Meander-line Slow-wave Structure Research Articles

A Ka-Band Angular Log-Periodic Meander-Line SWS Supported by Diamond Rods

The angular log-periodic meander-line traveling wave tube (TWT) is a kind of low voltage, small-sized, high power, low cost, on chip amplifiers, and considered as a key part of the advanced communication systems, the future biomedical applications and the next electronic counter measure (ECM) instruments <i>et al.</i> Here, an angular log-periodic meander-line TWT is presented in this article. The angular log-periodic meander-line slow wave structure (SWS) is supported by two diamond rods. The dispersion and the impedance characteristics are analyzed in detail. In order to reduce the reflection loss, a gradual ridged waveguide is connecting the input&#x2013;output standard rectangular waveguide to the meander-line SWS. The particle in cell (PIC) simulations show that the output power of the TWT can reach 55 W at 34 GHz with the operation voltage of 1800 V and the beam current of 0.2 A. The SWS is manufactured by a laser machine with Molybdenum sheet. The assembled TWT is tested and the results show that the <inline-formula> <tex-math notation="LaTeX">${S}_{{11}}$ </tex-math></inline-formula> is less than &#x2212;10 dB at 30&#x2013;39 GHz. The <inline-formula> <tex-math notation="LaTeX">${S}_{{21}}$ </tex-math></inline-formula> mismatch between the simulated and the measurement is discussed at the end.

Design Study on a Multiple-Tunnel Meander-Line Slow-Wave Structure for a High-Power V-Band Traveling-Wave Tube

Nowadays, there is a strong interest in miniature and high-power vacuum electron devices (VEDs) operating in millimeter and sub-THz bands. VED sources of coherent sub-THz radiation are required for many applications, especially for future advanced high-data-rate telecommunication systems. In this work, we present the results of design study of a meander-line slow-wave structure (SWS) suitable for multiple-sheet-beam operation to achieve a high level of output power. The results of cold-test electromagnetic simulation show a possibility of operation at beam voltage of 12 kV with high values of interaction impedance up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$12 \Omega $ </tex-math></inline-formula> . The 3-D particle-in-cell simulation of performance of the traveling-wave tube with 400-mA, 12-kV multiple sheet electron beam predicts up to 26-dB gain and up to 376-W output power.

Beam–Wave Resynchronization Method of the Nonperiodic Meander Line and Folded-Waveguide SWS for TWTs

A beam-wave resynchronization (BWRS) method is proposed by changing the structural parameters of the nonperiodic (NP) slow wave structure (SWS) to reduce the phase velocity of the wave for traveling-wave tubes (TWT) application. The mathematical model and analysis for the BWRS method are introduced to investigate what condition the NP meander line SWS (ML-SWS) and the NP folded-waveguide SWS (FW-SWS) should satisfy so that the corresponding TWT can have a good output performance. As the applications, the NP zigzag ML-SWS and the concentric arc FW-SWS are designed according to the method, which is also compared with that designed according to the phase velocity synchronization (PVS). The simulated results show that, by using the BWRS method, the max output power (efficiency) of the zigzag ML-SWS TWT can be improved from 56.7 (18.9%) to 76.26 W (25.4%), and the bandwidth can be expanded from 6 to 10 GHz in the Ka-band. Furthermore, the max output power (efficiency) of the concentric arc FW-SWS TWT can be improved from 199 (27.6%) to 237 W (32.9%), and the bandwidth can be expanded more than twice in the W-band as before. These results indicate that the BWRS method is beneficial for the improvement of the output power and electron efficiency and may be beneficial for wider bandwidth.

Multiple Dielectric-Supported Ridge-Loaded Rhombus-Shaped Wideband Meander-Line Slow-Wave Structure for a V-Band TWT

A multiple dielectric-supported ridge-loaded rhombus-shaped meander-line (MDSRL-RSML) slow-wave structure (SWS) is proposed for a V-band wideband traveling wave tube (TWT). The high-frequency and transmission characteristics of the SWS are investigated. The proposed structure can realize stable output via attenuator and special phase-velocity jumping. Particle-in-cell (PIC) results indicate that, for a 7 kV, 0.1 A sheet-beam, the average output power can reach 60 W at 60 GHz and a 3 dB bandwidth of 9 GHz, with the corresponding gain and electron efficiency of 30.8 dB and 17.2%, respectively. Compared with the dielectric-supported rhombus-shape meander-line (DS-RSML) SWS, the proposed structure has a wider bandwidth, higher gain, more stable structure, and better heat dissipation ability, which make it a good candidate source in millimeter-wave communications.

