Planar Slow-wave Structure Research Articles

Investigation of an X-band Cerenkov-type high power microwave oscillator driven by sheet electron beam

An X-band Cerenkov-type high power microwave (HPM) oscillator driven by a sheet electron beam is proposed and designed in this paper. In order to improve the efficiency of simulation optimization, a research method is proposed in which the large caliber coaxial Cerenkov-type HPM oscillator is taken as an initial model, which is equivalent to that of the planar slow-wave structure (SWS) by using the similarity between the planar SWS and the large caliber coaxial SWS. In addition, the effectiveness of the equivalent method is verified from the geometric structure, the field distribution of the operating mode, dispersion characteristics, and the preliminary particle simulation results of two devices. Based on the results of an X-band large caliber coaxial Cerenkov-type HPM oscillator, an X-band Cerenkov-type HPM oscillator driven by a sheet electron beam is investigated by the 3D particle-in-cell code. The simulation results show that the power conversion efficiency can reach 26.1% at the frequency of 11.9 GHz with the output power of 0.3 GW, while the sheet electron beam has the energy of 486 kV and it carries the current of 2.4 kA conducted by the magnetic field of 2.5 T.

Design of RF Planar Slow Wave Interaction Structure for THz Devices

Micro fabricated planar slow wave structure (SWS) in a travelling wave tube (TWT) has shown a superior performance when compared with the circular helix structure for RF power amplification. The circular helix structure applications are limited to the maximum operating frequency of 70 GHz. In the proposed paper, a rectangular planar slow wave structure operating at terahertz (THz) is designed. Fabrication of the beam interaction system is complex especially operating at higher frequencies as the device dimensions decrease. Use of planar interaction system simplifies the miniaturised fabrication process. The present paper focused on the design of staggered double vane slow wave structure (SWS) and simulated the corresponding dispersion diagram and S-parameters of the model by using CST Studio Suite software. The results for designed RF planar slow wave structure are then analysed.

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.

Dielectric-Supported Staggered Dual Meander-Line Slow Wave Structure for an E-Band TWT

In this article, a novel dielectric-supported staggered dual-meander-line (DS-SDML) planar slow-wave structure (SWS) is proposed for a traveling wave tube (TWT) working at E-band. The proposed staggered arrangement of meander-lines (MLs) leads to a stronger beam-wave interaction and achieves higher output power as compared to the symmetric arrangement. The input-output couplers have been designed by using staggered stepped double ridge waveguide, to connect the standard E-band rectangular waveguide and the DS-SDML SWS. An attenuator and pitch tapering have been applied to the proposed SWS to suppress the unwanted frequencies and to improve the output power. Particle-in-cell (PIC) simulation results show that for an 11.8-kV, 200-mA sheet-beam, the output power can reach 283 W at 75 GHz, with a maximum gain and electronic efficiency of 34.5 dB and 11.9%, respectively.

Theoretical and Experimental Study of a Compact Planar Slow-Wave Structure on a Dielectric Substrate for the W-Band Traveling-Wave Tube

A miniature planar meander-type slow-wave structure (SWS) for a W-band traveling-wave tube is studied. Computer simulation of the SWS electrodynamic parameters is performed. A new technology for fabrication of planar microstrip SWSs with the aid of laser ablation is proposed. The S-parameters of the SWS are experimentally studied. The experimental data are in good agreement with the results of the 3D computer simulation. Output characteristics of the traveling-wave tube with a sheet electron beam and planar SWS are calculated.

Теоретическое и экспериментальное исследование миниатюрной планарной замедляющей системы на диэлектрической подложке для лампы бегущей волны W-диапазона

The research results of a miniature meander planar slow-wave structure (SWS) for W-band traveling wave tube are presented. 3D computer simulation of the electrodynamic parameters of SWS has been carried out. A new technology of manufacturing of planar microstrip SWS has been presented. An experimental research of the S-parameters of an SWS has been carried out. The results show good agreement with the results of 3D simulation. The output characteristics of the TWT with sheet electron beam and planar SWS on dielectric substrate were simulated.

