Date of Award

6-2026

Degree Name

MS in Electrical Engineering

Department/Program

Electrical Engineering

College

College of Engineering

Advisor

Payam Nayeri

Advisor Department

Electrical Engineering

Advisor College

College of Engineering

Abstract

Millimeter-Wave (mm-wave) technology utilizes high frequency spectrum and can deliver multi-gigabit speeds, ultra-low latency, and massive bandwidth capacity. However, this technology is rather new and many technical challenges remain. On the other hand, Reconfigurable Intelligent Surfaces (RIS) have emerged as promising structures for controllable electromagnetic wavefront manipulation in wireless communication systems. This thesis presents the design of a 2-bit RIS unit-cell element operating throughout the 30–34 GHz mm-wave band, where the structure was progressively refined from an initial resonating geometry toward a grounded reflective RIS configuration. The proposed structure utilizes PIN-diode switching states to produce four discrete reflected phase states with approximately 90◦ phase separation between adjacent states, collectively approaching full 360◦ reflected phase coverage required for programmable reflected wavefront manipulation. The proposed RIS element shows a reflection loss of better than 0.5 dB across the band, while the reflected phase states exhibit less than 6◦ phase error at the 32 GHz design frequency.

Oblique angle studies showed that the reflected phase shift varies between 10◦ to 30◦ as the incident wave direction changes from 0◦ to 30◦. This is due to the strongly resonant behavior required for RIS operation which introduces increased sensitivity to oblique excitation conditions. As a potential solution to improve angular stability, a multilayer Frequency Selective Surface (FSS) superstrate synthesized through coupled interdigital capacitive and inductive strip layers was also studied. The proposed FSS demonstrated superior performance in reducing sensitivity to oblique angles up to 45◦ as a stand-alone surface. The integrated cascaded RIS-FSS configuration was subsequently investigated under oblique excitation conditions, where electromagnetic coupling effects were observed to alter the reflected phase response of the multi- state RIS operation following integration. These observations show that neighboring resonant electromagnetic surfaces cannot be cascaded independently without careful consideration of the coupling interactions introduced following integration.

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