Coaxial Waveguide Research Articles

Принципы реализации соосных СВЧ-соединителей для современных радиоэлектронных систем

Many modern radioelectronic systems are based on antenna arrays such as APAA (active phased array antenna) or DAAR (digital active array antenna), which require specialized connectors of new types and design solutions for the input/output of the microwave signal. The aim of this work is to improve the performance and reliability of coaxial microstrip connectors and coaxial waveguide transformer connectors of longitudinal type. The paper analyzes the arrangement principles of antenna feeders in modern radioelectronic systems with microwave connectors and substantiates the need to create new types of specialized microwave connectors. The authors demonstrate the issues that arise when using known coaxial microstrip connectors with threaded joints in antenna arrays. The paper considers the principles of implementing a cut-in microwave connector with hyperboloid contacts and its advantages, as well as the design of such a connector, i. e., the block coaxial microstrip transition and the cable part. The main technical parameters of cut-in microwave connectors are given. Using the analysis of the advantages and drawbacks of the known coaxial waveguide junction, the authors develop the requirements for the creating new microwave connectors of this type. The paper presents a design version of the longitudinal coaxial waveguide transformer connectors and their main characteristics.The considered design versions of the cut-in coaxial microstrip connector and the longitudinal coaxial waveguide transformer connector were manufactured and their characteristics were carefully studied. Analysis of the research results and measured parameters allow asserting that the proposed technical solutions are reliable, reproducible, can be mass produced, and thus can be recommended for use in modern radioelectronic systems.

Competitions among modes in magnetically insulated transmission line oscillator

<sec>As a compact and high power microwave source, the competitions among various modes are prone to appear in the initial stage of the development of the radiated electromagnetic field in a magnetically insulated transmission line oscillator (MILO). If the mode competitions are not controlled effectively, the output characteristics of the MILO may decline in the end. </sec><sec>As is well known, the operating mode of MILO is generally designed on the π mode of the TM<sub>00</sub> mode and the coaxial disk-loaded waveguide is usually adopted as a slow-wave structure for beam-wave interaction in MILO. Therefore from the dispersion relations between the electron beam and the lower order electromagnetic modes(including TM<sub>00</sub>, TM<sub>01</sub> and HEM<sub>11</sub> modes) in the slow-wave structure, the characteristics and possible suppression methods of the three kinds of mode competitions are analyzed simply. The first kind mode competition is between the different axial modes of the fundamental TM<sub>00</sub> mode. In this case, the electromagnetic field of the competition mode is also axially symmetric and its frequency is slightly lower than that of the π mode. The second is the competition between the TM<sub>00</sub> and higher order TM<sub>01</sub> mode. In this case, the competition frequency is rather higher than that of the π mode (TM<sub>00</sub>). The third is the competitions between the TM<sub>00</sub> and low order asymmetric HEM<sub>11</sub> modes. In this case, the competition frequency is slightly higher than that of the main mode. Appropriately choosing the radii of the anode vanes, the number of the anode cavity and the load length of the cathode, the corresponding mode competition intensity can be weakened. </sec><sec>Based on the obtained results above and the existing model of the MILO, a compact high output power L-band MILO is proposed. Numerical studies of the mode competitions and output characteristics are carried by using the three dimensional particle-in-cell code. Cold-cavity test shows that in the low frequency range, the easily stimulated electromagnetic modes are the π mode of TM<sub>00</sub> and HEM<sub>11</sub> modes with frequencies of 1.61 GHz and 1.77 GHz, respectively. The numerical results of hot-cavity verify that the competition in the initial stage comes mainly from the asymmetric HEM<sub>11</sub> mode due to the fact that there exists the strut in the output region, the Cartesian coordinates are adopted during the simulation, and totally symmetry cannot be guaranteed. In addition, electron beam emission from the cathode is not ideally even. But stable and high output microwave power is obtained in the end in the L-band MILO by being optimized. The output power and efficiency are 8.1 GW and 18% respectively, and the mode purity reaches about 97%. </sec>

