Parallel Plane Waveguide Research Articles

Ray Optics-A Novel Approach to Scattering by Discontinuities in a Waveguide

Waveguide discontinuities are analyzed conventionally by techniques utilizing the induced field in the vicinity of the discontinuity for calculation of the distant reflected and transmitted field in the various modes. Evaluation of the induced field constitutes the major difficulty in the problem. By an alternative and novel approach explored in this paper, scattering by a discontinuity in a waveguide is deduced from a knowledge of its far zone (asymptotic) scattering properties in free space. In contrast to "small obstacle" techniques wherein similar concepts are utilized for isolated scatterers whose size is small compared to the free-space wavelength, the present procedure accommodates also large discontinuities such as strips, apertures, bifurcations, changes in cross section, etc. The description of various scattering processes is carried out naturally in terms of ray optics which provides at each stage of the calculation an interpretation of the associated physical mechanism. The procedure is illustrated for apertures, strips, and bifurcations in a parallel plane waveguide for which comparisons with exact solutions can be made. It is found that while the ray-optical technique is best suited to the high-frequency (multimode) regime far from modal cutoffs, it is capable of providing remarkable accuracy even in the range of propagation of only the dominant mode.

Ray Theory of Reflection from the Open End of a Waveguide

Ray methods have been widely used to calculate high frequency scattering by objects in an unbounded medium, but they have not been used much for waveguide problems. To show that they can be used for waveguides, we treat by ray methods reflection from an open-ended parallel plane waveguide propagating several modes. The incident mode is decomposed into two plane waves whose scattering by the edges at the termination produces the reflected field. The singly diffracted cylindrical wave originating at each. edge, which is known from the asymptotic theory of diffraction by a single wedge, is represented by means of diffracted rays. Then the stem of the fields on the multiply reflected rays is converted into modal form. This yields formulas for the reflection coefficients in the various modes due to single diffraction. In addition double and multiple diffraction are also taken into account, yielding improved formulas for the reflection coefficients. The results of extensive numerical calculations for $TE$ and $TM$ modes incident in flanged and unflanged open-ended waveguides are presented, and are compared with calculations based on exact solutions when these are available. It is found that the single diffraction results account for the average behavior of the amplitude and phase of the reflection coefficients. The inclusion of multiple diffraction accounts for the finer details and yields excellent accuracy even for wave guide height-to-wavelength ratios as small as $1/3$ in the TM case. These results suggest that the ray method also provides an accurate means for analyzing other types of waveguide discontinuities.

Ray-optical techniques for waveguide discontinuities

Abstract : Ray methods are employed in connection with scattering by discontinuities in waveguides is analyzed in the work reported here. Since the notion of a ray is generally associated with the local propagating plane wave fields encountered at high frequencies, it is to be expected that ray solutions apply only when the wavelength is small compared with critical dimensions of a guiding or scattering structure. However, it is shown that even the low frequency regime can be accommodated with good accuracy, thereby making the ray-optical techniques a powerful tool for the study of waveguide scattering problems. To render a ray-method analysis useful, it is necessary to convert these fields into a sum of waveguide modes whose amplitudes furnish the modal reflection, transmission and coupling coefficients. This conversion can be accomplished systematically in parallel plane and circular regions. Reflection from the open ends of parallel plane waveguide is analyzed in detail. In the unflanged case, the ray results agree remarkably well with the exact solutions even for wavelengths as long as six times the width of the guide. Data are also presented for flanged terminations for which no exact solution is available. (Author)

Propagation of the Quasi-TEM Mode in Ferrite-Filled Coaxial Line

The Suhl and Walker approximation for the propagation constant of the quasi-TEM mode in ferrite-filled parallel plane waveguide has been applied to the ferrite-filled coaxial line. The approximation is compared to exact solutions for a coaxial line filled with a lossless ferrite with close agreement. The propagation constant of the quasi-TEM mode is determined by measuring the complex reflection coefficient of a plane ferrite-air interface. The /spl alpha/ and (/spl beta/ are compared to the Suhl and Walker approximation with losses, and qualitative agreement is found. In order to relate the measured values to the propagation constants, the boundary value problem of the reflection from a plane ferrite-air interface is investigated. Expressions are derived which relate the real and imaginary parts of the propagation constant in the ferrite to an approximation to the complex reflection coefficient of the TEM mode in the empty line.

Radiation from some periodic structures excited by a waveguide

In this letter the problems of radiation from a set of semi-infinite parallel plates and of radiation from uniform and modulated corrugated surfaces excited by a parallel-plane waveguide are solved exactly. To the authors' knowledge, the latter two configurations have not been previously considered in the presence of sources.

