Open Waveguide Research Articles

Comments on "Uniform ferrite-loaded open waveguide structure with CRLH response and its application to a novel backfire-to-endfire leaky-wave antenna"

In the above-named paper, a transversely magnetized ferrite open-waveguide has been analyzed. That paper demonstrated that a forward-to-backward TE guided-wave transition may occur as a function of either frequency or magnetostatic bias. It further demonstrated that a scanning leaky-wave antenna may be built from such a guide. Although the rigorous analysis of the β = 0 crossing presented there is laudable, it also contains a number of shortcomings that require clarification. The purpose of this comment is threefold. First, it will be shown that pertinent references appear to have been overlooked. Second, certain strong claims that are made in the original work must be properly placed in context. Third, it will be shown that losses have been inadequately assessed.

Periodic Leaky-Wave Antenna for Millimeter Wave Applications Based on Substrate Integrated Waveguide

Substrate integrated waveguides (SIW) are built up of periodically arranged metallic via-holes or via-slots. The leakage loss of SIW structures increases with the distance between the via-holes or via-slots. An open periodic waveguide with a large via distance supports the propagation of leaky-wave modes and can thus be used for the design of a leaky-wave antenna. In this paper, this leakage loss is studied in detail and used to design a periodic leaky-wave antenna. The proposed concept represents an excellent choice for applications in the millimeter-wave band. Due to its versatility, the finite difference frequency domain method for periodic guided-wave or leaky-wave structures is used to analyze the characteristics of the proposed periodic leaky-wave antenna. Two modes (TE10 and TE20) are investigated and their different leaky-wave properties are analyzed. Based on the proposed leaky-mode analysis method, a novel periodic leaky-wave antenna at 28-34 GHz is designed and fabricated.

ELECTRODYNAMICAL CHARACTERISTIC PARTICULARITY OF OPEN METAMATERIAL SQUARE AND CIRCULAR WAVEGUIDES

We present here the solution of the eigenvalue problems for the open metamaterial square and circular rod waveguides. The Maxwell's equations for the electrodynamical analysis of the open waveguides were solved by the Singular Integral Equations' (SIE) method and partial area method. Our SIE method is pretty universal and let us rigorously analyze open waveguides electrodynamically with any arbitrary cross-sections taking into account of the edge condition. The false roots did not occur applying the SIE method. The waveguide media can be of strongly lossy materials. The signs of the complex permittivity and permeability can be positive or negative in difierent combinations. We used our computer algorithms based on the two mentioned methods with 3D graphical visualization in the MATLAB language. We present here our numerical calculations of the metamaterial square waveguide with sides equal to 5 ¢ 10 i3 m and the metamaterial circular waveguide with the diameter equal to 5¢10 i3 m. We present dependences of phase constant and attenuation constant of metamaterial waveguides at the frequency range from 75GHz till 115GHz. We have compared the three dimension (3D) electric fleld distributions of the main mode and the flrst higher mode propagating in the square and circular metamaterial waveguides. The calculations of the electric flelds were fulfllled at approximately 10000 points in every cross-section. We discovered that the electric fleld is concentrated at the waveguide boundary. The distribution of the electric fleld along the perimeter of the waveguide is not uniform. There are two areas on the perimeter of the square and circular waveguides

A multimodal method for non-uniform open waveguides

We present an original method for the simulation of ultrasonic waves in a varying cross section elastic waveguide embedded in a homogeneous matrix. The so-called multimodal methods consist in expanding the acoustic field in each transverse section as a series which involves the modes of a perfectly cylindrical waveguide with this particular section. For such a cylindrical waveguide, the modal components of the acoustic field are uncoupled. But a varying cross section yields a coupling of these components. A multimodal approach consists in solving the system of differential equations which couples these components instead of the propagation equations.Such methods have been extensively studied for closed waveguides, that is, when no wave can radiate in the transverse direction. In our case, radiation waves occur, because of the presence of the matrix. Actually, such an open waveguide is characterized by a continuum of radiation modes together with a possible finite set of guided modes. The multimodal method proposed here does not take into account this continuum, but uses instead the concept of leaky modes. These modes appear naturally when the computational domain is artificially limited by Perfectly Matched Layers (PMLs). The main advantage of using leaky modes instead of radiation modes is that the formers compose a discrete set, which simplifies considerably the implementation of a multimodal method. In the case of a simple two-dimensional scalar model, the basic ideas of such a method are presented and illustrated by numerical results.

10.1007/s11487-008-1006-6

A rigorous analytic approach to solution of the problem of wave propagation through a plane transverse junction of two open waveguides is proposed. According to the method developed, the problem is reduced to a system of integral equations of the second kind, which is solved with the help of iterations. The use of the method is exemplified by its application to the problem for a coaxial junction of two circular metal/dielectric waveguides.

