Circular Cylindrical Waveguide Research Articles

Conversion of the energy of a high-current REB into electromagnetic wave energy

Results are presented from a theoretical investigation and quantitative analysis of the physical processes that govern the efficiency of a coaxial device aimed at converting the energy of a relativistic electron beam into the energy of a TEM wave (a wave in a circular cylindrical coaxial waveguide). The key diffractional problem is solved exactly using a simplified theoretical model, which makes it possible to understand the mechanisms for the formation of a TEM wave and determine how the beam parameters and the design parameters of the converter affect the relative fractions of the kinetic energy of a relativistic electron beam and the energy of its own magnetic and electric fields that are transferred into the energy of the TEM wave field. The results obtained are analyzed quantitatively, and prospects for further theoretical and experimental research in this area are outlined.

Characterization of chiral materials at Ku-band using a circular cylindrical waveguide

The permittivity and the chiral admittance of a chiral material are determined from the measurements of field rotations obtained for the left and right circularly polarized waves and the guide wavelength in a section of Ku band circular cylindrical waveguide with an internal chiral coating. The results obtained from the automatic network analyser measurements in the frequency range 14.5–17.5 GHz demonstrate the usefulness of the proposed technique and results are presented for some commercially available chiral materials like 3 hydroxy butyrite- co -3 hydroxy valerate (PHB-PHV) and cellulose butyrate. Limitations of the proposed technique are also discussed.

Acoustic resonances in the presence of radial fins in circular cylindrical waveguides

This paper presents a method, based on matched eigenfunction expansions, for the determination of the frequencies of the acoustic resonances that can occur in a circular cylindrical waveguide in the presence of a number of thin radial fins of finite length in the axial direction. The fins are evenly distributed around the guide and we find that there are significant differences in the possible modes depending on whether the number of fins is even or odd and also that the qualitative behaviour of the mode frequencies changes when the number of fins passes a certain critical value. Simple approximate formulas are derived for the low-frequency modes under the assumption that the number of fins is large. The implications of our results are discussed for the case when the circular cross-section is replaced by an annular one, a situation of practical importance in the design of turbomachinery.

Analysis of a slot-coupled T-junction between circular-to-rectangular waveguide

This paper presents a rigorous analysis of a slot-coupled T-junction between a primary circular cylindrical waveguide and rectangular waveguide, forming the coupled T-arm. The analysis is based on moment-method formulation using full-wave basis functions and Galerkin's technique for testing. Expression for the coupling and reflection coefficients are found, taking into account the effect of finite wall thickness of the circular waveguide in which the coupling slot is milled. A comparison between the theoretical and experimental results on coupling and return loss are presented.

Plasma circular cylindrical waveguide in lossy material

The surface modes in the plasma circular cylindrical waveguide in a lossy material are analyzed, particularly for the variations of their propagation properties with plasma parameters and surrounding material. The characteristic equations of surface modes are derived, and their relevant approximate solutions are given. The limit results of this paper are consistent with that given in literature’s. The analysis show that it can be used to improve the properties of mode suppressors and fabricat cut-off attenuators.

ACOUSTIC SCATTERING BY A SPHERE IN A CIRCULAR CYLINDRICAL WAVEGUIDE

Multipole expansions are used to solve the problem of the acoustic scattering of an arbitrary mode in a circular cylindrical waveguide by a sphere situated on its axis. Both hard and soft boundary conditions for both the guide and the sphere are considered. The multipole method considered here, although only being appropriate to the above geometry, provides fairly simple equations from which accurate results can be obtained without much computational effort. These results, whilst being interesting in their own right, can be used as a check for more complicated numerical schemes that solve problems for arbitrary geometries. The multipole formulation also enables simple approximate formulae for the reflection and transmission coefficients to be obtained in the low-frequency and small-sphere limits. The same method, with a different set of multipoles, can be used to solve the problem of potential flow past a sphere in a circular tube, and this is done in an Appendix

Performance of a wideband, three-stage, mixed geometry gyrotwystron amplifier

A three-stage, mixed geometry gyrotwystron amplifier has recently been operated and characterized at 4.5 GHz. Gyrotwystrons are hybrids of the gyroklystron and gyro-traveling-wave tube (gyro-TWT) amplifiers. In the device which was studied, the first two stages were tunable rectangular resonator cavities, and the third (output) stage was a circular cylindrical waveguide traveling wave section. All three stages operate in fundamental mode, and are separated by cut-off drift regions. This experiment was conceived as an extension of a previous three-cavity gyroklystron experiment, the motivation being to improve upon the gyroklystron instantaneous bandwidth of 0.4% while not sacrificing efficiency or gain. Measurements of gyrotwystron performance showed a 1.5% instantaneous bandwidth, a fourfold increase over that of the gyroklystron. The gain-bandwidth product of the gyrotwystron exceeded that of the gyroklystron by a factor of 6. >