Some Advances in Theory and Experiment of High-Frequency Vacuum Electron Devices in China

The advances of high-frequency vacuum electron devices (VEDs) in China are reviewed in this paper, including traveling-wave tubes (TWTs) based on novel slow-wave structures (SWSs), high harmonic TWT amplifier, gyrotrons, Smith-Purcell (SP) radiation sources, surface plasmon polaritons (SPPs) sources, and terahertz (THz) radiation sources in ion-focused beam-plasma system. As one of the most widely used VEDs, TWTs based on folded type SWSs, planar SWSs, and grating type SWSs are studied theoretically and experimentally from Ka-band to R-band. Using folded type SWSs, two TWT amplifiers are developed. As high-power millimeter wave and THz wave sources, gyrotron TWTs, gyrotron oscillators, and gyroklystrons are presented. Moreover, this paper shows SP radiation sources, SPPs sources, and THz radiation sources in ion-focused beam-plasma system open good prospects for developing high-frequency VEDs with new mechanisms, which undoubtedly brings about innovative changes for the development of VEDs.

Analytical treatment of the wakefields driven by transversely shaped beams in a planar slow-wave structure

The suppression of transverse wakefield effects using transversely elliptical drive beams in a planar structure is studied with a simple analytical model that unveils the geometric nature of this phenomenon. By analyzing the suggested model we derive scaling laws for the amplitude of the longitudinal and transverse wake potentials as a function of the Gaussian beam ellipticity - $\sigma_x/a$. We explicitly show that in a wakefield accelerator application it is beneficial to use highly elliptical beams for mitigating transverse forces while maintaining the accelerating field. We consider two scaling strategies: 1) aperture scaling, where we keep a constant charge to have the same accelerating gradient as in a cylindrical structure and 2) charge scaling, where aperture is the same as in the cylindrical structure and charge is increased to match the gradient.

Design of a Microfabricated Planar Slow Wave Structure for a 0.22-THz TWT for Communication, Imaging and Remote Sensing

ABSTRACTA microfabricated planar 0.22 THz TWT is being investigated as a high power, broadband amplifier for ultra-broadband wireless communication, imaging and remote sensing. Planar staggered double-vane-loaded rectangular waveguide slow wave structure (SDV-SWS) is selected for the 0.22 THz TWT because of its wide bandwidth, high impedance and low loss, easy fabrication using MEMS technologies with high precision and surface finish, and inherent compatibility for operation with sheet electron beam. A simplified approach is presented for determining initial design parameters of the SDV-SWS of wide bandwidth and high impedance. The initial design parameters of the SDV-SWS are used for analytically determining the dispersion and the impedance characteristics of the structure which are found comparable with the simulated characteristics by the 3D e.m. field simulator CST code. The SDV-SWS is designed for a planar 0.22 THz TWT with a sheet beam of beam voltage 20 kV and beam current 100 mA. In-house developed large signal analysis code (SUNRAY-p) is used to analyse RF performance of the planar TWT over the band. The RF performance of the 0.22 THz TWT as determined using SUNRAY-p code is found comparable with the simulated results by the CST code over the frequency band.

Experimental demonstration of a terahertz extended interaction oscillator driven by a pseudospark-sourced sheet electron beam

We have recently proposed to combine the advantages of a pseudospark-sourced sheet electron beam (PS-SEB) with a planar slow wave structure to generate high power terahertz radiation. To verify this idea, experimental investigation of an extended interaction oscillator based on the PS-SEB has been conducted and presented. A PS-SEB of approximately 1.0 mm × 0.17 mm in size with 21.5 A peak current (1.26 × 104 A/cm2 beam current density) and 34.5 kV peak voltage was measured after propagating a distance of 10-mm without the need of an external focusing magnetic field. A radiation pulse of ∼35 ns in duration and an output power of over 10 W at a frequency of ∼0.2 THz were measured.

