Plane-wave diffraction by a wedge--A spectral domain approach

The canonical problem of plane wave diffraction by a wedge in the context of the spectral domain approach which exploits the relationship between the induced current on a scatterer and its far field is investigated. It is shown how the exact solution to the wedge diffraction problem can be manipulated in a form which enables one to interpret the far scattered field as the Fourier transform of the physical optics (PO) current on the two faces of the wedge augmented by the fringe current near the tip of the wedge. A uniform asymptotic expansion for the total field which slightly modifies the Ansatz in the uniform asymptotic theory of electromagnetic edge diffraction is constructed.     

Research on spectral domain immittance approach

In this paper, we have obtained the equations of electrodynamics for a gyrotropic medium using the Maxwell's equations. Through the Fourier Transforms (FT), the admittances of TM and TE modes in the electrically gyrotropic substrate and the magnetically gyrotropic substrate are given. Then we can use the spectral domain immittance approach to analyse the finline structures with a gyrotropic medium. The propating characteristics of the dominant mode in magnetized-ferrite-loaded double-layered finlines are studied, numerical results are presented which could be used in designing a finline displacement isolator.     

Comments on "Wide-band diffraction improved dual-shaped reflectors"

It is pointed out that the procedure mentioned in the above paper need not be followed for dual-reflector systems using small subreflectors. In addition, a uniform procedure suitable for both large and small subreflector systems, is presented.     

Comments on "Comparison of three high-frequency diffraction techniques"

It is shown that the method of edge waves (MEW) [1] (or "physical theory of diffraction") describes the secondary edge waves correctly. Opposing statement found in [2]-[4] results from some misunderstanding. It is noted that both MEW and the geometrical theory of diffraction may predict, at best, only the first two terms in an asymptotic expansion (with k → ∞) of the sum of the edge waves for real three-dimensional bodies. Some formulas dealing with MEW in [1] are defined more precisely.     

A spectral domain interpretation of high frequency diffraction phenomena

A spectral domain interpretation of high frequency diffraction phenomena is discussed using the concept of a spectral diffraction coefficient, which resembles Keller's coefficients. The solution of the two-dimensional problems of diffraction of an arbitrary field (with no caustics) by a half-plane is investigated and results are given for any observation angle including, in particular, asymptotic determination of the field at the shadow boundaries. The high frequency scalar diffraction by apertures is formulated in a systematic manner and the formulation, which is valid for any observation angle, is compared with that of other techniques. Results are also given for the diffracted field at the caustics.     

Plane-wave scattering by a magnetoplasma cylinder

The scattering of H-polarised plane waves by an infinitely long axially magnetised cylinder of uniform plasma is investigated for the case in which the radius of the cylinder is small in comparison with the wavelength of the incident wave. The scattering amplitude is found to be a maximum at two frequencies, which are shown to be related to the familiar dipolar resonant frequency of an isotropic plasma column. Approximate expressions for the two resonant frequencies are derived.     

Modeling of discontinuities on lossy planar microwave structures by the spectral domain approach

New components appear, that require an improvement in the modeling methods in the microwave field. Indeed, in order to model the working of components such as the photoelectrical switch, whose substrate conductivity varies under the action of a judiciously chosen light beam, it has proved that taking losses in 3D problem was required. Thus, we have coupled the complex frequency concept to a dynamic modeling method: the spectral domain approach. This concept lays on the fact that the resonance frequency of a lossy resonator is complex. It enables to get the quality factor of the resonator and then its equivalent circuit, including the resistive elements that are characteristics of the losses. In the case of low losses, this general principle can be used through a perturbation method. We develop here this principle and use it for the study of a photoelectrical switch.     

Analysis of asymmetrical multilayer ferrite-loaded finlines by theextended spectral domain approach

The spectral domain approach is extended to analyze the nonreciprocal propagation characteristics of asymmetrical multilayer finlines containing magnetized ferrites. This extended method offers several advantages. It can be applied to nonuniform cross-section geometries, uses only one set of basis functions, and the dyadic Green's function is efficiently derived by a recursive algorithm. Fast convergence is obtained and the accuracy of the method is verified by comparison with available computed and measured data. In comparison with symmetrical structures, the additional design degree of freedom of the asymmetry can be used to obtain wider bandwidth and higher nonreciprocity. Of the various structures considered, a four-layer dual ferrite (DF) structure is seen to be the best choice for realization of nonreciprocal phase shifters with widest bandwidth     

Comments on "A uniform geometrical theory of diffraction for an edge in a perfectly conducting surface"

The edge diffraction coefficients of Kouyoumjian and Pathak, when applied to edges in curved screens produce discontinuities in the diffracted fields which do not coincide with those of the specular field on the concave side of the screen. In regions where coincidence occurs the discontinuities add, rather than cancel. The field calculated from the diffraction coefficient violates the principle of reciprocity.     

Light diffraction by biperiodic stripe domain structures

Results of theoretical and experimental investigation of magnetooptic light diffraction by biperiodic stripe domain structures are presented. Such structures exist in ferrite films made from uniaxial magnetic garnets with small positive anisotropy constants. Effects of an external magnetic field and of the film thickness on the symmetry of observed diffraction patterns and on the distribution of the light intensity in different diffraction maxima are studied. Changes in the symmetry of Fourier transforms are shown to occur during phase transitions between different types of biperiodic stripe domain structures. Theoretical calculations of the light intensity of diffracted radiation are shown to agree well with experimental data.     

Comments on spectral efficiency of VMSK

This article demonstrates that no ultra narrow band modulation (UNBM) method, which includes very minimum shift keying (VMSK) and VPSK, can have substantially greater efficiency than conventional methods, such as quadrature amplitude modulation (QAM), in transmission in the same frequency band     

Extended spectral domain approach for analysis of lossy cylindrical dielectric resonators

The spectral domain approach is extended for evaluating both the resonant frequency and Q factor of a lossy cylindrical dielectric resonator operating in TE/sub 0/ modes, taking into account the effects of conducting enclosure and supporting substrate. On the basis of the equivalence principle, the circular electric currents are introduced to simulate the fields inside and outside the cylindrical dielectric sample, which separates the original problems into two auxiliary structures with radially homogeneous multilayered dielectrics. Using the spectral immittance method in conjunction with the point-matching method, the characteristic equations are derived. The present technique has no need to determine the time-consuming, complex higher-order modes. Some typical examples are computed. The numerical results agree well with experimental data available in the literature.<>