This type of radar will be require reconfigurable circuitry. This paper explores real-time circuit optimization for a cognitive radar test bench. This will include the use of two type of reconfigurable matching networks. The first one is a varactor matching network that is very quick but experiences non-linearity. The other is an evanescent-mode resonant cavity tuner that handles high input power but experiences stability and relatability issues. This thesis tackles strategies to mitigate the non-ideal behavior of these networks. The implementation of frequency agility with circuit optimization is also demonstrated.Item Design, simulation, construction, and measurement testing of fast-reconfigurable radio frequency switched-stub matching networks.(2021-04-21) Calabrese, Caleb Benjamin, 1996-; Baylis, Charles Passant, 1979-Today’s world is increasingly dependent on wireless communications, and fifth generation (5G) cellular technologies have recently entered the picture. Part of their designated spectrum overlaps with that of S-band radar systems. In order to effectively share the spectrum, the high-power radar systems must be able to transition to alternate operating frequencies in real time. To do this without sacrificing transmit range requires reconfigurable matching networks placed in between the power amplifiers and phased-array antenna elements in the radar transmitters which must be able to meet the power and speed requirements of the system. Historically, tuners have struggled to meet both requirements simultaneously. This thesis presents a simulated design, an algorithm to optimize reconfigure the circuit as operating conditions change, a low-power prototype switched-stub reconfigurable matching network, and a prototype taking advantage of custom semiconductor plasma technology with the purpose of progressing towards a solution that meets the radar system requirements.Item Enabling and directing real-time cognitive radar transmitter optimization.(2021-10-27) Egbert, Austin S., 1995-; Baylis, Charles Passant, 1979-As the available wireless spectrum grows more crowded with increased usage from high bandwidth telecommunications applications, it becomes infeasible for many other users of wireless spectrum to continue operating with static, inflexible methods. Among these users are radar systems, which have historically been allocated large sections of bandwidth. In order to adapt and coexist with new technology in a dynamically managed environment, next generation radars must be able to adjust their spectral configuration in real time. The research presented in this dissertation provides a framework that can be used for determining transmission constraints over both spatial direction and signal frequency. While existing research has demonstrated how to optimize radar transmitters using adjustable amplifier matching networks, such optimizations have not been able to complete quickly enough for use in real-time adaptation. To accelerate these optimizations, this dissertation presents a faster method for evaluating the performance of transmit amplifiers using a software-defined radio (SDR) and a load-pull extrapolation method using deep learning image completion techniques. Additionally, the accelerated optimization technique has been adapted for use with the pulse-to-pulse waveform agility paradigm of cognitive radars. Finally, the impact on Doppler detection accuracy of modifying the radar transmit chain during a coherent radar processing interval is analyzed, along with techniques for correcting the resulting distortions.Item Faster circuit optimization techniques for full-band and notched waveforms to enable next-generation radar.(2020-04-14) Dockendorf, Angelique Anne, 1997-; Baylis, Charles Passant, 1979-As the wireless spectrum becomes increasingly congested, more efficient sharing of the spectrum is desperately needed. In order to coexist, next-generation radars will have to adapt their spectral use in real-time. Two useful baseline technologies in interference-avoiding, adaptive spectrum technologies are the fast reconfiguration of the transmitter power amplifier circuitry and the transmission of spectrally notched waveforms. This thesis presents two algorithms for the real-time circuit optimization necessary in spectrally agile radars: a modified gradient search algorithm for application to a high-power, evanescent-mode cavity tuner that uses previous results to improve reconfiguration time and a modified gradient search algorithm compatible with spectrally notched waveforms. Additionally, this work discusses iterative circuit optimization algorithms for a designed electrically actuated switched-stub tuner.Item Joint circuit and waveform optimization for next-generation radar.(2018-04-17) Latham, Casey, 1993-; Baylis, Charles Passant, 1979-Due to congested wireless radio spectrum, next-generation radar transmitters will need to be adaptive and reconfigurable in real time to share spectrum with wireless communication devices. Typical system optimization methods rely on separate optimization of the circuit and waveform, which can lead to an over-emphasis on one criteria. While the end result may be acceptable, the intermediate results may not be desirable for a real-time situation. In this thesis, a joint circuit and waveform optimization technique is demonstrated that is designed for use in a real-time reconfigurable radar transmitter. Measurement results are presented to show how joint circuit and waveform optimization allows for better intermediate results that allow real-time optimization to be utilized.Item Multidimensional power amplifier circuit optimizations for adaptive radar.