Acoustic radiation from two opposed semi-infinite coaxial cylindrical waveguides. II: separated ducts

The radiation of sound waves from two coaxial circular cylindrical waveguides is discussed in this article. Both ducts are semi-infinite in length, one extending from z = ℓ ‖ to z = -∞ and the other from z = 0 to z = +∞, where z is a coordinate measured along the cylinders' axis. Waves are incident from z = -∞ inside the smaller radius duct and the reflected, transmitted and radiated fields are calculated here for the case when the waveguides are separated by a gap of arbitrary length ℓ (ℓ < 0). In the first part of this study (Lawrie et al., Wave Motion 18, 121–142 (1993)) the model was solved for overlapping pipes ℓ > 0 by reducing the problem to a matrix Wieber-Hopf equation, which was solved by the introduction of an infinite constant vector satisfying a simple algebraic system of equations. This procedure does not follow through for the case of a gap, due to the presence of exponentially growing elements, and further analysis is required to solve for the Wiener-Hopf unknowns. Numerical results are presented here for a range of values of gap length and duct radii.

Cylindrical cavity-backed suspended stripline antenna-theory and experiment

The problem of a cylindrical cavity-backed suspended stripline (SSL) antenna is viewed as a transition of the SSL to a circular cylindrical waveguide opening into an infinite ground plane. The fields in the waveguide are expanded in terms of TE and TM modes. The effect of the radiating aperture on the modal expansion of the fields is taken into account by introducing reflection coefficients for each mode. The current on the SSL probe is assumed to have sinusoidal distribution. These simplifications reduce the original problem to that of a known radially oriented current residing on a dielectric sheet inside a circular-cylindrical cavity whose top wall has known impedances corresponding to different modes. The Green's function for this modified structure is found and is used to obtain a general expression for the input impedance. This expression is specialized to the case where the SSL probe and the radiating aperture are coupled through the dominant TE/sub 11/ mode only. This input impedance is translated to the measurement plane of the antenna. The computed and measured results are found to be in good agreement.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Trapped modes in a circular cylindrical acoustic waveguide

A hard cylindrical waveguide, filled with a uniform acoustic medium, has a circular cross section. A hard sphere is located with its centre on the axis of the cylinder. We look for a trapped mode, i. e. a mode of finite energy such that the normal velocity vanishes on both the sphere and the cylinder. The velocity potentials considered here have an angular variation exp (i α ) bout the axis of symmetry, where α is the azimuthal angle; it is well known that modes of this type cannot propagate to infinity if their wavenumber lies below a critical cut-off wavenumber. It is assumed that the radius of the sphere is sufficiently small and that the wavenumber lies just below the cut-off wavenumber; it is shown by an explicit construction that a trapped mode exists when there is a certain characteristic relation between the radius of the sphere and the wavenumber of the mode.

Computer-controlled system for surface resistance measurements of HT/sub c/ superconducting films

A measurement system capable of determining the microwave surface resistance of high-temperature superconducting films is described. The measurement is based on evaluating the resonant curve of a circular cylindrical waveguide transmission resonator. The cylindrical wall, and the top plane of the resonator are made of copper. The test sample is the ground plane of the resonator. The surface resistance of the test sample can be directly evaluated from the quality factor of the resonator when the surface resistance of copper is used as a reference. The computer-controlled measurement system consists of a backward-wave oscillator, the cylindrical resonator, a spectrum analyzer for the detection of power and frequency, and a refrigerator for cooling the resonator and the test sample. Several measurements have been made. Surface resistances of different thin-film samples have been determined. The lowest values measured so far approximate 25 m Omega at 66.8 GHz and 77 K. >

Radiation characteristics of a dielectric disk-loaded circular cylindrical waveguide

The radiation pattern of a circular cylindrical waveguide that is loaded inside with periodically spaced dielectric disks is derived by considering the region between two disks as a medium with anisotropic permittivity and using Schelkunoff's equivalence principle. The far-field electric field components and their relationship to cross-polarization ratio are determined. The variation of the latter quantity with the size, spacing, and dielectric constant of the dielectric disks is studied. >

