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Title: Composite materials for microwave frequency agile planar devices
Author: Mills, John Brean
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2003
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The potential of Calcium-Vanadium garnet loaded binary composites for use in the production of planar frequency agile microwave devices has been investigated. A WR90 rectangular waveguide system using the transmission/reflection technique has been used to compare effective medium theory predicted permittivities and permeabilities for unmagnetised and transversely magnetised composites with actual measured composite properties. Use of the the Bruggeman effective medium theory with manufacturer supplied garnet permittivity and values of garnet permeability calculated using simple empirical models were demonstrated to be as accurate as predictions made using the measured properties of the composites' individual constituents. Errors in predicted material properties for unmagnetised and transversely magnetised samples relative to measured data were less than 5% across almost half of the 8.2 -12.4GHz measurement band and within a worst-case error of 15% across the whole band. A series of end-coupled linear microstrip resonators using garnet-loaded composite substrates has been fabricated and tested. Tunabilities in resonance of up to 3.9% at 9.2GHz have been demonstrated for DC magnetic bias fields applied transverse to the microwave magnetic field component. An entirely new and previously unpublished broadband microstrip technique for the measurement of the effective permittivity and permeability of bulk gyromagnetic and gyromagnetic material loaded composite substrates subject to transverse DC magnetic bias fields is presented. This will have wide application in the design of frequency agile microwave integrated circuits.
Supervisor: Edwards, David ; Stevens, Chris ; Dew-Hughes, David Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Engineering & allied sciences ; Communications engineering (optical,microwave and radio) ; microwave ; composite materials ; permittivity ; permeability