AbstractMillimetre-wave nonreciprocal devices are vital elements in many modern radar and communication systems. Gyromagnetic behaviour in magnetised ferrite materials has been utilised for decades in the design of nonreciprocal devices. However, the effects of ferrite's limited saturation magnetisation and high loss as the frequency of operation exceeds 40 GHz render such devices inadequate for millimetre-wave applications. On the other hand, solid plasma (such as semiconductors) are known to exhibit gyrotropic behaviour when they are biased with a steady magnetic field. This behaviour (which is referred to as gyroelectric) can extend up to the THz frequency ranges. Hence, magnetised semiconductors can be regarded as suitable candidates for realising millimetre-wave, sub-millimetre-wave and even THz nonreciprocal devices. This thesis focuses on analysing different structures containing gyroelectric materials, and proposing millimetre-wave nonreciprocal devices based on the theoretical findings. Measurements and full wave electromagnetic simulation are used to validate and optimise the proposed designs where possible. Before starting the electromagnetic analysis, the physical properties of a semiconductor plasma are studied, then a permittivity tensor is introduced to include the microscopic features of the magnetised semiconductors into a macroscopic model. Different semiconductor candidates for gyroelectric designs are also discussed and analysed. Firstly, Semiconductor Junction Circulators (SJC's) are analysed using a Green's function approach. The same approach is then used to proposed new designs for broadband millimetre-wave SJC's that require low magnetic bias using Indium Antimonide (InSb) cooled down to 77 K. The possibility of realising planar nonreciprocal devices using a Molecular Beam Epitaxy (MBE) grown Two Dimensional Electron Gas (2-DEG) is also studied. Theoretical and simulation results prove the possibility of using this material to realise millimetre-wave resonators and circulators. Then a novel type of circulator is realised by placing an InSb disk at 77 K in the middle of a three port waveguide junction. The structure is analysed by treating the junction as a resonator with a suspended axially magnetised gyroelectric rod placed in the middle. Electromagnetic analysis, simulations and measurements reveal the existence of counter rotating modes that degenerate or split at certain frequencies under specific magnetic bias conditions. Measuring this circulator reveals an isolation of 18 dB at 38.5 GHz when the InSb disk is biased with a D.C. magnetic flux of 0.55 T. This is the first time such a circulator has been demonstrated theoretically and experimentally.In addition to the three port circulator, a model is developed for a rectangular waveguide loaded with layered dielectric and gyroelectric media. Mathematical analysis reveals the dispersion relations and field distributions for such a structure. High nonreciprocity in both phase and attenuation constants is observed from analysing a rectangular waveguide loaded with a transversely biased InSb slab at 77 K. The expected nonreciprocity is then verified, for the first time, by simulation and measurement of similar structures under the same conditions. More than 35 dB of isolation at f=35.6 GHz was obtained when loading a WR-28 rectangular waveguide with an InSb slab at 77 K, transversely biased with a magnetic flux of 0.8 T. Different effects on the isolation behaviour are also discussed theoretically and experimentally, including the effects of the slab's thickness and length, the magnetic bias and the existence of a dielectric layer above the gyroelectric slab. Theoretical and experimental outcomes of this thesis prove the possibility of using gyroelectric materials to develop a new class of component that meets the demands for millimetre-wave nonreciprocal devices. This will provide a significant improvement to the modern high frequency millimetre-wave systems.
|Date of Award||31 Dec 2016|
|Supervisor||Robin Sloan (Supervisor) & Mohamed Missous (Supervisor)|