An Analytical Design and Analysis Method for a High-Power Circular to Rectangular Waveguide Mode Converter and Its Applications

An analysis of hybrid modes in a rectangular waveguide filled with chiral material is presented in this paper. The modal wavenumbers are computed using the finite difference method together with Muller's root-finding algorithm. A novel scheme is presented whereby the validity of the numerical solution is established with analytical results. Using this numerical methodology, the existence of complex modes for a rectangular chiral waveguide is confirmed. Other notable features such as mode bifurcation and low frequency effects of chirality are also discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

To accurately measure the performance of dielectric loaded circuits for gyrotron traveling wave tubes, a novel topological structure to generate the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sup> or TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sup> (superscript represents circular waveguide) mode is proposed and verified in this paper. The topology is constituted by an overmoded TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">□</sup> to TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">□</sup> (superscript represents rectangular waveguide) mode converter with multiple matching steps and a taper from TE20 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">□</sup> to TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sup> or TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sup> mode. This topology allows the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sup> or TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sup> mode to be excited by changing the taper dimensions. Simulation results reveal that the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sup> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sup> mode converters, respectively, have a 1-dB bandwidth of 12.8 and 9.3 GHz with an excellent performance. Converters for the back-to-back millimeter-wave measurements were fabricated with computerized numerical control and wire cutting techniques. Vector network analyzer measurements are in good agreement with the simulations.

In recent years, R&D for pulse compression and power distribution systems for the Next Linear Collider has led to the invention of many novel rf components, some of which must handle up to 600 MW of pulsed power at X‐band. These include passive waveguide components, active switch designs, and non‐reciprocal devices. Among the former is a class of multi‐moded, highly efficient rf components based on planar geometries with overmoded rectangular ports. Multi‐moding allows us, by means of input phasing, to direct power to different locations through the same waveguide. Planar symmetry allows the height to be increased to improve power handling capacity. Features that invite breakdown, such as coupling slots, irises and H‐plane septa, are avoided. This class includes hybrids, directional couplers, an eight‐port superhybrid/dual‐mode launcher, a mode‐selective extractor, mode‐preserving bends, a rectangular mode converter, and mode‐mixers. We are able to utilize such rectangular waveguide components in systems incorporating low‐loss, circular waveguide delay lines by means of specially designed tapers that efficiently transform multiple rectangular waveguide modes into their corresponding circular waveguide modes, specifically TE10 and TE20 into circular TE11 and TE01. These extremely compact tapers can replace well‐known mode converters such as the Marié type. Another component, a reflective TE01‐TE02 mode converter in circular waveguide, allows us to double the delay in reflective or resonant delay lines. Ideas for multi‐megawatt active components, such as switches, have also been pursued. Power‐handling capacity for these is increased by making them also highly overmoded. We present a design methodology for active rf magnetic components which are suitable for pulse compression systems of future X‐band linear colliders. We also present an active switch based on a PIN diode array. This component comprises an array of active elements arranged so that the electric fields are reduced and the power handling capability is increased. Novel designs allow these components to operate in the low‐loss circular waveguide TE01 mode. We describe the switching elements and circuits.

A compact mode converter that transforms TM01 circular waveguide mode to TE10 rectangular waveguide mode is investigated. It consists of a circular waveguide with a short circuit terminal and a rectangular waveguide which is perpendicular to the circular waveguide. Simulation results show that conversion efficiency of the mode converter is about 99.8% at central frequency of 1.75 GHz, and the total return loss is approximately -30 dB. The experimental results are well consistent with the computer simulation, which demonstrates the feasibility and high power handling capacity of the mode converter.

The field distributions of various modes in rectangular waveguides filled with uniaxial media are presented. The presented cases include aligned cases when the optic axis is parallel to one of the coordinate axes and the tilted cases when the optic axis is not parallel to any of the coordinate axes but still lies within one of the two side-wall planes. In the aligned uniaxial-z case the analytical solution is compared with the results of the dyadic green's functions (DGF). In other aligned cases the field distributions of selected extra-ordinary wave modes are also plotted and to be compared with the isotropic case. In the tilted cases, the field distributions of the hybrid modes which are coupled ordinary-waves and extra-ordinary waves show asymmetry which is not seen in the aligned cases and isotropic case. The validity of the hybrid mode field plots are verified by comparing a limiting tilted case with analytical solutions of an aligned case.