Green’s Functions of Multi-Layered Plane Media with Arbitrary Boundary Conditions and Its Application on the Analysis of the Meander Line Slow-Wave Structure

A method was proposed for solving the dyadic Green’s functions (DGF) and scalar Green’s functions (SGF) of multi-layered plane media in this paper. The DGF and SGF were expressed in matrix form, where the variables of the boundary conditions (BCs) can be separated in matrix form. The obtained DGF and SGF are in explicit form and suitable for arbitrary boundary conditions, owing to the matrix form expression and the separable variables of the BCs. The Green’s functions with typical BCs were obtained, and the dispersion characteristic of the meander line slow-wave structure (ML-SWS) is analyzed based on the proposed DGF. The relative error between the theoretical results and the simulated ones with different relative permittivity is under 3%, which demonstrates that the proposed DGF is suitable for electromagnetic analysis to complicated structure including the ML-SWS.

Design Method of the Non-Periodic Meander Line and Folded-Waveguide SWS for TWTs Based on the Effective Phase Velocity Synchronization

A design method of the non-periodic meander line slow-wave structure (ML-SWS) and folded-waveguide slow-wave structure (FW-SWS) for traveling-wave tubes (TWTs) is proposed based on effective phase velocity synchronization. For the non-periodic ML-SWS and FW-SWS, the unified effective axial phase velocity seen by electrons, the dispersion equation, and the ideal beam-wave synchronization voltage are derived. The theoretical results demonstrate that the non-periodic ML-SWS and FW-SWS reported to date are consistent with the proposed method. Furthermore, two examples are presented as applications for the proposed method to the non-periodic SWS design, including the concentric arc FW-SWS and the zigzag ML-SWS. In addition, the simulated results of the two examples are in good agreement with the theoretical ones.

Inverse Design of a Microstrip Meander Line Slow Wave Structure with XGBoost and Neural Network

We present a new machine learning (ML) deep learning (DL) synthesis algorithm for the design of a microstrip meander line (MML) slow wave structure (SWS). Exact numerical simulation data are used in the training of our network as a form of supervised learning. The learning results show that the training mean squared error is as low as 5.23 × 10−2 when using 900 sets of data. When the desired performance is reached, workable geometry parameters can be obtained by this algorithm. A D-band MML SWS with 20 GHz bandwidth at 160 GHz center frequency is then designed using the auto-design neural network (ADNN). A cold test shows that its phase velocity varies by 0.005 c, and the transmission rate of a 50-period SWS is greater than −5 dB with the reflectivity below −15 dB when the frequency is from 150 to 170 GHz. Particle-in-cell (PIC) simulation also illustrates that a maximum power of 3.2 W is reached at 160 GHz with 34.66 dB gain and output power greater than 1 W from 152 to 168 GHz.

Study of an Attenuator Supporting Meander-Line Slow Wave Structure for Ka-Band TWT

An attenuator supporting meander-line (ASML) slow wave structure (SWS) is proposed for a Ka-band traveling wave tube (TWT) and studied by simulations and experiments. The ASML SWS simplifies the fabrication and assembly process of traditional planar metal meander-lines (MLs) structures, by employing an attenuator to support the ML on the bottom of the enclosure rather than welding them together on the sides. To reduce the surface roughness of the molybdenum ML caused by laser cutting, the ML is coated by a thin copper film by magnetron sputtering. The measured S11 of the ML is below −20 dB and S21 varies around −8 dB to −12 dB without the attenuator, while below −40 dB with the attenuator. Particle-in-cell (PIC) simulation results show that with a 4.4-kV, 200-mA sheet electron beam, a maximum output power of 126 W is obtained at 38 GHz, corresponding to a gain of 24.1 dB and an electronic efficiency of 14.3%, respectively.

A Concentric Arc Meander Line SWS for Low Voltage, High Efficiency, and Wide Bandwidth V-Band TWT With Dual Sheet Beam

A concentric arc meander line slow wave structure (CAML-SWS) for low voltage, high efficiency, and wide bandwidth V-band traveling wave tube (TWT) with dual sheet beam (DSB) is proposed. As a nonperiodic SWS, the CAML-SWS is utilized for obtaining low operational voltage and wide bandwidth performance. The DSB is employed for efficiency enhancement. The simulated reflection loss (|S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>11</b></sub> |) is smaller than -30 dB covering the whole V-band. The 3-D particle-in-cell (PIC) simulation predicts that the output power of the proposed TWT can reach 58.6 W at 60 GHz, when the voltage is set at 940 V and the current of each sheet beam is 0.1 A. The corresponding peak gain and electron efficiency is 19.6 dB and 31.1% at 60 GHz, respectively. Furthermore, the 3-dB gain bandwidth is about 17 GHz from 51 to 68 GHz, where the output signal is steady and the frequency spectrums are quite clean.

