Showing papers by "Yanyu Wei published in 2022"

Broadband-Printed Traveling-Wave Tube Based on a Staggered Rings Microstrip Line Slow-Wave Structure

Abstract: To increase the output power of microstrip line traveling-wave tubes, a staggered rings microstrip line (SRML) slow-wave structure (SWS) based on a U-shaped mender line (U-shaped ML) SWS and a ring-shaped microstrip line (RML) SWS has been proposed in this paper. Compared with U-shaped ML SWS and RML SWS, SRML SWS has a wider transverse width, which means SRML SWS has a larger area for beam–wave interaction. The simulation results show that SRML SWS has a wider bandwidth than U-shaped ML SWS and a lower phase velocity than RML SWS. Input/output couplers, which consist of microstrip probes and transition sections, have been designed to transmit signals from a rectangular waveguide to the SWS; the simulation results present that the designed input/output structure has good transmission characteristics. Particle-in-cell (PIC) simulation results indicate that the SRML TWT has a maximum output of 322 W at 32.5 GHz under a beam voltage of 9.7 kV and a beam current of 380 mA, and the corresponding electronic efficiency is around 8.74%. The output power is over 100 W in the frequency range of 27 GHz to 38 GHz.

Research and Experiment of a W-Band High-Power Extended Interaction Oscillator With High Voltage

Abstract: In order to obtain a high-power radiation source in the W-band, a 95-GHz extended interaction oscillator (EIO) with high voltage was designed and tested in this article. The overall structure of the designed EIO is introduced, and the simulation results of the slow wave structure are shown. Experimental test results show that, at a high duty cycle of 50%, the 95.1-GHz radiation peak power of 3.5 kW is achieved when an electron beam with 2 A and 42.8 kV is injected. The experimental test of the designed EIO has guiding significance for miniaturized vacuum devices to obtain high-power radiation source.

An Approach to Focus the Sheet Electron Beam in the Planar Microstrip Line Slow Wave Structure

Abstract: Planar microstrip line slow wave structures (PML-SWSs) have great prospects in the millimeter and terahertz wave fields. However, the development of the devices employing PML-SWSs is severely limited due to the focusing difficulties. Compared with the conventional sheet electron beam (SEB) SWS, the asymmetric boundary condition of PML-SWS and high local electric field further increase the instabilities of the SEB transport in PML-SWS. A new approach, named the uniform magnetic focusing system with the matching electric field (UMFS-MEF), is presented in this article, which can effectively solve these issues. The simulation results illustrate that the expansion rate of the SEB in UMFS-MEF is significantly lower than that in the conventional uniform magnetic focusing system (CUMFS) with the same magnetic field strength ${B}_{z}$ . Moreover, the present calculation results show that the UMFS-MEF requires only 10.6% of the magnetic field strength of CUMFS for maintaining the same expansion rate. This means that the UMFS-MEF can effectively suppress the instabilities, and employ a very low magnetic field to maintain the stabilities of the SEB transport. Finally, we give several other schemes to realize the method.

Rectangular Grating Slow-Wave Structure With a Slot Embed Electron Beam for High-Power Terahertz Radiation

Abstract: To enhance the output power of 0.5-Terahertz (THz) backward wave oscillator (BWO), a grating loaded rectangular waveguide (GLRW) slow-wave structure (SWS) with a slot embed electron beam (SEEB) is proposed in present work. For the designs and optimizations of BWO GLRW SWS with SEEB, the dispersion equations are derived with a field matching method (FMM) and solved by a numerical method; the results show that the coupling impedances are remarkably enhanced. Moreover, the output performances are studied with a help of particle-in-cell (PIC) simulation, and the simulated results show that the BWO operation voltage is 25 kV and the current is 40 mA; the output power 18.9 W of the perfect electronic conductor SWS with SEEB is obtained, which is improved about 1.5 times. On the other hand, the time of start oscillation is decreased to 50%, which is compared with that the conventional SWS without slot. As for the THz vacuum electronic devices (VED), the amplitudes of output power are remarkably affected by the conductivity and roughness of SWS; therefore, the determinate factors are studied, and the PIC results show that the maximum power is about 5–7 W when the conductivity is 3– $5\times10$ 7 S/m. The proposed scheme affords a promising option for the developing of high-power THz source.