A Dual Passband Filter using Hybrid Microstrip Open Loop Resonators and Coplanar Waveguide Slotline Resonators

A novel dual passband filter using hybrid microstrip open loop resonators and coplanar waveguide (CPW) slotline resonators is proposed. With the CPW feeding structure, the center frequencies and 3-dB fractional bandwidth (FBW) can be achieved relatively independently. The external quality factor and coupling coefficient of the resonators are obtained. The proposed dual passband filter has center frequencies of 2.44 GHz and 3.5 GHz, which could be appropriately used for wireless local area networks (WLAN) and WiMax. Good agreement between simulated and measured results is demonstrated.

On the use of leaky modes in open waveguides for the sound propagation modeling in street canyons

An urban, U-shaped, street canyon being considered as an open waveguide in which the sound may propagate, one is interested in a multimodal approach to describe the sound propagation within. The key point in such a multimodal formalism is the choice of the basis of local transversal modes on which the acoustic field is decomposed. For a classical waveguide, with a simple and bounded cross-section, a complete orthogonal basis can be analytically obtained. The case of an open waveguide is more difficult, since no such a basis can be exhibited. However, an open resonator, as displays, for example, the U-shaped cross-section of a street, presents resonant modes with complex eigenfrequencies, owing to radiative losses. This work first presents how to numerically obtain these modes. Results of the transverse problem are also compared with solutions obtained by the finite element method with perfectly mathed layers. Then, examples are treated to show how these leaky modes can be used as a basis for the modal decomposition of the sound field in a street canyon.

Solution of the exterior boundary value problem of electromagnetic waves propagating in a dielectric waveguide with an arbitrary cross section

A method is proposed for solving the boundary value problem of electromagnetic waves propagating in an open dielectric waveguide with an arbitrary cross section. The method combines the representation of solutions in the form of a continuous spectrum, the Fourier integral method, and the Galerkin variational procedure.

Generalized Simple Theory for Estimating Lateral Leakage Loss Behavior in Silicon-on-Insulator Ridge Waveguides

In this paper, we numerically investigate the lateral leakage loss behavior for TM-like modes in silicon-on-insulator ridge wave guides. If the waveguide width is set to satisfy a certain condition, the leakage loss of the TM-like mode leads to be a minimum. When utilizing TM-like modes in the ridge wave guides, it is the main drawback that the tolerance for the variations in the waveguide width and operation wavelength is too small. In this paper, we propose a novel ridge waveguide structure, where a dimple is introduced at the ridge region. It is shown from the finite-element analysis that the ridge waveguide with a dimple is both low loss and fabrication tolerant.

Free-electron masers based on planar Bragg waveguides

A new scheme of the free-electron maser (FEM) with a ribbon electron beam is proposed in which the radiation is channeled in an open planar Bragg waveguide structure of two parallel plates with corrugated inner surfaces. The direction of corrugation is parallel to the radiation group velocity vector. The electron beam propagates in the waveguide at a large angle to its axis. The electron translation velocity is parallel to the direction of propagation of one of the partial waves that form the waveguide mode, which makes the maximum Doppler up-shift of the radiation frequency possible. A nonlinear analysis shows that the proposed FEM scheme provides a high gain (up to 30 dB). Using the Bragg waveguide, it is possible to ensure effective mode filtration, thus controlling the spatial structure of the output radiation.

Electric Field Distributions in the Open Cylindrical Silicon Carbide Waveguides

Progress in the build-up of high power microwave devices stimulates the intensive research of the open silicon carbide (SiC) semiconductor waveguides. SiC waveguides operating at the microwave range are presently being developed for advantageous use in high-temperature, high-power, and high-radiation conditions. We are going to present here results of electrodynamical analysis of the open cylindrical SiC waveguide. We have created a computer algorithm with 2D graphical visualization in the MATLAB language.

Asymmetrical waves in a helix and a system of helices forming an artificial medium

Propagation along a helix of asymmetrical waves excited at the open waveguide end with H 11 wave in the circular cross section is investigated. A system of helices forming a square array is considered. The effective dielectric constant of the array representing an artificial medium is determined. The calculated results are checked experimentally.

Pseudoinverse method for modal solutions of open dielectric waveguides

The vector finite-element method in the interior and the boundary integral equation of the exterior domain are investigated in order to analyze open dielectric waveguides. Boundary conditions are obtained by applying the continuity of the magnetic and electric fields at the surface of the waveguide. Since both the finite-element method and boundary integral equations have the final matrices of the form Ax=lambdaBx, the pseudoinverse method with a penalty factor is used. This new method provides the simultaneous solutions of propagating modes at the operating frequency, and it shows good agreement with previously published results for the analysis of the rectangular waveguide.

