Date of Graduation

12-2025

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering (MSEE)

Degree Level

Graduate

Department

Electrical Engineering

Advisor/Mentor

Mantooth, Homer

Committee Member

Dix, Jeff

Second Committee Member

Di, Jia

Third Committee Member

Wu, Jingxian

Keywords

Beamforming; GaN; MMIC; Phase Shifter; Phased Array; True Time Delay

Abstract

This thesis presents the design, implementation, and high-temperature characterization of Gallium Nitride (GaN) monolithic microwave integrated circuits (MMICs) developed for beamforming and phased-array systems operating in the Ku-band (12-14 GHz). Two integrated circuits were designed: a 3-bit digital phase shifter and a 3-bit true time delay (TTD), both optimized for high linearity, low insertion loss, low phase error, and stable operation at elevated temperatures up to 300°C. Developing both a phase shifter and a TTD enabled a direct comparison of their beamforming performance and the evaluation of beam squint effects over frequency, a critical factor in wideband array design. The circuits were implemented in a 0.15µm GaN-on-SiC process and designed using modular switch and delay cell architectures. To evaluate their performance under high-temperature conditions, custom test boards were fabricated on an Alumina substrate. The test setup included on-board SOLT calibration standards, SMA connectors for RF interfaces, and a DC power supply to control the switching of each control bit. Thermal characterization was conducted using a thermocouple and a temperature-controlled chuck capable of reaching 300°C. Measured S-parameters, phase shifts, and time delays confirm stable and repeatable operation across the desired temperature range, demonstrating the feasibility of GaN-based phase shifters and true time delay circuits for high-power, high-temperature phased-array applications such as radar and satellite communication systems. The results highlight the robustness and thermal reliability of GaN MMIC technology for extreme-environment RF front-end systems and provide comparative insight into the trade-offs between phase shift and true time delay architectures with respect to beam squint and broadband beamforming performance.

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