Experimental Investigations on Effects of Operation Parameters on a 263-GHz Gyrotron

Abstract: In this article, the experimental investigations on a 263-GHz gyrotron are presented. With the change of the operating magnetic field and the beam energy, the operating frequency is adjusted and the output power is also varied. It is found that when the operating magnetic field changes from 9.59 to 9.82 T at a fixed operating voltage of 20 kV and a beam current of 0.8 A, the operating frequency increases from 263.39 to 264.84 GHz, the frequency-tuning range is about 1.45 GHz, and the output power is from 26 to 463 W. When the operating voltage increases from 14.4 to 22.2 kV at a fixed operating magnetic field of 9.65 T, the operating frequency decreases from 263.68 to 263.40 GHz, the frequency-tuning range is 0.28 GHz, and the output power changes from 52 to 424 W. When the operating magnetic field is fixed at 9.65 T and the operating voltage is fixed at 20 kV, but the beam current increases from 120 to 880 mA, the output power increases from 21 to 277 W, the operating frequency increases from 263.396 to 263.425 GHz, and the frequency-tunable range is 0.029 GHz. The effects of the axial position of the gyrotron in the superconducting magnet system on the operating frequency, the frequency-tuning range, and the output power are also investigated experimentally. When the beam current is increased, the nonstationary phenomenon is observed.

A piecewise sine waveguide for terahertz traveling wave tube

Abstract: Abstract In this paper, a piecewise sine waveguide (PWSWG) is proposed as the slow-wave structure (SWS) to develop high-power terahertz (THz) traveling wave tubes (TWTs). The PWSWG is an improvement over the rectangular waveguide wherein its two E-planes simultaneously oscillate up and down along the longitudinal direction. The oscillation curve in the H-plane is a piecewise sine curve formed by inserting line segments into the peaks and troughs of the sine curve. The simulation analysis and experimental verification show that the PWSWG offers the advantages of large interaction impedance and excellent electromagnetic transmission performance. Furthermore, the calculation results of beam–wave interaction show that the TWT based on PWSWG SWS can generate a radiated power of 253.1 W at the typical frequency of 220 GHz, corresponding to a gain of 37.04 dB and an interaction efficiency of 6.92%. Compared with the conventional SWG TWTs, the PWSWG TWT has higher interaction efficiency and shorter saturation tube length. In conclusion, the PWSWG proposed in this paper can be considered a suitable SWS for high-power THz radiation sources.

Design and Simulation for 100-Watt-Class 340-GHz Extended Interaction Klystron

Abstract: An extended interaction klystron (EIK) working at the frequency of 340 GHz is designed in this present article. The characteristic impedance, coupling coefficient, and normalized electron conductance of the cold cavities are analyzed and optimized. To improve the output power, the EIK adopts a prebunching (PB)-cavity high-frequency structure (HFS). Compared with the conventional terahertz (THz) EIK, the coherence of PB-cavity EIK is enhanced, and the output power is improved. The 3-D particle-in-cell (PIC) simulation predicts the EIK, driven by a 0.20-A, 22.4-kV electron beam confined in a 0.2-mm-diameter beam tunnel, and generates an output power of 138.3 W at the frequency of 339.7 GHz. The gain, electronic efficiency, and 3-dB bandwidth are 39.6 dB, 3.1%, and 500 MHz, respectively. The proposed EIK can be applied to the THz high-resolution radar.

Detailed Investigation on Nonstationary Behavior in a Frequency-Tunable Gyrotron

Abstract: As a terahertz (THz) radiation source, the frequency-tunable gyrotron is promising in application and attractive to researchers. In this article, the nonstationary phenomenon in a frequency-tunable gyrotron operating in different regimes—gyromonotron, transition, and gyro-backward-wave oscillator (BWO)—has been investigated in detail by 3-D particle in cell (PIC) simulation. Simulated results demonstrate that among the three regimes, gyromonotron has the strongest capability to keep stationary, and nonstationary oscillations are most likely to occur in the transition regime. Moreover, in the gyro-BWO regime, the capability of the system to maintain steady-state operation gets slightly improved with the increase in the axial mode. The corresponding interpretation is based on detuning frequency and feedback mechanism. Finally, the effect of the velocity spread on the nonstationary behavior has also been studied. Investigations reveal that the stability of stationary oscillations would be weakened when velocity spread is considered. The results in this article may be of benefit of a deeper insight into the nonstationary phenomenon in a frequency-tunable gyrotron.