Uniform Ferrite-Loaded Open Waveguide Structure With CRLH Response and Its Application to a Novel Backfire-to-Endfire Leaky-Wave Antenna

A uniform ferrite-loaded open waveguide structure with composite right/left-handed (CRLH) response and its application to a novel backfire-to-endfire leaky-wave antenna are presented. The structure consists of a ferrite-filled rectangular waveguide open to free space at one of its small sides and biased perpendicularly to its large sides. Based on the fact that the leakage from the open side represents only a small perturbation in terms of guidance, an analytical dispersion relation for the approximately equivalent perfect magnetic conductor closed waveguide structure is derived. The unique dispersive properties of this structure, including its inherent CRLH balanced response (gapless nonzero group velocity transition between the left- and right-handed bands) and low-loss characteristics due to off-resonance operation, are extensively described, parametrically studied, and concretized by design guidelines. This theory is validated by both finite-element method and finite integration technique full-wave results and demonstrated experimentally. The leakage of the structure is exploited to build a full-space backfire-to-endfire scanning leaky-wave antenna, which is capable of both fixed-bias frequency scanning and fixed-frequency bias scanning, while being a perfectly uniform structure not requiring any chip tuning components. This feature, and its subsequent design simplicity, represents a fundamental advantage over previous CRLH metmaterial implementations. To the best of our knowledge, the proposed ferrite waveguide is the first and unique uniform structure exhibiting a CRLH response.

The layered element method in the dynamic theory of elasticity

A semi-analytical approach is proposed for the numerical analysis of the dynamic behaviour of elastic layered systems and waveguides with internal and surface nonuniformities. The approach is based on representing the reflected field in the form of an expansion in fundamental solutions for the layered structure as a whole. Unlike classical boundary elements, which represent the fundamental solutions for a homogeneous elastic space, layered elements identically satisfy the boundary conditions on all outer and inner plane-parallel boundaries. Hence, to find the unknown expansion coefficients it is necessary to satisfy boundary conditions only on obstacles, that assumes the use of many fewer elements than in the boundary element method, using which it is necessary to arrange them along all the outer and inner boundaries of the region considered. Moreover, each layered element exactly describes the wave structure of the solution, which is particularly convenient when solving problems of the transmission and reflection of travelling waves in open waveguides with obstacles. A brief description of an algorithm for constructing layered elements is given and examples of the use of the layered element method for solving two-dimensional and three-dimensional problems of diffraction in an open waveguide, and also for calculating the dynamic characteristics of bounded structural elements, made of laminated materials, are presented.

Diffraction by a Defect in an Open Waveguide: A Mathematical Analysis Based on a Modal Radiation Condition

We consider the scattering of a time-harmonic acoustic wave by a defect in a two-dimensional open waveguide. The scattered wave satisfies the Helmholtz equation in a perturbed layered half-plane. We introduce a modal radiation condition based on a generalized Fourier transform which diagonalizes the transverse contribution of the Helmholtz operator. The uniqueness of the solution is proved by an original technique which combines a property of the energy flux with an argument of analyticity with respect to the generalized Fourier variable. The existence is then deduced classically from Fredholm's alternative by reformulating the scattering problem as a Lippmann–Schwinger equation by means of the Green's function for the layered half-plane.

Guidance and Leakage Behavior of Uniaxial Ridge Waveguides

This paper addresses the guided-wave propagation in an open uniaxial ridge waveguide. The analysis is focused on the discrete modes, although including both guidance and leakage behavior. It is shown that, beyond a certain critical frequency, the surface guided modes may turn into leaky modes, due to the TE-TM mode coupling at the waveguide lateral boundaries. The numerical results were obtained using a conventional mode matching technique with a finite number of surface waves in each region. The results obtained for the guided modes are validated by comparison with those obtained through a more accurate analysis. The influence of the anisotropy and the geometrical parameters on the attenuation and phase constants of the leaky modes is shown.

Dual-Band Full-Space Scanning Leaky-Wave Antenna Based on Ferrite-Loaded Open Waveguide

A dual-band full-space scanning leaky-wave antenna based on a ferrite-loaded open waveguide structure is proposed. The lowest three bands of this structure are: the composite right/left-handed (CRLH) mode with positive group velocity first reported recently, the traditional isolator edge-guided mode, and a mixed forward/backward perturbed waveguide mode with a negative group velocity in its leaky-wave region. The leaky-wave regions of the CRLH and of perturbed waveguide modes are exploited to provide dual-band radiation. Due to their opposite group velocities, the two modes have their ports placed at both ends of the structure, which allows independent matching sections and also avoids the necessity of a diplexer. The antenna was demonstrated by both full-wave simulation and by experiment.

Open waveguide cavity using a negative index medium

An open waveguide cavity formed by a pair of planar waveguides, in which one guiding layer is a negative index medium and the other is a positive index medium, is theoretically demonstrated. For such a waveguide cavity the resonant frequency is independent of the total length of the waveguide system. With the coupled mode theory it is shown that energy flow circulation can be established through the special coupling between the waveguides at the resonant frequency, and thus the wave fields are localized. This phenomenon is further verified numerically with the finite-difference time-domain method. The quality factor of the open waveguide cavity is also discussed.

Simulation of wave processes in an open waveguide with diffraction-coupled radiation sources

Electrodynamic characteristics of an open waveguide formed by two diffraction gratings with distributed radiation sources have been studied by the method of experimental simulation. Such system was shown to give a good promise for creating hardware components and amplifiers operating in the millimeter wavelength range.