Mode H 01 in a sectoral waveguide

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>

The computer‐aided analysis and design of direct‐coupled and quarter‐wave‐coupled bandpass filters utilizing monomode rectangular waveguides with 1‐dimensional offset discontinuities are described. The equivalent networks of these discontinuities, which consist of a shunt reactance and additional transmission lines connected at both sides, have been derived from the rigorous field‐theoretical investigations of E‐plane and H‐plane displacements in rectangular waveguide. Both network elements are tabulated in terms of geometry and wavelength with fine steps to allow accurate interpolation by means of computational methods, Simple design formulae for the filter geometry as a function of the electrical specifications are given which are based upon narrow‐band approximations. The analytical relationships required for a computer simulation of the filter's wide‐band performance are summarized. The predicted frequency characteristics showed such close agreement with the experimental results obtained on two X‐band filter models that neither tuning elements in the waveguide sections nor final adjustments of the offset widths had to be provided.

Increasing of power with the retained high beam quality is one of the major directions of industrial cutting lasers improvement. CO2 lasers permit to produce the cut of perfect quality and are at the moment the most spread cutting lasers. The factor limiting the power of gas-flow CO2 lasers is the low mode volume of the stable resonator. Low order mode generation is necessary to guarantee that the BPP (beam parameter product) does not exceed the value needed for the qualitative cutting (about 6). We have optimized the self-filtering unstable resonator, SFUR applied to the gas-flow CO2 laser. It has been shown that the SFUR can provide the higher power (about 2…3 times) comparing to the stable resonator due to the bigger volume of the low order mode. The SFUR beam BPP value approaches to the low order mode of the stable resonator. Numerical calculations have been used to compare the aberration sensitivity of the SFUR and stable resonator. The SFUR beam spatial structure differs from TEM00 or TEM01* modes of the stable resonator. In the far field, the SFUR beam has weak diffraction rings, which can affect the cutting quality. The experiments on cutting were carried out with a transverse-flow laser with SFUR. The main experiments have been performed for mild steel up to 25 mm thick. Stainless steel and titanium have also been cut. The results have revealed that SFUR beam peculiarities do not affect the cutting quality. The kerf width and roughness of the cut samples approach to the values typical for the CO2 laser with the stable resonator. Titanium plates of 30 mm thick have been cut at the radiation power of 6 kW.

A new polarization filter with no element inside the circular waveguide is presented. It is realized by the insertion of rectangular waveguide sections in a circular waveguide. The validity of this new design is verified on a prototype model.

Utilization of graphene covered waveguide inserts to form tunable waveguide resonators is theoretically explained and rigorously investigated by means of full-wave numerical electromagnetic simulations. Instead of using graphene-based switching elements, the concept we propose incorporates graphene sheets as parts of a resonator. Electrostatic tuning of the graphene surface conductivity leads to changes in the electromagnetic field boundary conditions at the resonator edges and surfaces, thus producing an effect similar to varying the electrical length of a resonator. The presented outline of the theoretical background serves to give phenomenological insight into the resonator behavior, but it can also be used to develop customized software tools for design and optimization of graphene-based resonators and filters. Due to the linear dependence of the imaginary part of the graphene surface impedance on frequency, the proposed concept was expected to become effective for frequencies above 100 GHz, which is confirmed by the numerical simulations. A frequency range from 100 GHz up to 1100 GHz, where the rectangular waveguides are used, is considered. Simple, all-graphene-based resonators are analyzed first, to assess the achievable tunability and to check the performance throughout the considered frequency range. Graphene–metal combined waveguide resonators are proposed in order to preserve the excellent quality factors typical for the type of waveguide discontinuities used. Dependence of resonator properties on key design parameters is studied in detail. Dependence of resonator properties throughout the frequency range of interest is studied using eight different waveguide sections appropriate for different frequency intervals. Proposed resonators are aimed at applications in the submillimeter-wave spectral region, serving as the compact tunable components for the design of bandpass filters and other devices.

Latching phase shifters, consisting of a waveguide section containing a ferrite toroid, are widely used as digital steering elements in microwave array antennas. The theoretical determination of device performance cannot be obtained exactly, since these structures are inhomogeneous along both transverse directions. The present study presents an approximate method to evaluate phase shift and losses in the case of a rectangular toroid. An approximately equivalent structure (twin slab), for which an exact resolution method is available, is considered first. The changes due to the upper and lower sections of the toroid are then evaluated by means of a variational principle. Experimental results show good agreement with computed values for several practical cases considered. Finally, the range of validity for this approximate method is determined.

Several RF and microwave radiating devices, such as horn antennas, Fabry–Perot cavity antennas, and aperture-fed focusing devices, are excited through rectangular waveguides. The impedance matching of the overall system (from the waveguide feed to the radiating aperture) is a task of crucial importance that is often addressed by means of brute-force parameter-sweep full-wave analyses or blind optimization algorithms. In both cases, a significant amount of memory and time resources are required. For this purpose, we propose here a simple, yet effective solution, which only requires a single full-wave simulation and a semi-analytical procedure. The former is used to retrieve the antenna input impedance at the end of the waveguide port excitation. The semi-analytical procedure consists in a transmission-line equivalent circuit that models two waveguide discontinuities (namely two capacitive irises) within the waveguide section, whose position and geometric features are finely tuned to obtain a satisfactory impedance matching around the working frequency. The proposed method is shown to be effective in diverse and attractive application-oriented contexts, from the impedance matching of a Fabry–Perot cavity antenna to that of a wireless near-field link between two aperture-fed focusing devices. A remarkable agreement between full-wave simulations and numerical results is found in all cases. Thanks to its versatility, simplicity, and a rather low demand of computational resources, the proposed approach may become an essential tool for the effective design of waveguide-fed antennas.

