Section Of Rectangular Waveguide Research Articles

Coaxial‐to‐circular waveguide transition with broadband mode‐free operation

A simple transition between a circular waveguide and a coaxial cable having mode-free operation over more than an octave bandwidth is presented. The transition consists of a conical coaxial probe, a rectangular waveguide section and a linearly tapered transformer from the rectangular to circular waveguide. The transition shows a reflection coefficient of < –20 dB, a transmission coefficient of >–0.57 dB and a higher-order mode level of < −25 dB over a frequency range 1.04–2.53 times the TE11 mode cutoff frequency.

Nonspecular reflection of Gaussian wave beams on a two-dimensional periodic array with shorted waveguides of rectangular cross-section

This paper investigates nonspecular reflection of three-dimensional Gaussian wave beams from a two-dimensional periodic grating of short-circuited rectangular waveguides. ‘Orthogonal’ beam reflection from a periodic structure has been examined. The correlation of reflection rates in terms of power and the length of short-circuited waveguides has been estimated for specular and nonspecular beams. The relation of the reflected beams’ directional pattern in the far field to the array and incident beam parameters has been investigated. The splitting effect of the reflected beams’ directional pattern has been established in the case of p-polarized beam incidence. The possibility of applying a grid of rectangular waveguide sections in an electromagnetic field impulse compressor has been demonstrated. Various operational modes of the reflection grating used as a coupling element between the open-structure resonator and the transmission line have been described. The effects of directional pattern reduction and reflected beam directional pattern deformation have been established. These effects have been physically grounded. The results are presented in the form of three-dimensional directional patterns of the diffuse beam field in the far field. The calculation algorithm is based on the available solutions of the key vector problems of plane linearly polarized electromagnetic wave diffraction on two-dimensionally periodic structures.

TECHNIQUE FOR INHOMOGENEOUS PROFILES IN THE CROSS-SECTION OF THE HELICAL RECTANGULAR WAVEGUIDE

This paper presents the technique to solve inhomogeneous profiles in the cross section of the helical rectangular waveguide. We present the technique to solve inhomogeneous dielectric profiles and the relation to the method of the propagation of electromagnetic fields along a helical waveguide with a rectangular cross section. The inhomogeneous examples will introduce for a dielectric slab, for a rectangular dielectric profile, and for a circular dielectric profile, in a rectangular metallic waveguide, in the cross section of the helical waveguide. This model is useful to improve the output results of the output power transmission in the cases of space helical waveguides, by increasing the step’s angle or the radius of the cylinder. The application is useful for space helical waveguides in the microwave and the millimeter-wave regimes.

Measurement of Complex Permittivity of Cylindrical Objects in the E-Plane of a Rectangular Waveguide

Remote sensing of dielectric properties is used for numerous applications such as the field evaluation of soil water, salinity, or the organic matter content. The objective of this study is to measure dielectric properties of cylindrical shaped samples for the previously specified applications. The proposed method employs an analytical approach for determining the complex permittivity of cylindrical dielectric objects placed in the E-plane of a rectangular waveguide. The overall procedure is based on the measurement of reflection and transmission coefficients of the test specimen by placing it inside a section of rectangular waveguide. The reconstruction of dielectric properties of the test sample from the measured scattering coefficients is carried out using the newly proposed closed-form expressions, which are derived by transforming the actual circular cross section of the cylindrical sample into the equivalent multilayered rectangular cross sections. The dielectric properties of a number of specimens, including typical plastics and vegetation samples, are determined using the proposed approach. The typical error in the reconstruction of the dielectric constant of these samples having moderate permittivity values is found to be less than 5%.

WAVE PROPAGATION IN A WAVEGUIDE SECTION WITH SHARP CORRUGATIONS

The rigorous excitation equations are used to analyze wave propagation in a rectangular waveguide section with sharp periodic corrugations whose height is much greater than the period. It has been shown that the Brillouin diagram of the corrugated and regular waveguides in the case of strong gradient scattering is characterized by qualitatively the same frequency dependence of the longitudinal wavenumber. The only difference is that the cutoff frequencies of the corrugated waveguide modes increase with decreasing the corrugation period, and it is always possible to implement the single-mode regime within an arbitrary frequency range lying higher than the first cutoff frequency. The effect can be used to suppress the mode competition in microwave amplifiers, as well as in narrow-band oscillators provided that the latter involve the Bragg reflectors as a feed-back.

A Closed-Form Formula for Dispersion Characteristics of Fundamental SIW Mode

An accurate closed-form formula is derived from an analytical method to calculate dispersion properties of the substrate integrated waveguide (SIW). The derived equation which is a function of geometrical parameters is used to accurately estimate the cutoff frequency of the dominant mode at a low leakage condition. The unit cell of an SIW can be considered as two consecutive rectangular waveguide sections with the specific difference in their widths. The propagation constant is extracted by applying the Floquet theorem to the overall transmission matrix of the single unit cell. The proposed formula agrees well with numerical solutions as well as reported empirical equations in a wide range of structure parameters.

