Electromagnetic waves excitation by vibrator-slot structure in rectangular waveguide

The electromagnetic fields around a cylindrical boundary of variable curvature and surface impedance are expressed in terms of a complete set of local cylindrical modes, and Maxwell's equations are converted into coupled differential equations for the forward and backward wave amplitudes. The local cylindrical modes are shown to merge with the Fourier type expansion of the fields over plane surfaces. As an illustrative example, the launching of a surface wave over an infinite wedge with a rounded corner is considered in detail.

The problem of electromagnetic wave excitation by a vibrators system with variable distributed surface impedance located in free space is solved by the generalized method of induced electromotive forces (EMF). The characteristics of three-element and multi-element Yagi-Uda antennas with variable impedance vibrators are calculated.

Rectangular waveguide slot arrays are commonly used in several microwave antenna systems. The slots are most often located in the broad wall of the rectangular waveguide, arranged longitudinally parallel with the waveguide axis, because this provides good control of the excitation of each slot over a large dynamic range by adjusting the offset of the slot from the center line of the waveguide. However, longitudinal slots can only radiate electrical fields that are transversely polarized with respect to the waveguide axis. If longitudinal (or dual) polarization is required, the slots (or half of them) must be located transverse to the waveguide axis. Transverse resonant slots in the broad wall are too strongly excited for use in large arrays, so transverse narrow slots in the narrow wall are preferred. In the latter case the slots are not excited unless they are tilted or coupled to tilted parasitic elements like wires or posts inside the waveguide. The purpose of the present paper is to analyse an untilted narrow wall slot excited by two tilted wires. An improved and extended analysis in which the slot extensions into the neighboring two broad walls are included, is described. The virtual cylinder method is applied to the calculation of the external admittances of the slot using wedge dyadic Green's functions and entire-domain basis functions in order to get good convergence of the integrals of the spectral domain formulations.

The problem of electromagnetic waves radiation by a longitudinal slot in the broad wall of a rectangular waveguide is solved. The slot is radiating into half space above a perfectly conducting plane in the presence of two passive vibrators (monopoles) having variable distributed surface impedance in the space above the plane.

The photonic integrated circuits can be designed by analyzing optical waveguide structures with different types of gratings. The periodic coupling is analyzed for these waveguide structures using coupled mode theory, for both phase matched and non-phase matched conditions. The variations of coupling lengths based on refractive indices differences, operating wavelengths and separation between waveguides are analyzed and obtained the results. The difficulties of integrating the available optical components, which are in all fiber form, in photonic integrated circuits are conquered by these couplers. Integrated optics provides a solution to integrating these components on a single substrate, which miniaturizes the component. By analyzing different waveguide structures, components like optical couplers, wavelength filters, power dividers, polarization transformers etc. can be designed. This paper proposes rectangular, triangular and sinusoidal ridge waveguide structures that act as optical couplers, which provide better coupling efficiency.

The use of mechanic waves for assessing structural integrity is a well-known non-destructive technique (NDT). The ultrasound applied in the guided wave in particular requires significant effort in order to understand the complexities of the propagation so as to develop new methods in damage detection, in this case, knowing the interaction between the wave propagation and the geometry of the waveguides is mandatory. In the present work, the wave propagation in rectangular steel rod is presented. In this study, the section dimensions were fixed as 5 × 15 [mm], a typical element of the flexible riser structural amour commonly used in the offshore oil industry. The studies here presented were restricted to [0, 100 KHz] frequencies. This frequency interval is in the range of commercial waveguide equipment commonly applied in ducts in NDT applications. The computation of the dispersion curves is performed by using three different methodologies: (i) analytical solutions, (ii) a method that combines analytical approaches with finite element methods (SAFE), and (iii) experimental method that extracted information from the rod using laser vibrometers and piezoelectric actuators. Finally, two applications based on the dispersion curves determined in the rectangular waveguide are presented to illustrate the possibilities of the curve dispersion knowledge related to the specific geometry in the development and application linked to NDT. The first application consists on showing the possibilities of the techniques that use a fiber grating Bragg cell (FGB) to measure the wave displacement and the second application involves the simulation of pre-fissured prismatic waveguide aimed at searching to induce three characteristic acoustic events. The model was built combining the finite element method and a version of the discrete element method.

