Viability of Ka-Band Solid-State Power Amplifiers For High-Rate Data Transmission In Space Communications A thesis presented to the Graduate School of the University of Cincinnati in partial fulfillment of the requirements for the degree Master of Science in the School of Electrical Engineering and Computer Science of the College of Engineering and Applied Science Christopher A. Drummond B.S. Ohio University October 2019 Committee Chair: Dr. Altan Ferendeci Abstract The United States launches over 20 space vehicles every year. Each vehicle has an important mission to which large amounts of money have been allocated in order to support the growth of the ever-changing country and world as we move into the future. Earth science data gathered by satellites is transmitted down to Earth, and probes and rovers are sent out into our solar system to gather data about our solar system which must be transmitted back as well since these vehicles are generally expected to remain out in space forever. Sensors and other data- gathering devices are more capable now than ever of generating huge amounts of data, and it must be transmitted back to Earth at high rates with few errors. The primary focus of the research performed here was to investigate the viability of Ka- band solid-state power amplifiers for use in future space programs as replacements for travelling- wave-tube amplifiers, as well as determining optimal design techniques to fit current flight-ready technology. The research was performed as part of an Internal Research and Development (IRAD) project for L3 Technologies Cincinnati Electronics (L3 CE hereafter), which is a world- leading space communications developer. Many gain lineups were designed and simulated so that the best one could be built into a prototype. Simulations for the circuitry and microwave structures were performed in AWR Microwave Office and the best design was built and tested. The amplifier prototype was built to maximize the power efficiency and transmit bandwidth so that high-rate modulated data could be transmitted without error and without consuming too much power or generating too much excessive heat to be managed by satellite systems. A battery of typical flight-readiness tests was performed on the prototype. Afterwards, analysis of the data gathered was performed in order to illuminate the discrepancies between the simulated data and the measured data. The research demonstrated that Ka-band solid-state power amplifiers are indeed viable replacements for travelling-wave-tube amplifiers for high-rate data transmission. The power amplifier produced more than 10 watts across the bandwidth of interest. The transmit bandwidth of the prototype exceeded 1.5 GHz at a power-added efficiency (PAE) of 27.1% which is enormously beneficial for the efficient transmission of huge amounts of data. With that bandwidth and efficiency (and improvements on them in the future), flight-ready hardware will be capable of transmitting data at rates far exceeding 1 Gbps. There is now a viable argument to be made by space communication companies about the benefits of using solid-state power amplifiers over travelling-wave-tube amplifier for very high data rate transmission. Acknowledgements I am very thankful for all the people around me who were willing to support my efforts in this research. I thank my parents for creating the opportunity for me to pursue advanced education and the University of Cincinnati for fostering an environment for me to succeed. I would like to thank Dr. Chris G. Bartone, my undergraduate advisor from Ohio University. Without his guidance, I probably never would have pursued graduate studies in RF and never would have seen the benefits of knowledge, skill, and perseverance fostered by advanced education. Without him recognizing my talents and sponsoring me in my efforts, I never would have made it to where I am today. I would also like to thank Dr. Marc Cahay, the department chair of the school of Electrical Engineering and Computer Science at the University of Cincinnati College of Engineering and Applied Science. His gracious allowance for me to continue my graduate studies after the roughest times of my life nearly caused me to quit was a blessing and without it I would never have overcome the adversity presented to me in life to achieve the degree Master of Science. I would like to thank many people at Cincinnati Electronics as well. Firstly, I thank Dr. Bob Hayes, the fromer Director of Advanced Programs in charge of the IRAD project from which this thesis grew. Without his support, I likely would have forgone graduate study and research and never would have had the opportunity to contribute to space programs in this way. I would also like to thank Jim Lundt, my direct manager. His experience in the design, simulation, build, and implementation of RF systems made him a perfect mentor for me. Without his advice, my design may have never succeeded and I may never have finished this degree. I’d also like to thank the entire senior management team at L3 for making it possible to continue education after beginning full-time work and allowing the use of in-house equipment which allowed the full testing of this project to be performed at frequencies beyond the capabilities of the equipment at the University of Cincinnati. Cincinnati Electronics encourages all employees to reach for the stars in education, knowledge, and skill, and I can’t thank them enough for creating an environment which sets up so many to succeed. Table of Contents Abstract .......................................................................................................................................... 2 Acknowledgements ....................................................................................................................... 5 Table of Contents .......................................................................................................................... 7 Table of Figures ............................................................................................................................ 8 Chapter 1: Introduction ............................................................................................................. 11 Background .......................................................................................................................... 11 High-Frequency Data Links ............................................................................................... 12 Replacing Travelling Wave Tube Amplifiers .................................................................... 14 Methodology ......................................................................................................................... 17 Chapter 2: Space-Qualifiable Ka-band Components .............................................................. 20 Component Spaceflight Capability .................................................................................... 20 Space Environmental Effects .............................................................................................. 21 Radiation Sources and Effects in Space............................................................................. 23 Radiation Effects on Electronic Components and Mitigation Techniques .................... 24 Support Component Selection ............................................................................................ 26 Amplifier Devices ................................................................................................................. 28 Chapter 3: Analytical Design ..................................................................................................... 30 Concept of Operation .......................................................................................................... 30 Basic Power Amplifier Design and Background............................................................... 35 Transmission Lines .............................................................................................................. 37 Ring Coupler Design and Analysis ..................................................................................... 43 Final Amplifier Design ........................................................................................................ 47 Driver Amplifier Design ...................................................................................................... 49 Amplifier Stability ............................................................................................................... 51 Chapter 4: Software-Based Simulation and Data .................................................................... 55 Scope ..................................................................................................................................... 55 Driver Amplifier Subassembly Simulation ....................................................................... 56 Final Amplifier Subassembly Simulation .......................................................................... 64 Top-Level Amplifier Simulation ........................................................................................ 71 Chapter 5: Prototype Testing and Data .................................................................................... 74 Driver Amplifier Subassembly Measured Performance .................................................. 75 Final Amplifier Subassembly Measured Performance .................................................... 94 Full-System