Showing papers by "Yanyu Wei published in 2019"

Terahertz Radiation from Combined Metallic Slit Arrays.

Abstract: We report an approach to efficiently generate terahertz radiation from a combined periodic structure. The proposed configuration is composed of two metallic slit arrays deliberately designed with different periodic length, slit width and depth. We found that the combination of the two slit arrays could provide special electromagnetic modes, which exhibit nonradiative property above the surface of one slit array and radiative property inside the other one. An electron beam holding proper energy could resonate with those modes to generate strong and directional electromagnetic radiations in the terahertz regime, indicating that the approach has the potential in developing high-performance terahertz radiation sources.

Experimental Verification of the Low Transmission Loss of a Flat-Roofed Sine Waveguide Slow-Wave Structure

Abstract: The sine waveguide (SWG) is presented as a potential slow-wave structure (SWS) for the millimeter-wave (mm-wave) and terahertz (THz) traveling-wave tube (TWT) because of the advantages of wide bandwidth, natural electron beam tunnel, and easy fabrication. In particular, this theoretical study indicates that the transmission loss of the SWG is far less than that of the folded waveguide SWS, which is widely employed in the mm-wave and THz TWT. Here, the flat-roofed SWG slow-wave circuit working in the ${W}$ -band has been machined using nano-computer numerical control technology, which guarantees micron tolerances and surface roughness of tens of nanometers using carbide tooling with 100- ${\mu }\text{m}$ diameter. The cold test results show that the transmission coefficient ${S}_{{{21}}}$ of the entire high-frequency slow-wave circuit is more than −4.1 dB with a total length of 123.84 mm in the frequency range from 90 to 100 GHz, and the transmission loss is less than 0.36 dB/cm.

Study of 220 GHz Dual-Beam Overmoded Photonic Crystal-Loaded Folded Waveguide TWT

Abstract: This paper puts forward a novel dual-beam overmoded folded waveguide (FW) slow-wave structure (SWS), which is loaded with photonic crystals. In this novel structure, the two electron beams pass through the small gaps between the photonic crystal structures and the FW; the dimension of the FW is twice larger than that of the fundamental mode structure. The novel dual-beam photonic crystal overmoded FW traveling-wave tube (TWT) is proposed on the basis of the SWS. And, a mode converter is introduced to achieve the connection between the SWS and the input/output structure, and the mode transformation. At the operating voltage of 21.2 kV and the operating current of 320 mA, the proposed TWT can generate 128 W of output power at 220 GHz, and its 3-dB bandwidth is 7 GHz, ranging from 216 to 223 GHz.

Stacked dual beam electron optical system for THz integrated wideband traveling wave tube

Abstract: In this paper, a stacked dual beam electron gun and the associated electron optical system are proposed. The stacked dual beam electron gun includes two compact focusing electrodes which help to achieve dual sheet beams. As an application of this dual beam electron gun, a 340 GHz integrated dual beam traveling wave tube (TWT) based on the staggered dual vane slow-wave structure (SWS) is also put forward. In order to reduce the length of the TWT, a novel input/output coupler is introduced. The overall transmission characteristics of the SWS structure together with the input/output couplers show a wide bandwidth covering a frequency range of 306 GHz to 360 GHz. Based on the parameters obtained for the integrated TWT, a stacked dual-beam electron gun with dual focusing electrodes is designed to achieve a beam current of 43 mA, a beam voltage of 21.4 kV, and a cross-sectional size of each beam of 0.3 mm × 0.08 mm. A uniform magnetic field of 0.52 T is utilized to focus the dual electron beams, and a beam transmission efficiency of 97.1% is achieved over a length of 50 mm. Finally, particle in cell simulation results show that the integrated dual-beam TWT can generate an output power of 5 W over the frequency range of 315 GHz to 350 GHz, with the maximum output power of 24.5 W at 330 GHz.

3-D Fast Nonlinear Simulation for Beam–Wave Interaction of Sheet Beam Traveling-Wave Tube

Abstract: In this paper, a 3-D fast time-domain nonlinear algorithm (FTDNA-3-D) based on particle-in-cell method for the beam–wave interaction of the sheet beam slow wave structure (SWS) is presented. Calculation equations of the circuit electric field and the space charge electric field are given. Calculation approaches of the energy exchange and the particle mover are displayed. A simplified coupling impedance simulation approach for sheet beam SWS is indicated. The FTDNA-3-D takes the transverse electric field and the focusing magnetic field into consideration. The FTDNA-3-D could reach a high simulation speed. This novel algorithm gives a faster accurate choice for the design of sheet beam traveling-wave tube (TWT). It could be used to enhance the design efficiency of sheet beam TWT. A Ka-band staggered double vane TWT is used to verify the FTDNA-3-D. Simulation results of output power and gain versus frequency from FTDNA-3-D are compared with results from CST particle studio. The results of FTDNA-3-D are in accord with CST particle studio well.

Study of low voltage angular log-periodic slow wave structure for 340 GHz TWT

Abstract: A novel angular log-periodic groove waveguide slow wave structure (SWS) for 340 GHz traveling wave tube (TWT) is proposed in this paper. Due to the unique characteristics of log-periodic form, the novel SWS could achieve a very low operating voltage and small scale at the same time. By using the groove folded waveguide, the high aspect ratio fan-shaped sheet electron beam could interact with electromagnetic wave in the groove tunnel. According to direct mathematical equation, the operating voltage is 6310 V at 340 GHz and the total length of SWS is 8.6 mm, which could get an output power of 36 W with 20.7 dB gain.