Calculation of coherent synchrotron radiation in toroidal waveguides by paraxial wave equation

A new technique for the simulation of coherent synchrotron radiation (CSR) and space-charge fields from a single electron bunch in straight or toroidal rectangular waveguide sections has been developed. It is based on the integration of the paraxial approximation to the wave equations, using the perturbation technique where the bending radius is large compared to the dimension of the waveguide. We have implemented an unconditionally stable integration method in the time domain with transparent boundary conditions that allows the use of a minimally sized computational domain about the bunch. This technique explicitly enforces the causality condition so that no portion of the fields can propagate faster than the speed of light, can be used with arbitrary three-dimensional charge distributions, and contains corrections for finite energy. We have also developed a method for the calculation of the transverse forces within the bunch including space-charge. This method has been developed for incorporation with a particle-in-cell code so that we may self-consistently model CSR and space-charge in combinations of bending sections with a fully dynamic electron bunch in an efficient manner. In this paper we describe the model and methods for calculation of the fields in detail and compare results to theory wherever possible.

Radiation Characteristics of Two-Element Phased Array Using Rectangular Waveguide Sections with a Surface Wave Excitation

Radiation Characteristics of Two-Element Phased Array Using Rectangular Waveguide Sections with a Surface Wave Excitation

Radar Cross Section Modeling and Measurements of Inlets and Cylinders With Skew Blades

Ray based methods give useful scattered field predictions from the skin of the aircraft illuminated by an incident plane wave. They can also be used to predict the returns from simple inlets and cavities but fail when complex terminations such as skewed blades are encountered. As a possible enhancement to the ray-tracing procedure, an auxiliary program based on the modal method was developed to predict the scattering of electrically large and complex jet inlets with engines. For the present development, it is assumed here that these structures can be approximated by a series of rectangular, circular, coaxial and sectoral waveguide sections. The field matching technique is used to give the generalized scattering matrices of the junctions between these waveguide sections. By combining the scattering matrices of the waveguide sections representing the inlet and engine, an overall S-matrix is obtained. Knowing the modes induced at the inlet aperture by the incident plane wave, the scattered fields from the inlet and engine can be readily predicted in all directions. Monostatic RCS measurements of a 0.706 m diameter test cylinder containing 30 skewed blades mounted on a center shaft with a conical hub have been performed at X-band. The dimensions of the structure, the number and orientation of the blades are consistent with those of existing jet engines. Fair to good agreement between predictions and measurements verify the developed software and analytical method used

Propagation of the H 10 mode in a rectangular waveguide with a dielectric discontinuity

The transmission of the H10 wave through a waveguide-capillary cavity in the form of a section of a rectangular waveguide with a square liquid-filled capillary inside is studied theoretically. The capillary passes through the center of the waveguide perpendicularly to its wide walls. The problem is solved by constructing the mirror images of the capillary on the narrow walls of the waveguide with subsequent consideration of the diffraction of the Brillouin components of the H10 waveguide mode by a periodic “array of capillaries.” It is shown that a resonance minimum in the frequency dependence of the energy coefficient of transmission of the H10 wave through the waveguide-capillary cavity can be explained by the destructive interference of diffraction harmonics propagating in antiphase. The experimentally found existence of the capillary optimum dimension at which the resonance minimum is the most pronounced is corroborated analytically.

Characterization of rectangular waveguide with a pseudochiral /spl Omega/ slab

A mode matching approach has been employed for evaluating the matrix S of the section of rectangular waveguide with pseudochiral /spl Omega/ slab. Scattering characteristics for different localizations of the /spl Omega/ slab in the guide are predicted numerically and verified by measurements. Based on the numerical analysis, the scattering properties of the guides are discussed. Scattering parameters are next applied in an optimization procedure to extract constitutive parameters of the /spl Omega/ slab used in experiment.

Novel TE/sub 10δ/ rectangular-waveguide-type resonators and their bandpass filter applications

New dielectric-filled rectangular-waveguide-type TE/sub 10/spl delta// resonators are presented. A dielectric-filled rectangular waveguide section (WGS) has inductive impedance at the open-end faces. Using this property and the frequency dependency of the wave impedance of the WGS, we calculated the resonant frequency and the slope parameter of the waveguide-type resonators. The resonant frequency depends strongly on the width of the WGS and loosely on the height and the length. The calculated resonant frequencies agree well with measured data. One of the proposed bandpass filters shows highly reduced spurious up to three times the center frequency. Quality factors of the resonator and effects of a housing are also discussed.