Rectangular waveguide section with two partial-height transversal inserts located side by side is examined. Such a section acts as a resonator providing two transmission zeros and one transmission resonance located between these zeros simultaneously. Thus, the number of transmission zeros is twice more than the number of waveguide sections. The broadband quarter-wavelength resonator filter using such sections provides two stopbands and one passband simultaneously. Their bandwidths and locations are controlled both by the section geometry and the distance between the sections. Two closely spaced sections providing two independent stopbands are proposed as a perspective block for a filter with complicated frequency response.

The physical processes occurred in the waveguide-dielectric structure that has the form of a section of rectangular cut-off waveguide with dielectric insertion, which completely fills the cross section of the waveguide have been considered. The electromagnetic fields in the classic waveguide-dielectric resonator without devices for its excitation and a coupling element with two sections of the cut-off waveguide have been calculated. The expressions for the reflection and transmission coefficients of the structure under consideration are presented. The positions of poles and zeros of the reflection coefficient have been investigated with a fractional-rational approximation and they have been compared with the natural frequencies. The obtained results are useful for measuring the properties of dielectric materials with the aid of waveguide methods.

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>

Summary form only given, as follows. A comparison analysis of electromagnetic structures-a section of a constant cross-section finite length cut-off waveguide (CCSCW) and a section of a stepped cross-section cut-off waveguide (SCSCW) is presented. A design algorithm of the mentioned structures has been devised. In the present paper, the results of a solution of the problem of rectangular waveguide coupling through such structures are presented. By using the mode matching technique applied for eigenfields at the waveguide junction boundary, the integral equation set has been converted into a matrix equation. Here a Galerkin variational method, whose solution determines the values of the tangential electric field in the openings, is used. The convergence of the obtained solution to the exact one has been proved. Using such a design approach, the structures tunable by magnetic field: ferrite and ferrite-waveguide resonators in CCSCW and SCSCW are considered. A method is presented for calculating the elements of the scattering matrix, the absorption coefficients, the width of the passband, and the resonant frequency of a system consisting of ferrite and ferrite-waveguide resonators. Analytic relationships are derived and graphical dependencies are obtained, which provide an engineering computation to be performed for various designs of ferrite films. The utilization of compound ferrite dielectric plates for the linearization of the field frequency characteristic is shown.

We have passively Q- switched and mode locked a Neodymium doped fiber laser with a semiconductor saturable absorber minor (SESAM). The fiber used has an annular shaped active region (M-profile fiber) Fig.1a, possessing the advantage that the pump light may be completely absorbed over a short length. Butt coupling a SESAM at one of the fiber ends is therefore possible because there is no pump light left leading to an unwanted saturation of the absorber. We have made a modal analysis in the scalar approximation comparing the absorption of the M-profile fiber and a standard double clad one provided high power diode lasers are used for optical pumping. Figs.1b give examples of LPm p modes of a M-profile fiber. In the calculations the following parameters were used: pump wavelength λ= 8o3 nm, Δcorc-first cladding = 0.003 and Δfirst-second cladding = 0.04; 1)M-profile fiber: 5 µm ring width and 85 µm ring centre diameter; 2) double clad fiber: 100 µm pump core diameter, 6.5 µm doped core diameter. For the M-profile fiber not only the low order modes i.e. LP01 interact strongly with the doped region but higher order modes do as well. For the double-clad fiber it is only the field of the very low order modes (here LP0 1,) have an overlap with the active material whereas all higher order modes have almost nothing. Based upon the theoretical findings we have realised a set-up where the SESAM is directly attached to the fiber just as the incoupling mirror. Such an optical scheme has not been realised up till now as we believe. The SESAM was polished at the back side possessing a reflectivity of about 98%. The fiber length was 200 cm, the amount of pump radiation leaving the fiber was less than 5%. The measured pulse width using a fast detection electronics ( risetime 60 ps ) is shown in Fig. 1c. For a certain range of pump powers we have obtained Q-switch pulses with a very low jitter (&lt; 1% ). Locking a large bandwidth could not be achieved being partially due to the SESAM and to the multimode behaviour ( azimuthal direction ) of laser.

The dynamics of valve train is influenced by stiffness, size and mass distribution of its components and initial valve clearance and so on. All the factors should be taken into consideration correctly by dynamic model and described qualitatively and quantitatively through mathematical variables. This paper proposes a new simplified method for valve train components, namely mode matching method (MMM) for camshaft, pushrod, rocker arm, valve and valve spring. In this method the amount of lumped masses for each flexible component is determined based on its natural frequencies and the considered frequency range. As a result, the dynamic model of each component is required to match its low order modes within the considered frequency range. The basis of this method is that the contributions of each component to valve train vibration are mainly in the low order modes. The numerical model of valve train is verified by an experiment conducted on a motor driven valve train system.

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.

The authors study the interference that occurs between the high-frequency and low-frequency portions of a proposed dual-band antenna when the antennas transmit into free space or into an inhomogeneous plasma layer. They analyze two limiting cases, namely, (1) when the apertures of the antenna are backed by infinite waveguide sections, and (2) when the apertures are backed by cavities and the rectangular cavity contains a probe in it and the ridged waveguide section does not. Numerical examples are presented. >