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Title: Miniature YBCO/MgO planar superconducting filter, oscillator and delayline structures
Author: Terry-Wood, S.
Awarding Body: University of Portsmouth
Current Institution: University of Portsmouth
Date of Award: 2005
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The design of practical high performance radio frequency and microwave frequency circuits employing high transition temperature superconductors is presented. High quality factor resonators and very low insertion loss bandpass filters constructed using the high temperature superconductor YBCO with a transition temperature of 87 Kelvin are described. These very high quality factor energy-trapping shielded microstrip cavity structures employed a very low loss MgO dielectric substrate with YBCO superconducting ground plane, strip plane, shield plane and normal metal end walls. This structure was analysed to reveal the allowed modes in each region of the planar cavity structure so that critical dimensions could be selected to confine electromagnetic fields closely to the strip structures and away from the lower quality factor normal metal end walls. The distance away from the normal metal cavity end walls where a microstrip structure does not experience quality factor degradation due to TE and TM mode reflections from the lossy end walls was calculated. This calculation was carried out for Silver, Gold and Titanium end walls. The synthesis of YBCO/MgO shielded microstrip realizable bandpass filter structures, without bridge and through-hole connections, is described. H resonator filter structures constructed from coupled and uncoupled straight lines were investigated. Miniature meander filter structures constructed from meander lines and meander gap structures were also investigated. Four examples of miniature very low insertion loss shielded microstrip bandpass filters employing H resonators and meander resonators operating in the VHF-UHF-SHF frequency range were designed and constructed. Measured frequency responses for these superconducting filters were compared with electromagnetic simulations. The synthesis of YBCO/MgO shielded microstrip realisable oscillator circuits, without bridge and through hole connections, is described. A cryogenically cooled GaAs FET VHF oscillator using a compact YBCO superconducting spiral resonator was designed and constructed. This common drain Clapp oscillator circuit configuration was analysed to reveal optimum component values for low phase noise 111 operation. Measurements of output power spectrum and simple phase noise measurements were carried out in order to evaluate the performance of this oscillator. A novel dual meander delay line structure is presented. An example dual meander delay line was designed and constructed in a superconducting YBCO/MgO shielded microstrip cavity structure. This novel delay line structure was shown by electromagnetic simulation to exhibit superior performance when compared to an equivalent single meander line in the same substrate area. This improved delay line structure was demonstrated to operate over a wider bandwidth and exhibit lower dispersion than the equivalent single meander line. The measured performance for the superconducting dual meander delay line was compared with electromagnetic simulations for ideal single and dual meander structures.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available