A Novel Coplanar Slow-Wave Structure for Millimeter-Wave BWO Applications

A novel coplanar slow-wave structure (SWS) for application in millimeter-wave backward-wave oscillator (BWO) is proposed in this article. Unlike the traditional microstrip meander-line SWS with metal layers on both top and bottom surfaces of the substrate, the proposed SWS has a metal layer only on the top surface of the substrate. This significantly reduces the dielectric loading effect. The SWS is quite suitable for fabrication using PCB or microfabrication techniques and can be directly fed with coplanar waveguide (CPW), which has a lower loss than microstrip line. A design of the SWS presented here covers a -15-dB S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> frequency range from 13.7 to 120 GHz. Simulation results for a BWO based on the proposed SWS show a tunable frequency range of 32.7 GHz and a maximum output power of 22.7 W at 114 GHz. To verify the proposed concept, a scaled version of the SWS is fabricated and measured S-parameters are presented. With a good potential for fabrication using microfabrication techniques, this structure can be a good candidate for millimeter-wave BWO applications.

Experimental Validation of Phase Velocity and Interaction Impedance of Meander-Line Slow-Wave Structures for Space Traveling-Wave Tubes

Meander lines are promising slow-wave structures (SWSs) for millimeter-wave traveling-wave tubes (TWTs) due to low-cost manufacture, low-voltage operation, and high interaction impedance. However, experimental results on meander lines are rare in the literature. Phase velocity and interaction impedance are the most important parameters for the design and characterization of TWT SWSs. Their experimental determination in meander lines is crucial for validating simulations and developing new topologies. Based on a new theoretical model, this article presents an experimental procedure to determine the phase velocity and the interaction impedance. The method is validated on four different Ka -band (33–37 GHz) meander-line SWSs, including two of a novel topology.

Development of microfabricated planar slow-wave structures on dielectric substrates for miniaturized millimeter-band traveling-wave tubes

We report the results of the design, simulation, fabrication, and cold-test measurements of millimeter-band 2D planar microstrip slow-wave structures (SWSs) on dielectric substrates. Such structures have a high slow-wave factor, which allows for low-voltage operation and reduction in the size and weight of the device. A low-cost and flexible fabrication technology based on magnetron sputtering and subsequent laser ablation has been developed and is reported in the paper. Microstrip meander-line SWS circuits at V-, W-, and D-bands have been fabricated and characterized. The fabrication of ring-bar planar SWSs by the photolithographic method is also discussed. Experimental measurement of S-parameters of the fabricated structures reveals good transmission properties. Return loss (S11) does not exceed −10 dB and attenuation is about 2 dB/cm in the V-band, 10 dB/cm in the W-band, and 8.5 dB/cm in the D-band.

Meander-Line Slow-Wave Structure on Dielectric Substrate for a Millimeter-Band Traveling-Wave Tube

A novel planar microstrip meander-line slow-wave structure (SWS) on dielectric substrate for a miniature low-voltage millimeter-band traveling-wave tube (TWT) with a high-aspect-ratio sheet electron beam is proposed. Main electromagnetic parameters of the SWS were studied. Using of such a slow-wave structure may lead to increase of the gain and output power of the TWT amplifier.

Study on an X-Band Sheet Beam Meander-Line SWS

The miniaturized traveling wave tube (TWT) is a kind of high-efficiency, high-power, long-lifetime power amplifier which is an attractive choice for many applications, such as outer space exploration, phased array radar detection, unmanned aerial vehicle (UAV) communication, and on-chip application. In this article, a sheet beam miniaturized TWT with V-shaped meander-line slow wave structure (SWS) supported by two trapezoidal ceramic rods is designed. First, the dispersion characteristics, the impedance characteristics, and the S-parameters of the V-shaped meander-line SWS are analyzed in detail. Then, the particle-in-cell (PIC) simulation results predict that the TWT can produce 512-W output power driven by a 7.1 kV, 0.3-A sheet beam with a rectangular cross-sectional area of 3.5 mm $\times0.1$ mm. The TWT can cover the whole ${X}$ -band when the operation voltage shift from 7.1 to 9.1 kV. At last, the V-shaped meander-line SWS is manufactured, assembled, and tested. The good agreement between the simulated and the measured ${S} _{\mathbf {11}}$ has been achieved and the mismatch between the simulated and the measured ${S} _{\mathbf {21}}$ has been discussed at the end.