In this letter, we adopt a new procedure in the calculation of the layered Green's functions in the rectangular waveguide structure. In this procedure, the surface-wave poles are extracted first, and then the generalized pencil-of-function (GPOF) method is applied to approximate the spectral-domain Green's function along the real axis of the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$k_{\rho}$</tex> </formula> plane directly. Because no branch point is introduced in this procedure, improvement can be achieved compared to the traditional discrete complex image method (DCIM). In order to make this procedure more accurate and robust in both near- and far-field regions, a specially devised multiple-times GPOF procedure is applied to approximate the spectral-domain Green's function. Numerical results in this letter demonstrate the accuracy of our method.

Simulations of an energy dechirper based on dielectric lined waveguides

The GIDMULT algorithm (Z. Sipus et al, Appl. Comp. EM Soc. Journ., vol.13, no.3, p.243-254, 1998.) was used to investigate rectangular waveguide structures with finiteness in both transverse coordinates. Conventionally, the approach is unable to treat the finiteness of the side walls. This is circumvented by predefining the phase constant along the finite coordinate defining the walls, and then performing a numerical search for the modal propagation constant associated with field maxima. The particular rectangular waveguide configuration studied in this work was the dielectric-loaded hard E-plane walled rectangular waveguide. The GIDMULT-generated solutions agree well with those obtained analytically, validating this method and its flexibility. This technique was also used to study how the transverse field distribution over the guide cross-section varies with deviation of operating frequency from the TEM frequency. It was observed that the TEM frequency serves as a cutoff for surface waves along the dielectric slab.

Electromagnetic wave excitation by a given nonsymmetric source in the presence of a semi-infinite gyrotropic cylinder located in free space is considered. The source-excited field and the field scattered by the end of the cylinder are represented using eigenfunction expansions that refer to the respective regions on both sides of the cylinder endface. The distribution of the radiated power over the spatial spectrum of the excited waves is numerically analyzed.

We consider the possibility of electromagnetic wave generation in a plasma with ωPe>ωBe by “tail” electrons which scatter on anomalous Doppler resonance of potential waves with ω2≦ωBe. These oscillations, organized into periodic waves, resonantly excite potential waves of harmonic frequencies ω1=s·ω2≧ωPe, s=2, 3, .., easily transformable to electromagnetic radiation. A coherent mechanism for solar radio flares is developed.

Electromagnetic wave excitation is analyzed on a metal-backed ferrite thin sheet magnetized in the plane by a current source placed parallel to the magnetic field. Not only magnetostatic modes as propagating modes, but also evanescent, leaky and radiation modes are excited. The propagation factor, attenuation factor, equi-phase surface, equi-amplitude surface and electric field intensity of each mode are derived. Since this structure has a non-reciprocal character by virtue of the applied static magnetic field, non-reciprocity of those modes is explained in detail.

For of applications of waveguide-slot antennas, it is important to know the radiation characteristics of the slot in a rectangular waveguide wall radiating into a parallel-plate waveguide (PPW). In this work the properties of a longitudinal slot in the narrow wall of a rectangular waveguide radiating into a PPW are investigated. A model of a waveguide-slot radiator is presented and an accurate mathematical analysis provided. It is shown how to improve and optimize the matching of the considered radiators.

Tunable uniform field enhancement in a subwavelength air pillar by photonic doping in epsilon-near-zero medium

A novel double-ridged slot array antenna on the broad side of a single-ridged rectangular waveguide has been developed. The design is based on using a single-ridged waveguide as a series feed for an array of transverse slot radiators located along its broad wall. The main lobe radiation direction is 60 degrees and the gain is 10 dB. The waveguide broadwall dimension that is needed for the main lobe direction is 25% smaller than that for the rectangular waveguide. The main lobe scanning as a function of frequency is +or-2 degrees and the antenna standing wave ratio is better than 1.62:1 over the 5% bandwidth. >