摘要:

A fully nonlinear theory of the magnetron is presented starting from the equations of classical electrodynamics. A crucial step in the development is an orthogonal-series expansion of the space charge and current densities using appropriate sets of cavity modes, the expansion coefficients being nonlinear functionals of the electron trajectories. Splitting the electric field vector into its solenoidal and irrotational (gradient of a scalar potential) parts, expanding the magnetic field and the solenoidal part of the electric field in a complete set of orthonormal solenoidal cavity modes, and substituting these expansions into Maxwell's equations, differential equations governing the time evolution of the mode amplitudes are derived. These differential equations for the mode amplitudes and the Poisson's equation for the scalar potential are solved in terms of the charge and current densities in the interaction region. Substitution of the explicit expression for the field components in terms of the charge and current densities into the equations of electron motion reduces the latter to a fixed-point problem for a vector nonlinear operator in an appropriate function space. The fixed point, and hence the solution for the oscillatory fields inside the magnetron, may be found by standard successive approximation techniques. For the special case of a smooth-anode magnetron (magnetron diode) the mode-amplitude equations are completely solved to yield the initial growth of the mode amplitudes. It is seen from this solution that as soon as the electrons are made to follow a curved path leading to a nonzero azimuthal current in the magnetron cavity, oscillations start to build up from a zero initial value. Thus it is seen, contrary to the conclusions of the current theories of the magnetron, that it is totally unnecessary to assume, a priori, the presence of any kind (random or deterministic) of high-frequency disturbances initially in the cavity to explain the build-up phenomenon. The detailed study of oscillation build-up based on the successive approximation solution for the electron trajectories will be deferred to the second part of this contribution.

ISSN:0920-5071    

DOI:10.1163/156939392X00012

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The method of separation of variables is used to derive an analytic solution to the problem of electromagnetic scattering by a homogeneous dielectric spheroid with a confocal lossy dielectric coating of arbitrary thickness. The electric and magnetic fields in each different region are expressed in terms of a set of vector spheroidal eigenfunctions, and the solution is obtained by imposing the appropriate boundary conditions at each spheroidal surface. Computed results illustrate the dependence of the scattered field in the far zone on the coating material and its thickness, the size and the material of the spheroid, and on the angle of incidence.

ISSN:0920-5071    

DOI:10.1163/156939392X00021

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Localized electromagnetic focused heating from a finite rectangular aperture antenna array into a lossy medium is considered in a quantitative manner. The general prescription for focusing the electric field components is given. In particular, two types of focusing are presented that have applications in hyperthermic cancer therapy and geophysical sub-surface probing. It is shown that, for low loss tangents, the focusing can be very sharp but it deteriorates significantly for higher loss (e.g., for loss tangents greater than 0.20).

ISSN:0920-5071    

DOI:10.1163/156939392X00030

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In this paper propagation of transient electromagnetic waves in a reciprocal bi-isotropic medium is presented. The constitutive relations are convolution integrals with two susceptibility kernels that model the medium. The propagation problem is solved by the introduction of a wave-splitting technique. This wave-splitting is used to solve the propagation problem using either an imbedding approach or a Green's function technique. In particular, the scattering problem of an electromagnetic wave that impinges normally on a slab of finite or infinite extent is solved. The slab is assumed to be inhomogeneous with respect to depth. The scattering problem consists of finding the reflected and the transmitted fields and the generic quantities are the reflection and the transmission kernels of the medium. Explicit expressions for the rotation and the attenuation of the wave front is presented for the inhomogeneous slab. In the special case of a homogeneous infinite slab it is proved that the reflection kernel satisfies a nonlinear Volterra equation of the second kind, very suitable for numerical calculations. It is also proved that no cross polarization contribution appears for the homogeneous slab. Several numerical computations illustrate the analysis.

ISSN:0920-5071    

DOI:10.1163/156939392X00049

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A review of a recursive algorithm with a more succinct derivation is first presented. This algorithm, which calculates the scattering solution from an inhomogeneous body, first divides the body into N subscatterers. The algorithm then uses an aggregate T matrix and translation formulas to solve for the solution of n+1 subscatterers from the solution for n subscatterers. This recursive algorithm has reduced computational complexity. Moreover, the memory requirement is proportional to the number of unknowns. This algorithm has been used successfully to solve for the volume scattering solution of two-dimensional scatterers for Ez-polarized waves. However, for Hz-polarized waves, a straightforward application of the recursive algorithm yields unsatisfactory solutions due to the violation of the restricted regime of the addition theorem. But by windowing the addition theorem, the restricted regime of validity is extended. Consequently, the recursive algorithm with the windowed addition theorem works well even for Hz-polarized waves.

ISSN:0920-5071    

DOI:10.1163/156939392X00058

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The phenomena occurring in gyromagnetic guides in the presence of two propagating modes are analyzed using the coupled mode method. It is found that the superposition of these modes results in the periodic transfer of electromagnetic field energy across the guide. Depending on the structure symmetry with respect to the biasing field orientation, the oscillation period may or may not depend on the propagation direction, but the effect itself has always the nonreciprocal character. It is also found that unlike in the isotropic structures, the difference in phase velocities of guided modes is not a sufficient condition for the energy transfer to occur. The results of the analysis are applied to derive the scattering matrices of a section of asymmetrical structure of two parallel guides coupled via a ferrite medium.

ISSN:0920-5071    

DOI:10.1163/156939392X00067

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Analytical expressions for the resonant frequencies in an electromagnetic cylindrical cavity with an internal off-axis electrically small sphere are derived, for both magnetic and electric modes. The walls of the cylindrical cavity and the small sphere are perfectly conducting. Cylindrical vector wave functions and related translational addition theorems, as well as expansion of cylindrical wave functions in terms of spherical ones, are used. The results are useful in problems connected with excitation or probing of resonant cavities. Some remarks are made about the best positioning of the probe, for more exact measurement of the resonant frequency of any mode in the empty cavity. Graphical results for some of the lower order modes are given, for various values of the parameters and for both kinds of modes.

ISSN:0920-5071    

DOI:10.1163/156939392X00076

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939392X00085

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939392X00094

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor