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MODULAR FREQUENCY MULTIPLIER AND FILTERS FOR THE GLOBAL HAWK SNOW RADAR

Hara Madhav Talasila – University of Kansas

Defended January 20, 2017

Remote sensing with radar systems on airborne platforms is key for wide-area data collection to estimate the impact of ice and snow masses on rising sea levels. The NASA P-3B and DC-8, as well as other platforms, successfully flew with multiple versions of the Snow Radar developed at the Center for Remote Sensing of Ice Sheets. Compared to these manned missions, the Global Hawk Uninhabited Aerial Vehicle can support flights with long endurance, complex flight paths and flexible altitude operation up to 70,000 ft. This thesis documents the process of adapting the 2-18 GHz Snow Radar to meet the requirements for operation on manned and unmanned platforms from 700 ft to 70,000 ft. The primary focus of this work is the development of an improved microwave chirp generator implemented with frequency multipliers. The x16 frequency multiplier is composed of a series of x2 frequency multiplication stages, overcoming some of the limitations encountered in previous designs. At each stage, undesired harmonics are kept out of the passband and filtered. The miniaturized design presented here reduces reflections in the chain, overall size, and weight as compared to the large and heavy connectorized chain currently used in the Snow Radar. Each stage is implemented by a drop-in type modular design operating at microwave and millimeter wavelengths; and realized with commercial surface-mount integrated circuits, wire-bondable chips, and custom filters. DC circuits for power regulation and sequencing are developed as well. Another focus of this thesis is the development of the band-pass filters used in the frequency multiplier using different distributed element filter technologies. Multiple edge-coupled band pass filters are fabricated on alumina substrate based on the design and optimization in computer-aided design tools. Interdigital cavity filter models developed in-house are validated through full-wave iv electromagnetic simulation and measurements. Overall, the measured results of the modular frequency multiplier and filters match with the expected responses from original design and cosimulation outputs. The design files, test setups, and simulation models are generalized to use with new designs in the future.