A Novel High-Gain Sum and Difference Conical Beam-Scanning Reflector Antenna

A novel sum and difference (SD) conical beam-scanning reflector antenna is proposed in this paper. The reflector surface, illuminated by two omnidirectional horns, is a body of revolution obtained by revolving the generating parabola about a symmetry axis. The horns stacked along the symmetry axis of the reflector are fed by a nest coaxial waveguide. Teflon lens is used to improve the side lobe levels and reflection coefficients of the feed horns. By tilting the generating parabola and using the offset feeding method, two conical beams, with different beam pointing angles, were generated. A compact feed network was also designed to feed the two horns, which includes two rectangular TE10 mode-to-coaxial TEM mode transitions and a Magic-T to implement SD beams. The scanning performance of conical beams can be achieved by mechanically moving the feed antennas along the symmetry axis and taking full advantage of offset focus characteristic of the parabolic reflector. The error in angle measurement was also discussed. The SD conical beam-scanning antenna was formed by a parabolic dish with a radius of 18 λ operating at 24 GHz. The proposed antenna was designed, simulated, and fabricated. The measured results show that the difference beam null-depth is -25 dB and the sum beam gain is 15 dBi at 40°. The sum beam gain varies by less than 1.5 dB across the scan coverage from 30.8° to 45.2°. The measured results are found to be in good agreement with the simulated ones.

Bragg microwave structure in a coaxial waveguide as a sensor for monitoring the dielectric parameters of liquid media

Bragg microwave structure in a coaxial waveguide as a sensor for monitoring the dielectric parameters of liquid media

DETERMINATION OF THE GEOMETRIC SIZE OF THE COMMUNICATION HOLE OF TWO CYLINDRICAL WAVEGUIDES

It is always relevant to improve performance in electrodynamic systems. When solving problems on the electrodynamic characteristics of hollow coupled systems, the question is often asked about the relationship between them, about the form of the communication hole with a certain orientation of the guide axes in the system elements and its geometric dimensions. Such a system is a generator (small-sized local oscillator8 mmrange). The inclusion of a high-Q stabilizing resonator in the Gunn diode generator significantly improves its characteristics. The use of a low-quality coaxial chamber as a diode section increases the generation stability. However, this complicates the numerical calculations of the electrodynamic system of the generator due to the uncertain configuration of the communication hole, since it arises as a result of the intersection of two cylindrical volumes of a coaxial waveguide and a high-quality cylindrical resonator. In the present work, the task is determination of the shape and size of the intersection figure of two unequal radii of cylindrical volumes with axes orthogonally located in relation to each other at a distance. The resulting shape of the intersection figure in a planar approximation forms a flat ellipse. The larger diameter of the coupling ellipse depends on the diameter of the resonator, the smaller on the inner diameter of the coaxial chamber, depending on the distance between their axes. It is necessary to determine the equivalent rectangular hole of the connection. Its presence simplifies the construction of a tangent electric field at the communication hole, which is necessary for numerical calculations of the electrodynamic characteristics of the system. In this case, with constant diameters of the cylindrical resonators, the geometrical dimensions of the hole depend only on the distance between the axes. It is with this circumstance that they are dealing with the study of the connection between a cylindrical coaxial diode section and a high-Q stabilizing resonator. Unlike other circuits, where the diode is included in the waveguide section, in this case, its inclusion is made in a coaxial line.

