Vincent G. Harris, Anton L. Geiler
Date of Award
Doctor of Philosophy
Department or Academic Unit
College of Engineering, Department of Electrical and Computer Engineering
electrical engineering, circulator, microstrip, microwave
Electrical and Computer Engineering
Circulators are important components in modern radar systems. Its non-reciprocal chracteristics make it possible for the radar systems to receive and transmit the signals at the same time and same frequency. However, bulky permanent magnets are required to provide a large static magnetic field in order for the traditional circulator to function properly. This thesis focuses on how to remove the permanent magnets so that size, weight and cost of systems can be reduced.
In-plane circulator requires low-biasing field due to the shape anisotropy of the magnetic substrate. This thesis presents a spectral domain method to assist the analysis of magnetic microstrip line and magnetic coupled microstrip lines. The latter is the main component of the in-plane circulator. The ferrite modeled by this method could be cubic , M-type , Y-type and Z-type ferrites. An in-plane circulator based on YIG(yttrium iron garnet) operating at C band is designed with this method and simulated with Ansoft® HFSS. The reflection and isolation is less than 15 dB from 6.3 GHz to 7.8 GHz with a 200 Oe biasing field.
A self biased junction circulator based on oriented M-type hexaferrite was designed, fabricated and tested. A new topology structure was used to ease the fabrication process and integration with other components. An isolation of 21 dB with corresponding insertion loss of 1.52 dB was measured, which render itself to the first hexaferrite-based self-biased circulator operating below 20 GHz.
Theoretical models were developed to design self-biased Y-junction circulators operating at UHF frequencies. The proposed circulator design consisted of insulating nanowires of YIG embedded in high permittivity BSTO(barium-strontium titanate) substrates. The model represents the nanowires and the BSTO substrate by an equivalent medium with effective properties inclusive of the average saturation magnetization, dynamic demagnetizing fields, and permittivity. The effective medium approach was validated against the exact calculations and good agreement was observed between the two simulations in terms of calculated S-parameters. Using the proposed approach, a self-biased junction circulator consisting of YIG nanowires embedded in a BSTO substrate was designed and simulated. The center frequency insertion loss was calculated to be as low as 0.16 dB with isolation of -42.3 dB at 1 GHz.
Wang, Jianwei, "Toward self-biased ferrite microwave devices" (2011). Electrical Engineering Dissertations. Paper 37. http://hdl.handle.net/2047/d20001032
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