(2017-03-30) Fellows, Matthew, 1989-; Baylis, Charles Passant, 1979-As wireless technology and dynamic spectrum allocation continue to proliferate, the ability to dynamically reconfigure radar transmitter power amplifiers will become necessary for adaptive radar. Reconfigurable transmitters will require the ability to tune input parameters such as load impedance, waveform bandwidth, and amplifier bias voltage to provide excellent performance while adjusting to real-time changes in requirements. This dissertation presents design tools and search algorithms to maximize power-added efficiency (PAE) while providing compliance with spectral regulations and transmitting sufficient power. The presented contributions include 1) the S metric for spectral compliance, 2) the Smith Tube as a tool for design and optimization, 3) optimization algorithms to maximize waveform bandwidth using the Bandwidth Smith Tube, 4) an optimization for power-added efficiency under adjacent-channel power ratio (ACPR) constraints in the Bias Smith Tube, and 5) an optimization for power-added efficiency, adjacent-channel power ratio, and output power demonstrated on the Smith Chart and in the Bias Smith Tube. These algorithms will be applicable toreal-time reconfiguration for adaptive radar systems.Item Phased array impedance tuning, secure transmission, and nonlinear spatial intermodulation suppression for next-generation radar and communications systems.(2020-03-30) Rodriguez-Garcia, Pedro Alejandro, 1992-; Baylis, Charles Passant, 1979-Simultaneously transmitting radar and communications signals from the same multi-beam phased array system, using spatial diversity, allows multiple functions to use the same frequency and can alleviate spectral congestion. An issue arises, however in a transmitter array that consists of power amplifiers connected to the antenna elements. Undesired spatial intermodulation beams are transmitted as a result of the nonlinearities in these power amplifiers and can degrade both radar and communications mission abilities. The research presented in this dissertation resolves the nonlinear intermodulation products caused by these power amplifier nonlinearities by element-wise impedance tuning between each power amplifier and antenna element to reverse the nonlinear distortion effects. To emphasize the importance of the flexibility that elementwise impedance tuning provides, the analysis of a single-beam phased array transmitter is presented to demonstrate the dynamic improvement in range for both radar and communications scenarios individually. The improvement results from resolving the mismatch between the antenna elements due to mutual coupling as the array scan angle changes. Finally, to ensure secure communications messages while maintaining radar capabilities, a directional modulation technique is presented, as well as Barker code sequencing, to maintain communications security in the transmit and receive mode of the radar.Item Power-amplifier optimization using tunable circuitry and stability analysis methods for the next generation radar.(2018-04-17) Hays, Lucilia R., 1993-; Baylis, Charles Passant, 1979-In response to the increasingly congested and contested wireless spectrum, the next generation radar must be adaptive and reconfigurable. A reconfigurable power amplifier is a necessary component of the cognitive radar system. The reconfigurable power-amplifier must operate efficiently and stably while maintaining spectrum compliance. The research in this thesis presents state-of-the-art tuning algorithms for optimizing the load reflection coefficient presented to a transistor by novel tunable circuitry. The algorithms are implemented on systems using a varactor diode network and a high-power handling evanescent mode cavity tuner as the tunable load matching networks. In addition, stability considerations are explored. A new amplifier design tool, the frequency Smith Tube, is presented which allows for broadband stability analysis for small-signal inputs. A real-time stability analysis procedure based on the acceleration of transducer gain during optimization is also presented.Item Side lobe modulation of radar antenna pattern utilizing an auxiliary array.(2013-05-15) Wang, Loria LayShay.; Baylis, Charles Passant, 1979-; Electrical and Computer Engineering.; Baylor University. Dept. of Electrical and Computer Engineering.In the area of electronic countermeasures, disabling the ability of an individual to “listen” to the transmitted waveform is of great interest. Most often, an individual can intercept the transmitted radar signal through the side lobes of the transmitted radiation pattern. Reducing these transmitter side lobes may eliminate the ability of unauthorized listeners to intercept a transmitted signal. Most traditional radar systems utilize antennas that do not possess the capability of shaping the transmitted radiation pattern. Instead of replacing the existing radar antenna with large adaptive arrays, the combination of the existing system with an auxiliary low cost array will extend the system capability to include techniques such as side lobe modulation, cancellation, and adaptive beam forming.