Coaxial traveling-wave microwave reactors: Design challenges and solutions

Microwave chemistry applications have been investigated for more than three decades. Contrary to common cavity-based microwave applicators, the traveling-wave microwave reactor has the potential to enable the process scale-up, a better coupling of microwave energy with microwave-susceptible catalysts, and consequently highly uniform microwave heating. In this work, the engineering challenges entailed with the design of a traveling-wave microwave waveguide are explained and appropriate solutions developed. A new traveling-wave microwave reactor with a coaxial waveguide structure is presented. Simulation results show that there is no standing wave generated along the structure. Furthermore, in order to keep the impedance matching and minimize the microwave reflections while the reactor is loaded with catalyst samples, new reactor’s loading patterns are introduced. Simulation results showed that for the proposed method, microwave-susceptible catalytic fixed-bed could interact more efficiently with microwave energy and produce a uniform heating profile.

Compact three‐dimensional bandpass FSS with high selectivity based on split square coaxial waveguide

In this Letter, a compact three-dimensional (3D) frequency selective surface (FSS), exhibiting a bandpass filtering response with high selectivity, is proposed based on the split square coaxial waveguide (SSCW). The unit cell of the presented 3D FSS consists of one parallel-plate waveguide propagation path and one SSCW propagation path. In the SSCW path, two identical short SCWs are produced by employing a centred annular slot. Each short SCW intrinsically provides a square slot resonance. Owing to the electromagnetic coupling between these two square slot resonances, original single square slot resonant mode will split into even-/odd-resonant modes, resulting in a flat passband with two transmission poles. Moreover, two transmission zeros located at both sides of the passband are introduced for high selectivity, because the electromagnetic waves passing through these two different paths are combined out of phase. By investigating the electric-field distributions at the frequencies of the transmission zeros/poles, the operating principle of the proposed 3D FSS is described. A prototype of the proposed 3D FSS is fabricated and measured. The measured results show that the proposed design can achieve a stable response under the incident angles up to 60° for both TE and TM polarisations.

A High-Power and High-Efficiency Bend Overmode Coaxial Waveguide

A bend overmode coaxial waveguide with advantages of high-efficiency and high-power handling capacity is investigated. The principle of the proposed waveguide is as follows: the TEM mode in the coaxial waveguide is converted to TE11 modes of two 180° sector waveguides, and then the sector waveguide bends with a demanded turning angle, afterward the TE11 modes in the two sector waveguides are merged into the TEM mode of the coaxial waveguide. A C-band waveguide prototype with a center frequency of 4.0 GHz and a turning angle of 45 is designed and fabricated. The experiment results show that: the transmission loss of the fundamental mode at the center frequency is 0.2 dB and the VSRW is 1.1. When the frequency ranges from 3.8 to 4.2 GHz, the transmission loss of the fundamental mode is less than 0.4 dB and the VSWR is less than 1.5. The field distributions of this waveguide are analyzed through simulation, which prove its advantage of high-power handling capacity.

A high-efficiency dual-band relativistic Cerenkov oscillator based on dual electron beams

High efficiency and high frequency are key research topics for the development of high power microwave devices. There are, however, serious issues with mode competition in relativistic Cerenkov devices based on a single electron beam, which can lead to low efficiency in the beam-wave interaction process. In this paper, a high-efficiency relativistic Cerenkov oscillator based on a dual electron beam is proposed. The hollow slow wave structure is embedded in the inner conductor of the coaxial waveguide to obtain a double coaxial electromagnetic structure, which can suppress mode competition and improve the beam-wave interaction efficiency of the dual-band radiation. Moreover, each band of radiation is independent of the other, such that high frequency output radiation is generated. Using the particle-in-cell method, the physical processes involving the beam-wave interaction in the oscillator are studied with the aim of designing a high-efficiency double-electromagnetic structure. Simulation results indicated that the output power levels for the X-band and Ka-band were 1.50 GW and 710 MW, respectively, and the efficiencies were 34.7% and 30.7%, respectively, for a diode voltage of 550 kV and a guiding magnetic field of 0.85 T.

A Novel, Portable and Fast Moisture Content Measuring Method for Grains Based on an Ultra-Wideband (UWB) Radar Module and the Mode Matching Method.