Attempt on Applying Semi-Metallic Supporting Rods to a Wideband Ka-Band Helix TWT

Abstract: A helix traveling-wave tube (TWT) with semi-metallic rods operating at 26.5–40 GHz is presented. Its promising feature is to provide wide-bandwidth interaction with a compact structure, low gain fluctuation, adequate output power, and electronic efficiency. Such rods may easily transfer the heat out of the helix circuit compared with the conventional helix SWS. Thermal simulation shows that the maximum temperature of this helix structure can be 40 °C–56 °C cooler than the helix slow-wave structure (SWS) with anisotropic boron nitride (APBN) rods under the same heat loads. Moreover, the deformation of the helix with the semi-metallic rods due to heat conduction is at least 33% smaller than that of the helix with all-APBN rods. The electromagnetic characteristics and the beam-wave interaction based on this SWS are investigated and optimized. The calculation results predict that it potentially could provide saturated output power over 180 W from 26 to 40 GHz when the cathode voltage is 9000 V and beam current is 140 mA, respectively. The corresponding saturated gain and electron efficiency can reach over 43.3 dB and 14.6%, and the gain fluctuation is only about 6–7 dB. Furthermore, the fabrication methods of the semi-metallic rods are explored carefully. The transmission characteristics of the designed helix TWT with semi-metallic rods are experimentally validated by a cold test, showing the voltage standing wave ratio (VSWR) of the high-frequency structure is below 1.98 in the range of 26 to 40 GHz.

Investigation and Fabrication of the Printed Microstrip Meander-Line Slow-Wave Structures for D-Band Traveling Wave Tubes

Abstract: Two typical topology shapes of the microstrip meander line (MML) including round U-shaped and V-shaped slow-wave structure (SWS) for ${D}$ -band traveling wave tubes (TWTs) are comparatively investigated, fabricated, and tested in this article. As a critical factor applied in millimeter-wave frequency, the high-frequency losses of the MML SWS are emphatically discussed. The two types of golden SWSs are both fabricated with the thin-film circuit technology on quartz substrates. After the surface roughness test and the cavity fabrication, the SWS samples are assembled and tested. According to the experimental test results, the ${S}_{11}$ parameters of the U-shaped and V-shaped transmission models are below −13.5 dB versus −15 dB, and the “cold” ${S}_{21}$ parameters are over −6.4 dB versus −4.9 dB, which are approached to the simulation results with the consideration of the silver conductive paste (SCP). At 140 GHz, the tested transmission losses for the U-shaped SWS and V-shaped SWS are about 0.35 and 0.29 dB/mm, respectively. Although particle-in-cell (PIC) simulations for the two SWSs both predict more than 100-W output power, the V-shaped MML TWT shows better bandwidth and loss performances than the U-shaped MML TWT.

Accurate Local Modulation of Graphene Terahertz Metamaterials by Direct Electron Beam Irradiation

Abstract: Electrical gating has been typically used for Graphene-based devices to deliver high performance with superior electrical controllability. In this study, we utilize direct electron beam irradiation to attain the electrical controllability of graphene. The newly established system combines terahertz time-domain spectroscopy (TDS) with scanning electron microscopy (SEM). We experimentally demonstrate the precise localized tuning of graphene terahertz metamaterials, as the size and position of the electron beam generated by SEM are highly controllable. Furthermore, graphene metamaterials with different chemical potentials are simulated, and the results are highly consistent with the experiments.

