Studies on microelectromechanically tuneable high-impedance surface for millimetre wave beam steering

    Research output: ThesisDoctoral ThesisCollection of Articles

    Abstract

    This thesis focuses on the development of novel microelectromechanically tuneable high-impedance surfaces (HIS) for millimetre wave beam steering applications. Microelectromechanical systems (MEMS) provide good functional parameters, e.g., low loss even at millimetre wave frequencies and excellent reliability, and can effectively compete with conventional technologies, e.g., ferroelectrics and ferrites. At the same time MEMS enable tuneability of the HIS, which can be used for developing reconfigurable devices with decreased system complexity, high level of integration and even as a system-on-a-chip, which dramatically reduces cost of the high frequency devices. The proposed MEMS tuneable HIS consists of a two-dimensional periodical arrangement of MEMS varactors, with a period much smaller than the wavelength of the interacting electromagnetic field, placed on an electrically thin grounded dielectric substrate. Being embedded in a waveguide, the structure can be used as an analogue type phase shifting element controlled by a bias voltage connected to the MEMS varactors. Alternatively, the MEMS tuneable HIS can be used as a smart electronic beam steering reflective surface, if a reconfigurable gradient of the effective surface impedance is induced throughout the structure by applying different programmed bias voltages to the different rows of the MEMS varactors. The methodology used in this study is a combination of analytical analysis, numerical simulations and electromagnetic measurements. A precise analytical model of the MEMS tuneable HIS is derived and used for designing of the structures operating in the W-band. Numerical simulations of different types of HIS and phase shifters based on the tuneable impedance surface embedded in rectangular metal waveguides and dielectric rod waveguides are carried out. Results of the numerical simulations correspond very well with the analytical calculations. Several prototypes of the multi-layered and MEMS-based HIS are fabricated and characterised. Measurements of the reflection coefficient show clear resonant high-impedance behaviour in the designed frequency range with reflection phase changing from almost 180° at lower frequencies to 0° at the resonance and to almost 180° at higher frequencies. The measured phase shifter based on a MEMS tuneable HIS placed adjacent to a dielectric rod waveguide exhibits an analogue type phase shift of up to 70° when the bias voltage is applied to the MEMS varactors.
    Translated title of the contributionStudies on microelectromechanically tuneable high-impedance surface for millimetre wave beam steering
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Räisänen, Antti, Supervising Professor
    • Räisänen, Antti, Thesis Advisor
    Publisher
    Print ISBNs978-952-60-4389-0
    Electronic ISBNs978-952-60-4390-6
    Publication statusPublished - 2011
    MoE publication typeG5 Doctoral dissertation (article)

    Keywords

    • high-impedance surface
    • artificial electromagnetic materials
    • microelectromechanical systems
    • MEMS
    • beam steering
    • phase shifters
    • millimetre wave

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