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Ferroelectric microwave circuits

Cheng, Leong Ching (2009)
Ph.D. thesis, University of Birmingham.

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Abstract

Ferroelectric materials have been found to be particularly attractive materials for the development of tunable microwave devices over the past few decades due to their distinctive characteristic that is the variation of dielectric constant as a function of electric field. In this research project, the work on how the finite difference method (FDM), a computational technique, is modified to suit the evaluation of the cross-sectional field distribution of a ferroelectric-based transmission line is presented and the results are verified. The modified FDM was employed for determining the effective dielectric constant (Ɛeff) and the characteristic impedance (Zc) of ferroelectric-based structures where the spatial variation of dielectric constant was taken into consideration.
A significant portion of this research is focused on the application of ferroelectric materials in designing tunable microwave devices. Two optimised phase shifters incorporating Barium Strontium Titanate (Ba0.5Sr0.5TiO3 or BST) ferroelectric thin-films are designed, fabricated and measured. One is based on simple coplanar waveguide (CPW) transmission line, and another is based on tapered CPW structure.
To date, no work on tunable attenuator using ferroelectric materials has ever been reported, as contrary to other extensively studied ferroelectric-based tunable microwave devices, namely tunable resonators, filters, and phase shifters. In this work, a novel design of tunable attenuator integrating BST thin-films is presented and verified with experimental results from a similar design of tunable attenuator based on Roger/Duroid 6010LM substrate of dielectric constant 10.2. The application of ferroelectric thin-films enables continuous variation of attenuation under controlled bias voltages with significant size and weight reduction in the overall device.

Type of Work:Ph.D. thesis.
Supervisor(s):Lancaster, M.J.
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Electronic, Electrical and Computer Engineering
Subjects:TK Electrical engineering. Electronics Nuclear engineering
Institution:University of Birmingham
ID Code:6578
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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