Hairong Yin

A Novel V-Shaped Microstrip Meander-Line Slow-Wave Structure for W-band MMPM

In this paper, a novel V-shaped microstrip meander-line slow-wave structure (SWS) is proposed for use in a low-voltage high-efficiency wide-bandwidth miniature millimeter-wave traveling-wave tube (TWT). The electromagnetic characteristics and the interaction between the sheet electron beam and slow wave in this SWS are obtained by utilizing the CST Microwave Studio and Particle Studio codes, respectively. From our calculations, it is predicted that, at a beam voltage of 3.7 kV and a beam current of 100 mA, an output power greater than 30 W can be obtained ranging from 75 to 100 GHz, and this V-shaped microstrip meander-line TWT will be helpful for a W-band millimeter-wave power module.

A watt-class 1-THz backward-wave oscillator based on sine waveguide

A novel backward wave oscillator was proposed by utilizing a concise sine waveguide slow-wave structure combined with sheet electron beam to operate at terahertz frequency band. First, the design method was described, and the dispersion curve and interaction impedance of the sine waveguide were calculated, then the device oscillation frequency and operating voltage were determined. Next, the circuit transmission losses were learned over the tunable frequency range. Finally, the particle-in-cell simulation method was applied to predict its signal generation performance. The investigation results show that, the backward wave oscillator can produce over 1.9 -W peak power output at the central operating frequency of 1-THz under 27-kV operating voltage and 5-mA beam current. And the interaction efficiency at 1-THz is more than 1.4% with a circuit length of 7.2-mm. It, therefore, will be considered as a promising watt-class terahertz radiation source.

Sine Waveguide for 0.22-THz Traveling-Wave Tube

A novel slow-wave structure called sine waveguide has been proposed to develop a wideband high-power terahertz radiation source. The sine waveguide evolves from a rectangular waveguide oscillating with sinusoid along its longitudinal direction. This letter reports the electromagnetic characteristics of the sine waveguide and its effective surface plasmon amplification mechanism. From our calculation, this circuit structure possesses low ohmic losses and reflection and can be applied to produce terahertz waves ranging from 0.2 to 0.25 THz with several hundreds of watts. Moreover, the maximum gain and interaction efficiency may reach 37.7 dB and 9.6%, respectively.

High-Power Millimeter-Wave BWO Driven by Sheet Electron Beam

The sheet beam vacuum electron device is an attractive choice for generating high-power high-frequency microwave radiation. A millimeter-wave sheet beam backward wave oscillator (BWO) is presented in this paper. The rectangular waveguide grating structure is used as its slow wave structure. The BWO is driven by a sheet beam with a cross-sectional area of 30 mm × 1 mm which is generated by a thin cathode. For a beam voltage of 167 kV and a beam current of 1.4 kA, the output power is 40 MW at 36.6 GHz. The beam-wave interaction efficiency is about 17%, which is higher than that of conventional hollow beam BWO. It is clear from the results presented in this paper that the sheet beam device is promising for producing high-efficiency high-power millimeter-wave radiation.

A 140-GHz Two-Beam Overmoded Folded-Waveguide Traveling-Wave Tube

A folded-waveguide (FW) traveling-wave tube (TWT) with two electron beams, which operates at the higher order mode, is simulated. Operating with two electron beams means that a larger beam current can be used for a higher output power. Meanwhile, the electric field density of the fundamental mode is not the strongest at the center of the beam channel, so the competition of the fundamental mode is significantly suppressed. A four-section two-beam FWTWT at 140 GHz is designed to get 100 W of average power. From the simulation results, we can see that this kind of tube is unstable if the gain per section is over 11 dB, because both fundamental and band-edge modes are strongly excited. Then, another way for a stable FWTWT operation with two electron beams by loading with dielectric is also presented in this paper. The results presented here can provide a new way to obtain high power radiation at the terahertz frequency.

Stable Sheet-Beam Transport in Periodic Nonsymmetric Quadrupole Field

Stable sheet electron-beam transport is critical for sheet-beam microwave device which is attractive for high-power millimeter wave to terahertz-regime radiation. This paper studies the stable sheet-beam transport in periodic nonsymmetric quadrupole field. First, the conditions for stable round- and sheet-beam transport in periodic magnetic quadrupole field are deduced. In the deduction, we find that the symmetric quadrupole field and the space-charge field of sheet beam are not well matched. In order to settle this problem, we use periodic nonsymmetric quadrupole field instead of periodic symmetric quadrupole field to transport sheet beam. Finally, 3-D PIC simulations verify the conditions for stable sheet-beam transport and show that periodic nonsymmetric quadrupole field is intrinsically well suited for sheet-beam transport.

Study of Traveling Wave Tube With Folded-Waveguide Circuit Shielded by Photonic Crystals

The design and simulated performance of a traveling-wave tube (TWT) constructed by combining a folded-waveguide (FW) slow-wave circuit with arrays of 2-D photonic crystals (PhC) are presented. Numerical results reveal that the Pierce interaction impedance of the FW circuit with PhCs is similar to the circuit without PhC arrays. The gain, output power, and efficiency of TWTs with and without PhCs are also similar when the circuit dimensions are identical; however, the TWT with PhCs can filter out nonoperating modes, which may improve the stability of the circuit shielded with PhCs when compared to the same circuit shielded by metal walls.

140-GHz V-Shaped Microstrip Meander-Line Traveling Wave Tube

A study on a miniature, low voltage, wide bandwidth, and high RF efficiency V-shaped microstrip meander-line slow-wave structure is carried out in this paper. The fabrication of this structure is very convenient by utilizing the 2-D micro-fabrication techniques. Radio-frequency characteristics including dispersion properties, interaction impedance and S-parameters are analyzed. Based on these results, nonlinear large signal performances of the V-shaped microstrip meander-line traveling-wave tube are calculated by 3-D particle-in-cell code. This study shows that this miniature millimeter-wave power amplifier is capable of delivering several tens of watts output power ranging from 127 GHz to 145 GHz.

Novel Folded Frame Slow-Wave Structure for Millimeter-Wave Traveling-Wave Tube

A new type of folded frame slow-wave structure (SWS) is introduced and used in the design of a low-voltage, high-efficiency, and widebandwidth millimeter-wave traveling-wave tube (TWT). The high-frequency characteristics of the folded frame structure, including dispersion properties, coupling impedances, and reflection characteristics are investigated. The beam-wave interaction of the TWT with the folded frame SWS working at the millimeter-wave frequency range is also calculated using 3-D particle-in-cell algorithms. The simulation results reveal that with sheet electron beam parameters of 6000 V and 0.2 A, the average output power and electron efficiency can reach 196 W and 16.3%, respectively. Compared with the symmetric double V-shaped microstrip meander-line SWS, the folded frame SWS has larger coupling impedances and can generate higher output power.

EQUIVALENT CIRCUIT ANALYSIS OF RIDGE-LOADED FOLDED-WAVEGUIDE SLOW-WAVE STRUCTURES FOR MILLIMETER-WAVE TRAVELING-WAVE TUBES

In this paper, a new simple equivalent circuit model for analysis of dispersion and interaction impedance characteristics of ridge-loaded folded-waveguide slow-wave structure is presented. In order to make the computational results more accurately, the efiects of the presence of the beam-hole and discontinuity due to the waveguide bend and the narrow side dimension change of this kind of structure were considered. The dispersion characteristics and the interaction impedance are numerical calculated and discussed. The analytical results agree very well with those obtained by the 3-D electromagnetic high-frequency simulation software. It is indicated that the equivalent circuit methods are reliable and high e-ciency.