Continuous-wave Y-band planar BWO with wide tunable bandwidth

A high performance continuous-wave (CW) backward wave oscillator (BWO) with planar slow wave structure (SWS) and sheet electron beam in Y-band is presented in this paper. The mode selection is discussed by studying the dispersion curve of SWSs, distributions of the electric field, and particle-in-cell simulation results, showing that the designed BWO operates in the fundamental mode TM11. The planar SWSs are fabricated by using the UV-LIGA technology with the processing error less than 0.003 mm. The electron gun can provide the 2.5 mm × 0.14 mm sheet electron beam with maximum current density of 57 A/cm2 at the CW mode. Experimental results show that the developed BWO can operate in the fundamental mode TM11 and generate the state-of-art output power of 182 mW at the frequency of 0.3426 THz with a large frequency tuning range from 0.318 THz to 0.359 THz.

Dual-frequency low-voltage subterahertz radial clinotron based on fan-shaped splitter

To further improve the output power and tuning bandwidth of compact low-voltage subterahertz vacuum electron devices, a novel dual-frequency low-voltage subterahertz radial clinotron oscillator, in which two fan-shaped radial electron beams transmit inward along the axial direction and interact with two fan-shaped slow wave structures (SWSs) machined on the azimuthally symmetric planar plate individually, is studied in this paper. Compared to the clinotron where the planar SWS composed of the rectangular grooves is adopted, the dispersion curve of proposed fan-shaped radial SWSs is independent of radius and azimuthal coordinates. The particle-in-cell simulation results indicate that the designed clinotron can simultaneously produce the electromagnetic waves at 0.305 THz and 0.34 THz, the corresponding output powers are 9.1 W and 24 W, and the tuning range of bandwidth can be significantly broadened.

$W$ -Band Traveling Wave Tube Amplifier Based on Planar Slow Wave Structure

A novel planar slow wave structure (SWS) for traveling wave tube (TWT) is proposed. The major advantage of the planar architecture is its easy realization with respect to the typical 3-D SWSs. The particle in cell simulations of the TWT show an achievable gain up to 36.4 dB and a maximum output power of 17.4 W for an operating frequency of 92 GHz. The planar structure can be realized using the standard photolithographic techniques, which improve the reproducibility and performance.

Planar slow-wave structures for miniaturized low-voltage Cherenkov devices

Planar slow-wave structures for miniaturized low-voltage Cherenkov devices

Slow-Wave Characteristics of a Frame–Rod Structure Based on Micro-Fabricated Technology for THz Vacuum Electron Devices

A simple equivalent circuit analysis of the frame–rod slow-wave structure (SWS) on dielectric substrates of a traveling-wave tube (TWT) is developed, using the quasi-TEM approximation approach for the dispersion and coupling impedance characteristics of the structure. Moreover, the obtained complex dispersion equation and coupling impedance are numerically calculated. The calculation results by our theory method agree well with the results obtained by the 3D EM simulation software HFSS. It is shown that the dispersion of the frame–rod circuit is decreased; the phase velocity is reduced and the bandwidth becomes greater, while the coupling impedance decreases after filling the dielectric materials in the frame–rod SWS. In addition, a comparison of slow-wave characteristics of this structure with a rectangular helix counterpart is made. As a planar slow-wave structure, this structure has potential applications in compact TWTs based on the micro-fabrication technology, which could be scaled to millimeter wave, even to THz frequency.