A High Interaction Impedance Microstrip Meander-Line With Conformal Dielectric Substrate Layer for a W-Band Traveling-Wave Tube

Abstract: A U-shaped microstrip meander-line (MML) with an additional conformal dielectric substrate layer (CMML) is investigated for application in ${W}$ -band traveling-wave tubes (TWTs). The interaction impedance of such slow wave structure (SWS) is at least 29% higher than that of typical N-shaped and U-shaped MML circuits with the same dimensions. Furthermore, the conformal substrate layer probably results in less energy concentration in the dielectric substrate to reduce attenuation and also reduces the chance of electron striking and accumulation on the substrate. In addition, a customized waveguide housing with input–output coupler is optimized for the relatively wider substrate width to house the SWSs and facilitate measurements. The particle-in-cell (PIC) simulation results predict that it potentially could provide maximum saturated output power 31.4 W and 21.9 dB gain at 96 GHz, with a 3-dB bandwidth of 92–98 GHz when the operating voltage is 6550 V and beam current is 100 mA, respectively. If the thickness of conformal quartz layer increases to $30 ~\mu \text{m}$ , the maximum output power can reach over 80 W. The measured S-parameters of the proposed entire 20-period structure match the simulated one well. The measured ${S}_{21}$ is better than −5.3 dB in the frequency range of 88–102 GHz. Attenuation is about 5.9–7.7 dB/cm in the ${W}$ -band, which is better than the measured results reported before.

Research Progress of G-band Continuous Wave Backward Wave Tube

Abstract: Based on sheet electron beam, grating slow wave structure and clinotron backward wave tube technology, G-band 30 mW continuous wave backward wave tube has been successfully developed. By introducing a centralized attenuator, the self-excited oscillation caused by reflection is eliminated. The output power of the device is greater than 30 mW in the whole frequency range of 250 GHz~300 GHz.

An Efficiency-Enhanced 0.5-THz BWO Using Double-Slot Embedded Electron Beams to Drive a Grating Loaded Rectangular Waveguide

Abstract: The backward wave oscillator (BWO) is one of the best choices for generating high-power radiation waves in the terahertz (THz) region. In order to improve the efficiency of beam–wave interaction and output power, a novel THz BWO scheme is proposed in this article, which uses double-slot embedded electron beams (DSEEB) to drive a grating loaded rectangular waveguide (GLRW) slow wave structure (SWS). The dispersion relation and the coupling impedance of the proposed SWS are derived by using an eigenfunction method (EFM) and solved with a numerical method. The results show that the upper limit frequency and the coupling impedances are remarkably improved, which are greater than those of traditional grating SWS. Based on this scheme, a BWO operating at the frequency of 0.5 THz is designed. The particle-in-cell simulations show that the output power reaches 8.86 W with an efficiency of 0.9%, which is 2.5 times the electronic efficiency of the conventional BWO. Thus, the proposed scheme provides a promising aim to develop the high-power THz source, which may be used in THz biomedical and material studies, and so on.

Design of a 4-kW 27-31-GHz Traveling Wave Tube Based on Sine Waveguide

Abstract: A Ka-band sheet beam high power traveling wave tube based upon sine waveguide slow wave structure is studied. In this paper, phase velocity tapering technology is applied to improve electronic efficiency. The simulation result of beam wave interaction turns out that the output power is higher than 4000 W and the gain is more than 23 dB ranging from 27 GHz to 31 GHz with synchronous voltage of 29.1 kV and operation current of 800 mA.

Investigation of a Modified Flat-Roofed Sine Waveguide Slow-Wave Structure for Wideband 220-GHz TWT

Abstract: In this letter, the modified flat-roofed sine waveguide slow-wave structure (FRSWG-SWS) is proposed for the wideband high-power sub-terahertz traveling-wave tube (sub-THz TWT), which possesses the advantages of wide operating bandwidth, low loss, minimal reflection, and ease of fabrication. The simulation results demonstrate that the transmission parameter is more than −5.0 dB in the frequency range between 210 and 250 GHz. The beam–wave interaction results indicate that the modified FRSWG can provide over 50 W of output power and 30 dB of gain from 205 to 250 GHz with sheet electron beam with a voltage of 20.8 kV and a current of 150 mA. Finally, we use high-speed milling to fabricate the modified FRSWG by the nano-Computer Numerical Control (CNC) technology. The cold test results demonstrate that the modified FRSWG has low loss and good reflection characteristics.