Thickness-independent measurement of the permittivity ofthin samples in the X band

A method is proposed for measuring the complexpermittivity of thin materials. The method allows us tosimultaneously measure the permittivity and thickness of thematerial, allowing us in particular to obtain ameaningful estimate of the average thickness of naturalmaterials. The measuring system consists of a section ofrectangular waveguide, operating in the X band and modified toaccommodate the material under measurement, and two standardimpedance loadings (short-circuit and matched load). Tworeflection coefficient values, measured by a vector networkanalyser at the input of the waveguide sample-holder, allow thedetermination of the parameters of interest by means of anumerical procedure employing a genetic algorithm. The methodhas been tested on certified dielectric materials andpreliminary results are presented concerning paper and thincardboard.

A millimeter-wave six-port reflectometer based on the sampled-transmission line architecture

This letter presents a proof-of-concept implementation of a millimeter-wave reflectometer for measuring complex reflection coefficients. The reflectometer is based on the six-port architecture and consists of a single section of WR-10 rectangular waveguide and a set of three Schottky power detectors. Design considerations as well as measurements in the 75 to 110 GHz range are described and discussed. Because of its simple architecture, the reflectometer is amenable to scaling for measurements well into the submillimeter-wave region of the spectrum.

CAD of evanescent-mode bandpass filters based on the short ridged waveguide sections

The paper presents the internal details of a developed full-wave algorithm for the computer-aided design of evanescent-mode bandpass filters formed by single- or double-short ridged waveguide sections. New filter configurations with an enlarged cross section of filter housing and nonconventional notch-strip-notch elements providing improved stopband performance are given special considerations. Additional input–output transformers built on rectangular waveguide sections are used in designing broadband filters. Characteristics of one of the designed filters are verified by measured data. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 354–365, 2001

Synthesis of configuration of uniformly radiating longitudinal slots in the sections of nonregular rectangular waveguides

The integral-equation method has been applied along with perturbation theory to investigate the leaky-wave parameters of the fundamental mode in the regular waveguide with a narrow longitudinal slot on its broad wall, opened into shielded semispace. Then, the simple analytical formulas have been derived for the engineering synthesis of radiating elements (REs), which are formed by a nonuniform waveguide section with a nonregular slot on its broad wall. The long slot was cut in the longitudinal direction along certain curved or several connected broken lines, forming small local angles with the waveguide axis. The synthesis of RE's by single-mode approximation has been carried out for the condition of good uniformity of radiating electrical-field distribution along the RE axis near the slot. Good agreement of theoretical and experimental results was obtained.

Design of compact waveguide twists

A new geometry for compact twist components composed of rectangular and circular waveguide sections is presented. The proposed twist geometry presents several advantages: 1) It can be designed for any rotation angle; 2) it is extremely short and, therefore, well suited for satellite communication applications; 3) its electrical behaviour is excellent for either narrow or broad frequency bands; and 4) a very accurate and efficient full-wave mode-matching method can be used to analyze these twists. A software package has been developed to design the proposed compact twist structure in a full-wave method.

Dual-mode dielectric or air-filled rectangular waveguide filters

An accurate design technique of dual-mode microwave dielectric or air-filled rectangular waveguide filters is described. Dual-mode coupling is realized by a section of rectangular waveguide with square-corner-cut. The unequal couplings between dual-mode pairs of the cavities is provided by a section of evanescent mode waveguide. Rigorous analyses are applied to characterize the microwave junctions and to obtain the design parameters for the filter. The design procedure used to determine the dimensions of the waveguide junctions with a minimum of computational effort is described. The design is demonstrated by four-pole and six-pole dual-mode rectangular waveguide elliptic function filters. Excellent agreement between computer simulation and experimental results with absolutely no tuning justifies the design.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electromagnetic-wave absorption in highly collisional plasmas

An experimental and theoretical investigation of basic plasma-physics processes relating to the absorption of electromagnetic waves in collisional plasmas is described. One-way absorption of 63 dB at 4 GHz was demonstrated in a section of plasma-loaded rectangular C-band waveguide. The ultraviolet photoionization plasma-production technique employed permits independent variation of the plasma-density profile and electron-collision frequency. A theoretical model for the absorption and scattering processes, which includes scattering contributions from the plasma-vacuum interface, and partial reflections and collisional absorption in the bulk plasma, is in reasonable agreement with the experimental results.

Field theoretical computer-aided design of rectangular and circular iris coupled rectangular or circular waveguide cavity filters

The rigorous CAD of a class of rectangular and circular waveguide cavity filters which are coupled by rectangular and/or circular irises is described. The design theory is based on the full-wave mode-matching method for three key building block elements (asymmetric rectangular double-step, asymmetric rectangular-to-circular and circular-to-circular waveguide junctions) associated with the generalized S-matrix technique for composite structures. The waveguide filters may be arbitrarily composed of the key building block elements and the rectangular or circular waveguide sections between them. Finite iris thicknesses, higher-order mode interactions, and asymmetric structures are rigorously taken into account. The theory is verified by measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>