To perform fast and portable grain moisture measurements under field conditions, a novel moisture sensor was designed, which consisted of a coaxial waveguide, a circular waveguide, and an isolation layer. The electromagnetic characteristics of the sensor were simulated and measured. The analytical model, which represented the relationship between the reflection coefficient of the sensor and the complex permittivity of grain, was established by using the mode matching method. The reflection coefficient of the sensor was measured by using an ultra-wideband (UWB) radar module, and the moisture content of grains was calculated from the complex permittivity by using density-independent model. To verify the performance of the proposed method, wheat, rough rice, and barley were taken as examples. The measured results in the range from 1.0% to 26.0%, wet basis, agreed well with the reference values (R2 was more than 0.99), and the maximum absolute errors for wheat, rough rice, and barley were 1.1%, 1.0%, and 1.4%, respectively. In addition, the effect of isolation layer was discussed. Both the simulation results and the experimental results showed that the isolation layer improved the stability of sensor.

Analysis and design of TEM-TE11 coaxial waveguide bend mode converters

AbstractTwo coaxial waveguide bend mode converters that transform coaxial transverse electromagnetic mode to TE11 coaxial waveguide mode are presented in this paper. Both converters are designed and optimized on the basis of the strictly derived mode coupling coefficients. Conversion efficiencies of both converters are over 99% and the power-handling capacities reach a gigawatt level. The combined dual-bend mode converter is fabricated and tested. The experimental results coincide well with the theoretical calculations and simulations, which demonstrates the feasibility of the designed converter.

Multi-channel bound states in the continuum in coaxial cylindrical waveguide

Bound states in the continuum (BICs) or embedded trapped modes are widely studied in different physical systems. The studies are restricted to a single open scattering channel. In the present paper we consider BICs embedded into several continua in a cylindrical resonator opened by two coaxially attached cylindrical waveguides with different radii. We demonstrate that engineering the BICs requires a degeneracy of three eigenmodeds of the closed resonator. That is achieved by variation of both the length and the radius of the resonator.

Analysis of multiplication characteristics of coaxial waveguide loaded ceramic under external magnetic field

In recent years, a lot of research work has been done on secondary electron multiplication studies in parallel plate structures. A nonuniform field may not only affect the results quantitatively but also lead to a new phenomenon. This paper presents a Monte Carlo model to investigate the multipactor discharge in a coaxial waveguide structure loaded ceramic window, which is applied to a high power coupler. In order to suppress secondary multiplication and improve the transmitting power of the high-power microwave window, the application of an external magnetic field is theoretically analyzed and simulated. A Monte Carlo algorithm is used to track the secondary electron position and study the multipactor scenario on the surface of a ceramic window in the coaxial line, including 3-D trajectory program and 3-D particle distribution program. It is demonstrated that an appropriate DC magnetic field can generate a compensating trajectory and collision, which suppresses the secondary electron avalanche effectively. The optimal value of the external magnetic field for avoiding the multipactor phenomenon is also discussed.

Analysis and design of a novel dual-band coaxial waveguide mode converter for high-power microwave applications

ABSTRACTBased on the derived coupling coefficients of the circular waveguide and coaxial waveguide, a novel dual-band serpentine coaxial mode converter is proposed in this paper. This dual-band converter consists of two parts: an inner inserted circular waveguide TM01-TE11 converter operating at Ka-band, and an outer coaxial waveguide TEM-TE11 converter working at Ku-band. The inner and outer converters have the same curvature distribution along the propagation direction with a structure length of 800 mm. Simulated results exhibit that the maximum conversion efficiencies of the inner and outer converters reach 98.7% and 98.9% at 35 and 15 GHz, respectively. The bandwidths of the inner and outer converter are 1.9 and 2.5 GHz when the conversion efficiency is over 90%. Furthermore, the dual-band mode converter has a symmetry and reciprocity structure with coaxial-parallel input/output port. The good agreement between theoretical calculations and simulation demonstrates the feasibility of this design.