Connected Pair of Planar Helices With Straight-Edge Connections for Application in TWTs

A novel planar slow wave structure (SWS) consisting of a connected pair of planar helices with straight-edge connections (PH-SEC) has been proposed in this paper. It is shown with the help of dispersion and coupling impedance characteristics that this structure offers a larger electron-beam tunnel and lower risk of backward-wave oscillation compared with a single PH-SEC. Fabrication using printed-circuit techniques is reported and measured $S$ -parameters over 1–7 GHz are presented to demonstrate the ease of feed-design and wideband characteristics for the new SWS. Using particle-in-cell simulations, hot-test parameters such as the output power, gain, and efficiency are also obtained and reported. It is shown that the connected pair of PH-SECs has a higher gain growth rate than that for the single PH-SEC. The proposed SWS is also compared at frequencies around 60 GHz with a recently reported structure which is derived from meander-line SWS; the comparison shows that the connected pair of PH-SECs offers a significantly higher coupling impedance. With a good potential for fabrication using microfabrication techniques, the connected pair of PH-SECs can be an attractive candidate for application in mm-wave traveling wave tubes.

Planar Helix With Straight-Edge Connections in the Presence of Multilayer Dielectric Substrates

A planar slow-wave structure consisting of a planar helix with straight-edge connections has been studied in the context of application in traveling-wave tubes. The effects of several practical modifications to the basic structure are examined. These modifications comprise a vacuum tunnel, metal shield, and multilayer dielectric substrates. A modified effective dielectric constant method is proposed to obtain the dispersion characteristics for different possible configurations. Furthermore, coupling impedance for the different configurations has been calculated using the corresponding 2-D approximations. It is shown that, far from cutoff, the phase velocity and coupling impedance values calculated in this manner match very well with the simulation results obtained from CST Microwave Studio. The effects of variations in aspect ratio, metal shield distance, and dielectric constant of the substrates on phase velocity and coupling impedance are studied. A coplanar waveguide feed has been designed for one of the possible configurations. The measured S-parameters and phase velocity values for this proof-of-concept configuration agree well with the simulated results and confirm the ease of fabrication, low loss, and the wideband potential of the planar helix with straight-edge connections.

Compact 3-D Envelope ADI-FDTD Algorithm for Simulations of Coherent Radiation Sources

A modified complex-envelope (CE) alternating-direction-implicit (ADI) finite-difference time-domain solver for electromagnetic (EM) fields is presented. Like the conventional ADI scheme, the modified scheme is based on splitting the time step into two halves. In each substep, Maxwell's equations are solved implicitly in one direction and explicitly in the perpendicular direction. The new scheme is a combination of the conventional CE-ADI scheme and the leapfrog ADI scheme that was recently reported. The main features are a more compact form of the tridiagonal equations and greater flexibility in the application of boundary conditions. The boundary conditions on the six faces of the solution box are general and can be specified either as perfect conductor, symmetry boundary conditions, cavity modes, or arbitrary external specification. The new compact CE-ADI scheme is unconditionally stable; thus, the time step can be larger than the one imposed by the Courant-Friedrichs-Lewy (CFL) condition. Fast stable EM simulations of a planar slow-wave structure are demonstrated, with time steps exceeding the CFL limit by two orders of magnitude.

Effective Dielectric Constant Method for a Planar Helix With Straight-Edge Connections

A new planar slow-wave structure consisting of a planar helix with straight-edge connections is presented. It is shown that the phase velocity of the proposed structure can be much slower than that for a rectangular helix with identical cross-sectional dimensions. Further, the dispersion characteristics are obtained simply by using the effective dielectric constant method; it is shown that the method yields results which, far-from-cutoff, match very well with simulation results obtained from CST Microwave Studio. The proposed structure has the potential of easier fabrication using microfabrication techniques.

Radio-Frequency Characteristics of a Printed Rectangular Helix Slow-Wave Structure

A new type of printed rectangular helix slow-wave structure (SWS) is investigated using the field-matching method and the electromagnetic integral equations at the boundaries. The radio-frequency characteristics including the dispersion equation and the coupling impedance for transverse antisymmetric (odd) modes of this structure are analysed. The numerical results agree well with the results obtained by the EM simulation software HFSS. It is shown that the dispersion of the rectangular helix circuit is weakened, the phase velocity is reduced after filling the dielectric materials in the rectangular helix SWS. As a planar slow-wave structure, this structure has potential applications in compact TWTs.