Scattering by a semi-infinite impedance strip in a waveguide

The problem of dominant mode scattering by a symmetrically placed impedance strip in a parallel plane waveguide is solved exactly. The mode matching technique used is considerably more straightforward than the Weiner-Hopf method and is applicable to a number of other problems.

The Radiation Properties of a Parallel-Plane Waveguide in a Transversely Magnetized, Homogeneous Plasma

The Wiener-Hopf technique is used to study the radiation from a parallel-plane waveguide embedded in a homogeneous anisotropic plasma in which the external magnetic field is perpendicular to the direction of propagation and parallel to the perfectly conducting planes of the guide. The incident field in the guide is a TEM wave, which propagates in the positive z direction. The parallel-plane guide terminates at z = 0, causing a reflected field in the waveguide, a radiation field, and a surface wave that is guided along the outer surface of one of the perfect conductors. Expressions are found for these field components, and the results are discussed for the different frequency ranges.

Propagation of the Quasi-TEM Mode in Ferrite-Filled Coaxial Line

The Suhl and Walker approximation for the propagation constant of the quasi-TEM mode in ferrite-filled parallel plane waveguide has been applied to the ferrite-filled coaxial line. The approximation is compared to exact solutions for a coaxial line filled with a lossless ferrite with close agreement. The propagation constant of the quasi-TEM mode is determined by measuring the complex reflection coefficient of a plane ferrite-air interface. The /spl alpha/ and (/spl beta/ are compared to the Suhl and Walker approximation with losses, and qualitative agreement is found. In order to relate the measured values to the propagation constants, the boundary value problem of the reflection from a plane ferrite-air interface is investigated. Expressions are derived which relate the real and imaginary parts of the propagation constant in the ferrite to an approximation to the complex reflection coefficient of the TEM mode in the empty line.

TE Mode Excitation on Dielectric Loaded Parallel Plane and Trough Waveguides

A theoretical and experimental study of the launching of TE surface wave modes on dielectric loaded parallel plane and trough waveguides has been performed. The source is a linear transverse current filament perpendicular to and extending across the space between the parallel side walls. Families of curves are presented, which show the bidirectional Iaunchlng efficiencies for the dominant TE modes of these two transmission lines as a function of dielectric constant, dielectric slab thickness, and current filament location. Measured bidirectional efficiencies are compared to the theoretically predicted values. Measured unidirectional launching efficiencies as high as 97 per cent were obtained for the case where a short circuit is located on one side of the current filament.

Propagation in a Dielectric-Loaded Parallel Plane Waveguide

A theoretical analysis of wave propagation in a parallel plane waveguide partially filled with a dielectric is performed. This transmission line is a symmetrical three-region structure consisting of two infinite parallel conducting planes with a dielectric slab of rectangular cross section between and contacting each of the planes. It has been found that TEM and TM modes cannot propagate on this structure. This investigation is concerned with TE modes, although hybrid modes can also propagate on this line. The lowest order TE mode, which is the dominant mode, has no cutoff and hence is inherently suited to extremely wide bandwidth operation. Equations have been presented for the field components, guide wavelength, cutoff criteria, power handling capabilities, wall losses, and dielectric losses as a function of the operating wavelength, waveguide dimensions, and material constants. In the case of the dominant mode, design curves covering a large range of wavelengths, dimensions, and dielectric constants are presented. For a loosely bound wave, the losses are comparable or less than those of conventional rectangular waveguide and the power handling capacity is an order of magnitude greater.

Propagation in Ferrite-Filled Microstrip

The propagation constant of a ferrite-filled microstrip is measured as a function of the longitudinal static magnetic field, The results agree with the analysis by Van Trier of the infinite parallel plane waveguide filled with gyromagnetic media. The analysis is extended to anisotropies greater than 0.5. A simple relationship between propagation constant and anisotropy for the quasi-TEM mode with small spacing (X<<lambda/sub g/) is noted. Cutoff spacings for higher modes are calculated. An apparatus for the measurement of propagation constant independently of interface reflections is described.

Wave-guide interpretation of atmospheric waveforms

The precise current variation in the lightning discharge channel and the propagation characteristics of the transmission path for the low-frequency radio waves generated, provide possible explanations of the finer details of recorded electric-field change waveforms and some of the observed anomalies in the application of the pulse-reflection theory to “atmospherics.” A graphical construction for the prediction of waveforms, given the source conditions, indicates how the change in shape with reflection order of the ionosphere-reflected pulses can be explained in terms of source effects and the mode responses of an imperfectly conducting infinite parallel-plane wave-guide, whose known propagation characteristics give a qualitative explanation of the diversity of waveforms recorded. The dependence upon range and time of day provides experimental confirmation of Budden's wave-guide approach. One type of waveform, observed during day and night, indicates a directional variation of the propagation factor transcending the diurnal variation over a certain region.