Mode‐matching analysis for characterization of the sectoral waveguide mode converters

AbstractAn 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.

Multiscale Interfacial Characterisation of Transport Properties in Composite Li-Ion NMC532 Electrodes

Good ionic and electronic conductivities are required in battery electrodes to facilitate redox reactions and thus efficient charge and discharge of the battery. However, limitations of charge transport properties in state of the art lithium-ion positive composite electrodes greatly restrain the electrode thickness. This is largely attributed to: (i) the multitude of interfaces/contacts that arise with the different materials, and at different scales inside the composite electrode; and (ii) to the degree of percolation and tortuosity of the different phases. The active material studied, LiNi0.5Mn0.3Co0.2 O2 (NMC532), consists of 1µm size grains (or particles) that agglomerate to form 4µm clusters. The binding polymer PVDF is used with Carbon Black (CB) to impart higher electronic conductivity. The aim of this project is to study the effect of the electrode morphology and the various interfaces on electronic and ionic limitations. By changing the morphology of the electrode (i.e. composition and porosity) the aim is to minimize the transport limitations in the electrode [1]. In doing so it is hoped to be possible to increase electrode thickness and thus minimize the non-electroactive part in the battery electrodes, reducing cost and increasing efficiency. This research may also help in developing a faster method to optimize new active materials and thus reduce its time to market. Broadband Dielectric Spectroscopy (BDS) apply AC perturbations, between 20Hz to 18GHz in our case, across a metal coated sample at the end of a coaxial waveguide. Complex permittivity and conductivity (resistivity) are then calculated from admittance (low-frequency) and the coefficient of reflection (high-frequency). The inferred electric polarisations (or susceptibilities) at each interface are additive in nature. It provides information about multiscale charge transfer phenomenon across interfaces. This allows for a multi-hierarchical study of the composite. The interfacial characterisation of resistive and capacitive responses is carried out using Nyquist plots. Measurements are undertaken using dry nitrogen, from room temperature to -100°C. The conductivity of NMC532 is thermally activated and activation energies are derived using Arrhenius plots. To characterise the NMC532 active material alone, samples with no carbon black were referenced. Electrode metal contact, clusters and particles of NMC532 were characterised for dry samples. Samples were then impregnated with solvent and electrolyte to study their effect on the active material. Both conductivity and interfacial capacitance were seen to increase for the impregnated electrodes. Industrially fabricated NMC532 composite electrodes with varying CB content and porosity, coated on aluminium, were also characterised. It was seen that the electrochemical performance was better for electrodes with a non-percolated CB-polymer network The results obtained bring to question the necessity to have percolated electrodes when using an active material with relatively high conductivity. This is investigated with the help of electrochemical impedance spectroscopy (1mHz-50kHz) characterising the charge-transfer resistance as well as operando BDS, allowing for interfacial characterisation of electrodes at different levels of charge/discharge. The research is part of the project ANR Pepite comprising researchers conducting further characterisations such as FIB-SEM X-Ray tomography and PF-NMR to allow for a complete characterisation of the composite electrode and a better understanding on the effect of the electrode architecture on its performance. Acknowledgement We are grateful to the ANR for the funding of the Pepite project (ANR-15-CE05-0001).

Input and Output Couplers for an Oversized Coaxial Relativistic Klystron Amplifier atKa-Band

We propose a novel system of input and output couplers, excited in azimuthal symmetric and stable mode of operation, for an oversized coaxial relativistic klystron amplifier (OCRKA) at Ka -band. A mode converter is introduced in the output coaxial waveguide to provide a tunnel for the input waveguide and fix the inner and outer conductors of the OCRKA. After characterizing the proposed input and output couplers, the high-frequency structure of the OCRKA is designed and then optimized by Computer Simulation Technology. The simulated frequency and loaded quality factor of the input, output, and idler cavities are validated against measurement. Also, the beam–wave interaction of the OCRKA using the proposed input and output couplers is simulated by particle-in-cell software, the average saturated output power of 880 MW of the OCRKA at Ka -band, with 29.3% electronic efficiency and 58-dB saturated gain are obtained. Moreover, no pulse shortening of the output power waveform is observed during the simulation time of 100 ns, which indicates that the proposed input and output couplers can suppress the higher order mode self-oscillation in the Ka -band OCRKA studied here.