Small circular waveguide mode converters used in the 28 GHz, 200 kW ECH system for the Hitachi tokamak HT-1 have been developed. In order to convert from the TE02 to the TE11 mode, TE0202-to-TE01 and TE01-to-TE11 mode converters are used. Both converters use periodic waveguide wall perturbations, the case of the former, circularly symmetric perturbations, and in the case of the latter, curvature perturbations. The lengths of the mode converters were successfully shortened with high mode conversion efficiencies by decreasing the number of periods and then optimizing the periods using quite a small diameter for the converters. The 30ϕ TE02-to-TE01 mode converter is 103 · 34 mm long and its mode conversion efficiency measured by a scalar network analyser is 96% at 28GHz. The TE01-to-TE11 mode converter is 427 · 38 mm long and has an efficiency of 79%, which is 10% lower than the design value. This discrepancy resulted mainly from mode conversion from the TE11 to the TE12 mode, caused by the smaller number of...

We designed a compact broadband mode converter based on metasurface technology, operating in the 180-210GHz band (the effective bandwidth is approximately 22GHz), which achieves high-efficiency conversion from the TE10 mode in a standard WR-4 rectangular waveguide to the TE01 mode in a circular waveguide. The mode converter consists of two sub-mode converters: the first, based on a magic-T waveguide, transforms the TE10 mode into the TE20 mode, and the second, based on a metasurface, converts the TE20 mode into the TE01 mode. Simulation results demonstrate that the conversion efficiency from the TE10 mode to the TE01 mode reaches a maximum of 88.3% (184.6GHz), with a return loss 8.4%. This metasurface-based mode converter can replace traditional complex transitional waveguide structures, providing a solution for generating high-quality TE01 mode in the terahertz band. Furthermore, the theoretical approach can be extended to the generation of other modes in the terahertz band.

This paper presents the design of a unique multimode extractor and converter of higher order modes of a circular waveguide. The multi-mode extractor couples first five circular waveguide propagation modes TE11, orthogonal TE11(o), TM01, TE21, and TE21(o) that includes the three tracking signals (i.e. sum signal, elevation signal, and azimuth signal) used in a high-frequency monopulse tracking system and two communication channels for transmitting and receiving signal at Ka band. This design is based on amplitude and phase characteristics of the higher-order modes TM01, TE21, and TE21(o) excited in circular waveguide. TE21 and TE21 (o) modes are extracted from circular waveguide to TE10 mode in rectangular waveguide by two longitudinal slots milled in the circular waveguide. TE11 mode is coupled using two coupling slots and H-plane power combiner. A turnstile junction is used to extract TM01 and TE11(o) mode. This multimode tracking system is designed both for linear or circular polarized ground earth station antennas to track orbiting satellites.

The risk of sand production must be evaluated from very early stages of field development planning to select the optimum well completion, and if required, identify the appropriate sand control options. However, during the appraisal or early development stages, sand production predictions often cannot be verified against field data because the lack of sanding observations. The analysis of predicting the onset and severity of sand production generally consists of using analytical or numerical rock mechanical models and ideally calibration with field sand production data. In this paper we show how in the absence of field sanding data, reliable sanding predictions can still be achieved by combining commonly used analytical and numerical prediction methods. This approach has been validated using a brown field dataset from South East Asia with several sand producing wells and multiple pressure depleted reservoirs. The analytical method uses a poro-elastic model and core-calibrated log-derived rock strength profiles with an empirical effective rock strength factor (ESF). The ESF should be calibrated against documented field sanding observations from wells with credible formation and drawdown pressures. The numerical method uses a poro-elasto-plastic model defined from triaxial core tests. The rock failure criterion in the numerical method is based on a critical strain limit (CSL) corresponding to the failure of the inner wall of thick-walled cylinder core tests or if existing field sanding data. In the brown oil field example, both analytical and numerical methods accurately predict the onset of sanding in the sand-prone wells. The core-based CSL defined by the numerical method match very well with the field sanding data with a very small margin of error. In contrast, the default and non-calibrated ESF values commonly used in the analytical method required considerable tuning to match with the field sanding data. This suggests that the core-based CSL can be used with a reasonable confidence for sand production prediction purposes in the field and the prediction can be as reliable as field-calibrated models. After the field validation, the predictions for planned infill wells by both analytical and numerical methods were consistent and similar. The paper will show how this approach is used in two other fields from the Asia Pacific region both at appraisal stages and with no field sanding data. Both cases show that different ESF values are required to match with the numerical simulations. In the absence of field sanding observation, particularly in the early stages of field development, the use of non-calibrated default ESF values in the analytical method could lead to erroneous sanding assessment and poor sand management decisions. Application of a combined analytical and numerical sanding evaluation enhances the reliability of sand production predictions. After a calibration is obtained, either with field sanding data or calibration against numerical simulation and core-based CSL criteria, the analytical method can be used with confidence and has the added benefits of simplicity and quick realizations of various scenarios and output plotting capabilities and inputs for sand control and well completion decisions.