Study of Sheet Beam Electron Optical System and Energy Coupler for Wideband 340GHz TWT

Abstract: An electron optical system with long-range low emission current density electron gun and H-plane double-slit coupling input-output RF coupler are studied for 340GHz sheet beam staggered double vane traveling wave tube (TWT). The long-range sheet beam electron gun can reduce the difficulties in assembling and adjusting of the whole magnetic system. Low emission current density can reduce the processing difficulty and improve the life of the electron gun. The bandwidth of the microwave circuits with H-plane double-slit input and output couplers is so broad that can approach 45GHz. Taking the high frequency loss of copper into account, the beam-wave interaction simulation shows that the whole design provides 14.6W of output power and 31.6dB gain at 340GHz.

One-dimensional nonlinear analysis of sine waveguide traveling-wave tubes

Abstract: A 1D frequency-domain nonlinear model for illustrating the beam-wave interactions of sine waveguide (SWG) traveling-wave tubes (TWTs) was studied. Our model considered space-charge fields and Ohmic losses to make the model closer to practical situations. The sheet beam was split into a series of rectangular electron plates in the axial direction, and the space-charge field was calculated by solving Green's function. The dynamic equations and relativistic equations of motion were solved self-consistently to obtain the nonlinear characteristics of the power saturation, as well as the electron velocity, phase space distributions, etc. A 0.22 THz SWG TWT was used to illustrate and verify the validity of the theoretical model. The output power and gain results were in good agreement with those from the Computer Simulation Technology (CST) 3D particle-in-cell simulation. In addition, the code developed based upon the theoretical model produced faster results than the CST simulation.

Design of a Sheet Beam Electron Gun for 850GHz Staggered Double Vane Traveling Wave Tube

Abstract: A sheet beam electron gun for 850GHz staggered double vane TWT is designed in this paper. The designed beam achieves a beam current of 20mA, beam voltage of 28.1kV and cross-sectional dimension of $\pmb{0.12}\mathbf{mm}\pmb{\times 0.03}\mathbf{mm}$ . And the beam transmission efficiency with a designed uniform permanent magnetic field is achieved with 95.7%. Finally the beam-wave interaction with above parameters is calculated and the output power is obtained with 33.8mW.

Design of a quasi flat-roofed sine waveguide Slow-wave structure for 220GHz TWT

Abstract: A novel quasi flat-roofed sine waveguide slow wave structure (SWS) is presented for the wideband high-power terahertz traveling-wave tube (TWT). The quasi flat-roofed sine waveguide SWS (QFRSWG TWT) possesses the similar slow-wave characteristics with the flat-roofed sine waveguide SWS in the frequency range of 0.2-0.26THz. The beam-wave interaction results indicate that the TWT based upon this QFRSWG can generate the output power of 136W at 220GHz by using the sheet electron beam of 20.8kV and 100mA.

A Way to Match the Second Symmetric Mode of Double-Grid Slow Wave Structure for Terahertz BWO

Abstract: In this paper, a way to match the second symmetric mode of double-grid slow wave structure designed for a practical 1-THz terahertz backward wave oscillator is presented. Simulation results show that the return loss is less than -15 dB, and the insertion loss is about -4 dB in the 50-GHz operating bandwidth.

Design of a W-band traveling-wave tube based on sine waveguide slow-wave structure with sheet electron beam

Abstract: A W-band TWT based upon flat-roofed sine waveguide slow-wave structure is designed. The transmission characteristics of high frequency structure with input/output window show that the $\mathbf{S}_{\pmb{2}}$ 1 is more than −4 dB and $\mathbf{S}_{\pmb{11}}$ is less than −16 dB. The beam-wave interaction results show that the output power is more than 40 W range from 90 GHz to 100 GHz with voltage of 19 kV and current density of 50 mA/cm2.

Multiphysics analysis of Ka-band U-shaped microstrip line planar traveling wave tube

Abstract: In this paper, multiphysics field simulation is applied to analyze the temperature distribution of Ka-band U-shaped microstrip line planar TWT considering the thermal losses induced by ohmic loss and electron collision losses. The beam-wave interaction of the planar TWT is analyzed by using CST particle-in-cell (PIC) solver, at the same time the thermal losses distribution is recorded, which will be the heat source. The simulation results show that the high temperature with a peak value of 263 °C.

220GHz Sine Waveguide BWO with large Beam Tunnel

Abstract: The development of 220GHz sine waveguide BWO with cylindrical beam tunnel is presented here. The particle-in-cell (PIC) simulation result predicts that this device can product the output power over 6.SW in frequency range of 214.07GHz to 224.99GHz. The radius of beam tunnel is 0.2 mm. The beam current is chosen as 70mA which has a current density of 99A/cmA2. The uniform magnetic is 0.25T.

Interaction Impedance Measuring Method in Sine Waveguide

Abstract: The sine waveguide has been proved to be a promising structure with excellent transmission characteristics. In this work, a formula measuring the interaction impedance for sine waveguide is given based on the non-resonant perturbation theory. The measuring results of diversion characteristic and interaction impedance are compared with the simulation results for a sine waveguide slow-wave structure operating in W-band and the differences between the two results are less than 3.5% and 11.2%.