Enhancement of Complex Permittivity and Attenuation Properties of Recycled Hematite (α-Fe2O3) Using Nanoparticles Prepared via Ball Milling Technique.

The purpose of this study was to synthesize high-quality recycled α-Fe2O3 to improve its complex permittivity properties by reducing the particles to nanosize through high energy ball milling. Complex permittivity and permeability characterizations of the particles were performed using open-ended coaxial and rectangular waveguide techniques and a vector network analyzer. The attenuation characteristics of the particles were analyzed with finite element method (FEM) simulations of the transmission coefficients and electric field distributions using microstrip model geometry. All measurements and simulations were conducted in the 8–12 GHz range. The average nanoparticle sizes obtained after 8, 10 and 12 h of milling were 21.5, 18, and 16.2 nm, respectively, from an initial particle size of 1.73 µm. The real and imaginary parts of permittivity increased with reduced particle size and reached maximum values of 12.111 and 0.467 at 8 GHz, from initial values of 7.617 and 0.175, respectively, when the particle sizes were reduced from 1.73 µm to 16.2 nm. Complex permeability increased with reduced particle size while the enhanced absorption properties exhibited by the nanoparticles in the simulations confirmed their ability to attenuate microwaves in the X-band frequency range.

Highly accurate and numerically stable computations of double-layer coaxial waveguides

PurposeThe purpose of this study is to develop and investigate a fast and accurate algorithm for the modeling of characteristic impedance of double-layer coaxial waveguides.Design/methodology/approachThis paper presents the newly developed numerically stable analytical formula for calculation of the characteristic impedance of double-layer coaxial conductor and its elements such as resistance, inductance, capacitance and conductance per unit length. The formula contains modified scaled Bessel functions. The results of the developed analytical formula were compared with results obtained from the axis-symmetric 2D and 3D finite element method (FEM) simulations, using three different solvers.FindingsThe proposed method shows a good agreement between results obtained with the new fast and stable analytical model and particular FEM models, selected depending on frequency range. The relative difference between characteristic impedance calculated using the new analytical method and obtained from chosen FEM method for discussed frequency range is less than 0.1 per cent which proves the correctness of the new analytical formula. Noteworthy is the fact that the relative difference of the resistance computed using the developed analytical method and obtained with Maxwell FEM solver for the frequency in range from 1 Hz to 10 MHz is less than 0.01 per cent. The presented work shows that when the calculations are performed over wide frequency range, it is necessary to use more than one solver, especially when the wavelength is comparable with dimensions of the conductor. The computation time of the new analytical model is much shorter than the computation time of FEM.Originality/valueAn efficient, numerically stable algorithm for computation of characteristic impedance of a double-layer coaxial conductor (waveguide).

Design and performance comparison of a novel high Q coaxial resonator filter and compact waveguide filter for millimeter wave payload applications

A novel high-performance high Q filter with ultra-wide spurious-free stopband and thermally stable performance is introduced using higher order mode of the coaxial resonator. The 7-pole Chebyshev and a 5-pole cross-coupled filter are designed at Ka-band to validate the concept. A compact cross-coupled waveguide filter is introduced with a different approach to realize cross-coupling makes the filter compact. The coaxial resonator and waveguide resonator filter have the same configuration, and their performances are compared at ambient and over the temperature. The high power analysis is done for both these filters to find their power handling capability. The high power performance of the coaxial resonator filter is superior, and it can handle 45.525 kW peak power. This filter is suitable to be used as pre-select filter in millimeter wave payloads as well as for high power filtering applications.