Investigation of Half Rectangular-Ring Helix Slow Wave Structure for W-Band Wide Bandwidth High-Efficiency TWTs

Abstract: The half rectangular-ring helix (HRRH) slow wave structure (SWS), which evolves from the rectangular helix (RH), is proposed to develop a high-efficiency wide bandwidth millimeter-wave traveling-wave tube (TWT). The comprehensive advantages of the HRRH SWS are lower phase velocity and higher interaction impedance in comparison with the RH and the planar helix with straight-edge connections (PH-SECs) SWS with the same dimensions. The particle-in-cell (PIC) simulation shows that, at a beam voltage of 6450 V, a beam current of 0.03 A, the maximum output power of 42.2 W, corresponding to a differential small-signal gain of 1.43 dB/mm, and an electron efficiency of 21.8% can be obtained for the HRRH TWT at 95 GHz. The output power, differential small-signal gain, and electron efficiency of the HRRH TWT are considerably enhanced compared with the RH TWT in a wide frequency range of 60–115 GHz under the same electrical parameters.

Theoretical and Experimental Investigations on Input Couplers for a Double Confocal Gyro-Amplifier

Abstract: Two types of double confocal waveguide ${\mathrm {TE}}_{06}^{anti} $ -mode input couplers operating at 140 and 220 GHz are theoretically and experimentally investigated in this article, respectively. The 140 GHz input coupler is based on a power division network structure, while the 220 GHz input coupler is based on a coaxial resonant cavity structure. The field pattern of these two input couplers are analyzed and discussed. The prototypes were fabricated and tested. Back-to-back transmission experimental results agree well with the results of the theoretical simulations. The experimental results show that the 3 dB bandwidth of the power division input coupler at 140 GHz is about 9 GHz and the maximum transmission is −1.4 dB. The 3 dB bandwidth of the coaxial cavity input coupler at 220 GHz is about 3.5 GHz and the maximum transmission is −0.9 dB. It means that a wider bandwidth can be obtained from the power division input coupler, while a higher conversion efficiency can be obtained fromthe coaxial cavity input coupler. The proposed methodology can be applied to the design of an arbitrary ${\mathrm {TE}}_{0{n}}^{\text{anti}} $ ( ${n} >=2$ ) mode input coupler for a double confocal structure gyro-amplifier.

Bandwidth enhancement for over-mode traveling-wave amplifiers

Abstract: To increase the bandwidth of conventional over-mode traveling wave tubes (TWTs) with single-mode existing (SME) in an operation band, a theory on over-mode TWTs with multi-modes coexisting (MME) in the operation band is presented in this paper. To verify this theory, G-band dual-beam and shunted coupled Hughes-type coupled-cavity TWTs with MME and SME are investigated. The particle-in-cell simulation analysis confirms that, compared with SME TWT, the MME TWT can not only operate stably but also has 2.24 times bandwidth and a large increase in the output power.

Accurate modulation of graphene metamaterials with no-electrode through free electrons

Abstract: 2D material graphene has a wide range of applications in terahertz, most graphene modulation is performed with electrodes for gate voltage modulation or high-power laser pulse modulation. Here, we construct a self-developed system based on scanning electron microscopy (SEM) combined with terahertz time-domain spectroscopy (TDS) to experimentally demonstrate the tuning of a no-electrode graphene metamaterial modulation. Because the electron beam radius and position of the SEM is highly controllable, it can be adjusted precisely. This is of seminal importance for the development of terahertz graphene terahertz devices.

Study on a Novel Dual-Beam Flat-Roofed Sine Waveguide Traveling-Wave Tube

Abstract: The present study develops a dual-beam flat-roofed sine waveguide slow wave structure (SWG SWS) by complying with the conventional flat-roofed SWG SWS in this article. Through the placement of a metal plate in the electron beam tunnel center of conventional flat-roofed SWG SWS, the electron beam tunnel is divided into two tunnels. The SWS exhibits a wide working bandwidth, low loss, and small reflection by optimizing the structural size of the dual-beam flat-roofed SWG. Moreover, a comparison is drawn of the slow wave characteristics and beam–wave interaction between dual-beam flat-roofed SWG and conventional flat-roofed SWG. As revealed from the results, the output power level of the dual-beam flat-roofed SWG traveling-wave tube (TWT) is significantly higher than that of the flat-roofed SWG TWT exhibiting the identical current density or the input power. Furthermore, this study develops a $W$ -band high-gain dual-beam flat-roofed SWG TWT with an attenuator. The maximum output power is 756.6 W at 93 GHz, and the corresponding gain is 38.73 dB. In the frequency range of 89–100 GHz, the output power reaches over 500 W, and the 3-dB bandwidth exceeds 10 GHz.