Bernice M. Dillon

Applied field/frequency response of planar gyromagnetic discs

Gyromagnetic resonators may be biased below, above or at the applied magnetic field required for ferrimagnetic resonance. A rigorous applied field/frequency solution for a planar disc is presented here by using a continuous model of material magnetization for these three regions of magnetic bias. The nonlinear relationship between the classic tensor entry description and the applied field/frequency parameters is established. Good agreement between calculated and measured resonances are also recorded.

Analysis of partial-height ferrite-slab differential phase-shift sections

Rectangular waveguide loaded with transversely magnetized ferrite slabs is a classic arrangement used in the construction of high-power differential phase-shift circulators. The characterization of this structure is extended in this paper by using a combined magnetostatic/microwave finite-element method to evaluate propagation characteristics in terms of material parameters, frequency, and bias field. Magnetic flux density was found to vary by typically 20% across a partial-height ferrite slab. Experimental phase-shift data agreed to within 5% of numerical calculations for a 9.25-GHz device. Supplementary design data are presented for the first higher order mode in the cutoff plane, the effect of material properties on phase shift, and to compare below and above resonance operation.

Split frequencies in planar axisymmetric gyroelectric resonators

Axisymmetric gyroelectric disk, ring, and composite resonator structures have been characterized for both InSb and GaAs semiconductors at 77 K. The calculations assume that these materials can be represented by the tensor permittivity derived from the Drude model of cyclotron motion in a plasma. Resonance and loss regions are identified and the sensitivity of normal mode splitting and onset frequencies to material and geometrical variables are graphed and tabulated. The information is presented in terms of signal frequency and the bias field to permit a direct comparison with results from ferrimagnetic structures. Semiconductor calculations show two extraordinary wave resonances and predict excellent symmetrical wide-band normal mode splitting. Field plots for the semiconductor disk and ring are included to explain coupled mode behaviour between modes in different bias regions.

Microwave and thermal analysis of a high-power ferrite phase shifter

Current radar applications require the design of high-power, differential phase shift ferrite circulators with increased bandwidth and better thermal performance. To meet these requirements, a magnetostatic/microwave/thermal method is proposed to model high-power ferrite devices. Magnetic losses are included in the model, which also has a temperature-dependent saturation magnetization and thermal conductivity. An iterative approach has been implemented which uses the power dissipated by the magnetic losses as the heat source for a thermal finite-element solver. Bias field, frequency, magnetic losses, and magnetization are used to determine the temperature profile in the ferrite for a given input power. The recommended operating region for temperature stability in high-power differential phase shift devices is deduced to be below subsidiary resonance and above low field loss.

Phase shift calculations in axially-magnetized ferrites using the finite element method

A vector finite element solver is used to calculate the phase shift in uniform axially magnetized gyromagnetic waveguides. Ferrite characteristics are specified in terms of the applied field, frequency, and material characteristics, including saturation magnetization and data from the hysteresis curve. Periodic boundary conditions are used to reduce the size of the meshed region. Calculations are compared with experimental results for two typical waveguide cross-sections: a quadruple-ridge Faraday rotation section and a reciprocal Reggia-Spencer section.<<ETX>>

Applied field/frequency dependency of propagation in axially magnetized ferrite waveguides

Vector finite-element solvers are used to calculate the phase shift in uniform axially magnetized gryomagnetic waveguides. Ferrite characteristics are specified in terms of the applied field, frequency, and material characteristics, including saturation magnetization and data from the hysteresis curve. Periodic boundary conditions are used to reduce the size of the meshed region. Calculations are compared with experimental results for two typical waveguide cross-sections: a quadruple-ridge Faraday rotation section and a reciprocal Reggia-Spencer section. >

Novel general finite element solver for gyroelectric structures

A novel general finite element solver for gyroelectric structures is presented. The solver is validated and compared with known gyrotropic waveguide solutions. Slab loaded semiconductor waveguides are investigated for nonreciprocity and differential phase shift is calculated. The proposed structures can potentially be exploited as nonreciprocal phase shift and control components for terahertz frequencies.

Nonuniform magnetization in microwave ferrite components by finite element analysis

Nonuniform magnetization occurs in nonellipsoidal ferrite shapes such as rectangular slabs used in microwave phase shift and control components. A finite element magnetostatic solver is used here to develop modified slab shapes, which reduce high magnetic flux concentrations in the corner regions. Microwave finite element calculations show that similar phase shift performance is obtained in the standard and modified geometries. The proposed differential phase shifter cross sections should increase operating bandwidths and provide better stability in high-power devices.

Bias-field/frequency design charts for composite gyrotropic resonators

The permeability and permittivity tensors of magnetised ferrite and semiconductor materials have different dependencies on bias field, signal frequency and material properties. Mode charts are presented for composite planar ring resonator junctions: the semiconductor case has an additional resonance region and exhibits more symmetrical split frequencies than the ferrite.

Variational solution of microwave circuits and structures

A unified variational formulation for microwave planar transmission lines and lumped-element impedances is developed and applied to an isolated stripline power splitter. Scattering parameters are calculated via the transfinite-element method and the numerical results are corroborated by three-port experimental measurements. The microwave impedance of a thin-film isolation resistor is separately measured and included in the model.