Investigation on a Ka Band Diamond-Supported Meander-Line SWS

The microstrip meander-line traveling wave tube (TWT) is a kind of small sized, low voltage, low cost, and easy to fabricate TWT. It is an attractive choice for many applications, such as communication systems, phased array radars, security detectors, and electronic counter measure (ECM) instruments. In this paper, a Ka band U-shape meander-line slow wave structure (SWS) supported by a diamond rod is presented. The dispersion characteristics of this meander-line SWS are analyzed using CST MW Studio. The S-parameter simulation results show that the reflection is below − 15 dB between 32 and 38 GHz, and the particle-in-cell (PIC) simulation reveals that this meander-line TWT can produce 57 W output power at 36 GHz, when it is driven by a 8.1 kV, 0.04 A sheet beam with rectangular cross-sectional area of 1.0 mm × 0.12 mm. This meander-line SWS is manufactured, assembled, and tested. The good agreement between the simulated and measured S11 has been achieved and the mismatch between the simulated and measured S21 has been discussed at the end.

Theory, Simulation, and Analysis of the High-Frequency Characteristics for a Meander-Line Slow-Wave Structure Based on Field-Matching Methods With Dyadic Green’s Function

A field-matching method with dyadic Green’s function was presented in this article for analyzing the high-frequency characteristics of a meander-line slow-wave structure (ML-SWS). The effects of the metal shield and the thickness of the meander line were considered in the theoretical model. The theoretical results with five modes were calculated and compared with the simulated ones. The relative error in each phase shift was obtained, which demonstrates that theoretical calculated and simulated results are in good agreement. The conditions of band gap and crossing of neighboring modes were discussed. The effects of the thickness variation on high-frequency characteristic of the ML-SWS were also analyzed. In addition, some problems resulted in the confusion between different modes were also analyzed and discussed.

Замедляющая система меандрового типа на диэлектрической подложке для лампы бегущей волны миллиметрового диапазона

А novel planar microstrip meander-line slow-wave structure (SWS) on dielectric substrate for a miniature low-voltage millimeter-band traveling-wave tube (TWT) with a high-aspect-ratio sheet electron beam is proposed. Main electromagnetic parameters of the SWS were studied. Using of such a slow-wave structure may lead to increase of the gain and output power of the TWT-amplifier

Meander-Line Slow-Wave Structure for High-Power Millimeter-Band Traveling-Wave Tubes With Multiple Sheet Electron Beam

For advanced telecommunications and radar systems, high-power miniaturized millimeter-band traveling-wave tubes (TWTs) are required. In this letter, we propose a meander-line slow-wave structure (SWS) that is suitable for multiple sheet beam interaction that helps achieve high power. The simulation of cold electromagnetic parameters of the V-band SWS demonstrates good transmission characteristics, wide bandwidth, and high interaction impedance. Hot performance of the V-band TWT amplifier with the proposed SWS is also studied. The 3-D particle-in-cell (PIC) simulation predicts that the designed circuit yields a stable gain in the 50 – 70 GHz frequency range with a 25 – 30-dB small-signal gain. 250-W average output power is attained from a 1.5 – 2.0-W input driving signal at 68.1 GHz.

$Ka$ -Band Symmetric V-Shaped Meander-Line Slow Wave Structure

A symmetric configuration of two V-shaped microstrip meander-line slow wave structures (MLSWSs) is studied for application in Ka -band traveling-wave tubes (TWTs). Simulated dispersion characteristics and coupling impedance are presented for an optimized design. Particle-in-cell (PIC) simulation results show that for a 3.6-kV, 50-mA sheet-beam, the output power can potentially reach 28 W at 32 GHz with a gain of 28- and a 3-dB bandwidth of about 25% centered at 32 GHz. The proposed configuration is realized by first microfabricating a number of V-shaped MLSWSs on a 4” quartz wafer and then laser-dicing individual SWSs. A metal enclosure with waveguide input-output couplers is fabricated to house the SWSs and facilitate measurements. With two of the SWSs placed symmetrically inside the metal enclosure, the measured S11 for a 150-period symmetric MLSWS is better than -15 dB over 24-40 GHz. The reasons for the measured S21 being higher than expected are identified and verified by measurements on another set of SWSs which is fabricated using printed-circuit technique. An assembly that can be used for hot-tests is also presented.

Study of a miniaturized dual-beam TWT with planar dielectric-rods-support uniform metallic meander line

A dual-beam planar dielectric-rod-support uniform metallic meander line slow-wave structure (SWS) for high-efficiency Ka-band traveling wave tube (TWT) is proposed in this paper. Two dielectric rods are placed on both sides of metallic meander line to support it, instead of the dielectric substrate in the conventional microstrip meander line. Furthermore, it can not only solve the problem of the electron charge accumulation on microstrip but also leads to a bigger interaction impedance. According to particle-in-cell simulation results, a dual-sheet-beam planar dielectric-rod-support uniform metallic meander line TWT can get an output power of 330.2 W at 38 GHz under the case of 10.6 kV beam voltage and 0.2 A beam current. The corresponding maximum gain and electron efficiency are 23.4 dB and 15.5%, respectively, where the length of whole SWS is only 20 mm.