Analysis of soft and hard strip-loaded horns using a circular cylindrical model

Strip-loaded horns with transverse (soft) and longitudinal (hard) strips are analyzed theoretically. The method is based on a circular cylindrical and uniform waveguide model with a periodic strip structure. The field is represented by an infinite series of space harmonics (Floquet modes) in the air-filled central region and in the dielectrically filled wall region. The tangential field is forced to be continuous across the air-dielectric boundary. The propagation constant and the total field (including the hybrid factor) can be determined by solving the resulting matrix equations. The convergence of the solution has been accelerated by calculating the higher-order terms analytically. It is shown that the soft-strip-loaded horn in principle exhibits the same electrical behavior as a corrugated horn. The horn represents an interesting alternative to the corrugated horn in wide-band or dual-band applications, in particular for millimeter waves and for lightweight applications onboard satellites. The hard-strip-loaded horn has potentially high gain and low cross polarization over a certain frequency range, dependent on the horn dimensions, thickness of the dielectric wall and on how strongly the stripline modes are being excited.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A K-space method of moments solution for the aperture electromagnetic fields of a circular cylindrical waveguide radiating into an anisotropic dielectric half-space

A method of moments solution is presented for the problem of determining the electromagnetic aperture fields that occur when a circular cylindrical waveguide radiates into an anisotropic dielectric-covered ground plane. The method of moments solution is derived by using a reaction matching technique and by using K-space theory to develop the aperture matrix elements of the system. An example of radiation into an anisotropic dielectric is given. The anisotropic dielectric for this example is assumed to be formed by the presence of a static magnetic field placed within a plasma.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Radiation characteristics of a corrugated circular cylindrical waveguide horn excited in the TE/sub 11/ mode

The design and experimental studies on a corrugated circular cyclindrical waveguide antenna that is feed-excited in the TE/sub 11/ mode with suppressed far-out sidelobes are reported. To reduce the spillover in the region 90 degrees >

Eigenvalues of propagating waves in a circular waveguide with an impedance wall

The paper determines the eigenvalues and conditions of propagation of hybrid modes inside a circular cylindrical waveguide with an impedance wall. The analysis allows for different longitudinal and transverse impedances on the walls. A general characteristic equation is derived from which the corresponding characteristic equations for circular cylindrical waveguides with a perfectly conducting wall, a corrugated wall or a dielectric lined wall can be obtained. Finally, it is found that the propagation of hybrid modes in circular waveguides with large radii is independent of the surface impedance.

Multiple scattering of EM waves by dielectric spheres located in the near field of a source of radiation

An analysis of multiple scattering of electromagnetic (EM) waves by two loss-free dielectric spheres with radii greater than a wavelength and located in the bear field of a source of radiation is presented. The incident field is expressed in terms of spherical vector wave functions (SVWF). Translational and rotational addition theorems are employed to express the SVWF of the incident field in the coordinate system associated with the dielectric scatterer. Numerical computations are performed for obtaining the amplitude and phase patterns of fields multiply scattered by two loss-free dielectric spheres, whose centers are located on the boresight axis and in the nearfield of an open-ended circular cylindrical waveguide excited in its dominant mode. Numerically computed results show good agreement with measured results obtained from a systematic experimental study on forward scatter performed in the X -band.

Coaxial waveguide to circular cylindrical waveguide junction

The abrupt junction between a coaxial waveguide with hollow inner and a cylindrical waveguide has previously been analysed using a moment method for the case where the hollow inner has an infinitesimally thin wall. The paper describes modifications which permit a wall of finite thickness to be accommodated.

Electromagnetic effects in an elastic circular cylindrical waveguide

The problem of wave propagation in an elastic, thin circular cylindrical tube, including the possibility of propagation of rotating waves, is examined with the use of a nonlinear electromagnetic membrane theory. Some related special cases, which include wave propagation in a class of magnetic polarized rigid tubes and rigid plates, are also briefly discussed.

On a Measurement Method of the Tensor Permeability of Ferrite Using Faraday Rotation

A new measuring technique of the tensor permeability of ferrite in the microwave frequencies based on Faraday rotation is proposed. A circular cylindrical waveguide containing a longitudinally magnetized ferrite rod is used. A plane polarized TE11 wave is incident upon the section where the ferrite cylinder is placed. One end of the circular waveguide is short-circuited by a movable short-circuit plunger, which holds the ferrite cylinder through a hole drilled at the center. The angle of Faraday rotation and the position of the minimum voltage point of the elliptically polarized standing wave are measured far from the ferrite section. In addition to the measurement theory, several discussions are given: i) the relationship between a diameter of the specimen and the cutoff wavelengths of modes in the waveguide, ii) the extent of unwanted reflections due to the impedance mismatch at the end of the rod. As an experimental example, the tensor permeabilities of a polycrystalline rod of YIG are measured at the frequency 3.75 GHz with some dc magnetic field intensities.