Marcatili’s analytical solution for the guided modes of rectangular optical waveguides (ROWGs) depends on (1) using the separation of variables (SOV) and (2) applying the paraxial approximation. It results in two classes of modes: the TE-like and the TM-like modes which are supported by these waveguides. These modes are uncoupled under low-index-contrast conditions. In the case of silicon-on-insulator (SOI) waveguides, the coupling between them can no longer be neglected. This paper extends using the SOV to find analytical modal solutions of SOI-ROWGs. It expands these solutions in quadruples of plane waves and develops a novel non-paraxial scattering model to account for the polarization coupling between these waves under high-index-contrast conditions. This model yields approximate analytical expressions of the field components of the guided modes which are the sum of major and minor Marcatili’s TE-like and TM-like modal fields. Numerical examples show excellent agreement with the field components of full-vectorial mode solvers.

An S‐band sectoral waveguide (SWG) mode converter was presented for simulation and electromagnetic analysis. A mode‐matching technique (MMT) for the electromagnetic analysis of an SWG mode converter has been proposed. The problem of trifurcation of the coaxial waveguide to shape SWGs and bifurcation of SWGs is discussed. In this framework, the selections of appropriate testing modes at each junction are justified. The simulation time has improved and the complexity of the proposed problem has reduced by the proposed approach. The numerical results of the MMT are compared against simulation results and are found to be in good agreement. The efficiency of both the simulated and analyzed results shows a mode conversion efficiency higher than 98.0%. An experimental evaluation shows the mode conversion of TM01 to TE11 mode using far‐field radiation patterns and has been compared with simulation results. Also, the MMT and simulation validate the mode conversion of TM01 to TE11 mode.

Computational costs limit large scale reservoir simulations to coarse grid systems. Determination of an effective permeability for a simulation grid block requires a proper scale-up of small scale permeability heterogeneities within that grid block. Conventional scale-up techniques are limited to a diagonal tensor representation of effective permeability. Therefore, such techniques cannot handle general permeability anisotropy (full tensor) exemplified by cross-bedded permeability structures that may be present on a smaller scale. An analytical method is developed to calculate an effective permeability tensor for a grid block by accounting for small scale heterogeneities within the grid block. The method honors both the location and the orientation of the small scale heterogeneities. Effective permeability tensors calculated using the analytical method and a numerical method show excellent agreement. Miscible displacement simulations show that the effective permeability tensor method outperforms conventional scale-up techniques in predicting flood front locations in cases of general permeability anisotropy.

This paper presents a novel 1-to-N power division architecture combining overmoded mode waveguides and modular N-way waveguide-to-microstrip mode converters. By decomposing the mode field distribution along the narrow wall of a rectangular waveguide, the proposed design enables flexible power splitting into arbitrary output ports (even or odd numbers) through uniform sub--mode waveguide pathways. To achieve the above function using microwave transmission lines, a tapered transition structure ensures wideband excitation of the overmoded waveguide, while linearly tapered slot antennas (LTSAs) serve as N-way mode converters. Prototypes with two-, three-, and four-channel outputs demonstrate excellent amplitude-phase uniformity (≤0.5 dB amplitude imbalance and ≤ phase deviation) across 6.5–12 GHz, with return loss <−10 dB. The modular 1-to-N power divider enables the rapid reconfiguration of output channels by simply replacing the mode converter module.

In this paper, a novel approach based on the differential evolution algorithm is proposed for the optimal design of high-power millimeter-wave TM/sub 01/-TE/sub 11/ circular waveguide mode converters. The axes of the waveguide mode converters bent in one plane are represented by cubic B-splines, and the coordinates of the B-spline nodes are parameters to be optimized. Numerical optimization results show that the proposed approach can be used to design highly efficient mode converters with very short converter lengths. Furthermore, the input and output of the optimized mode converters can be in the same direction.

Recently, there has been some interest in planar or rectangular dielectric accelerating structures for future high-gradient linear accelerators. In this paper, we present a detailed analysis of the modes of a dielectric-loaded rectangular waveguide accelerating structure based on a circuit model approximation and mode matching method. In general, the acceleration field in a synchronous acceleration mode is nonuniform in the two transverse dimensions. We show, however, that by using a series of rectangular structures successively rotated by 90 degrees, the net accelerating force can be made almost uniform. Characteristic parameters such as R/Q, group velocity, and attenuation constant for X- and W-band accelerators are calculated. The longitudinal wakefields experienced by a relativistic charged particle beam in these structures are also presented. These analytical results are also compared with numerical calculations using the MAFIA code suite demonstrating the validity of our analytic approach.