Lingna Yue

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.

A Novel Ridge-Vane-Loaded Folded-Waveguide Slow-Wave Structure for 0.22-THz Traveling-Wave Tube

A novel slow-wave structure called ridge-vane-loaded folded waveguide combined with pencil electron beam has been proposed for millimeter-wave traveling-wave tubes. The high-frequency characteristics including the dispersion properties and the interaction impedance of this kind of structure have been analyzed by means of an equivalent circuit based on the transmission-line cascading network. The theoretical results agree well with those obtained by the 3-D electromagnetic high-frequency simulation software. The nonlinear interaction between the electron beam and the electromagnetic field is investigated with the help of the Computer Simulation Technology Particle Studio 3-D particle-in-cell (PIC) code. The PIC simulation results revealed that this kind of structure could produce about 56 W of peak output power at 0.22-THz when the cathode voltage and current of the pencil electron beam are set to 14.65 kV and 50 mA, respectively. Moreover, the maximum gain and interaction efficiency can reach 37.5 dB and 7.7% at 0.22 THz, respectively. A simulated 3-dB bandwidth of ~ 30 GHz is demonstrated.

Study of Corrugated Elliptical Waveguides for Slow-Wave Structures

The slow-wave characteristics taking account of space harmonics for confocal corrugated elliptical waveguides are presented. By using the field-matching method, the dispersion equation, and the mean interaction impedance for odd hybrid modes of this structure are derived. Based on our results, changing the waveguide eccentricity can improve the dispersion characteristics and the interaction impedance for oEH01 mode

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.

Mode discriminator based on mode-selective coupling

Mode discriminators based on a mode-selective coupling principle have a number of advantages. The design method of this type of discriminator is presented in this paper. The emphasis is placed on the mode-selective coupler with a multihole and multigroup of coupling holes. All of the dimensions of the discriminator are determined by this method. The calibration and power measurement of the discriminator are also investigated. Some design examples of discriminators for 35- and 70-GHz gyrotrons, which can be applied to discriminate the TE/sub 11/, TE/sub 01/, and TE/sub 02/ modes and the TE/sub 01/, TE/sub 02/, and TE/sub 03/ modes, respectively, are given.

A research of W-band folded waveguide traveling wave tube with elliptical sheet electron beam

Folded waveguide (FWG) traveling wave tube (TWT), which shows advantages in high power capacity, moderate bandwidth, and low-cost fabrication, has become the focus of vacuum electronics recently. Sheet electron beam devices are better suited for producing radiation sources with large power in millimeter wave spectrum due to their characteristics of relatively low space charge fields and large transport current. A FWG TWT with elliptical sheet beam working in W-band is presented in this paper, with the analysis of its dispersion characteristics, coupling impedance, transmission properties, and interaction characteristics. A comparison is also made with the traditional FWG TWT. Simulation results lead to the conclusion that the FWG TWT with elliptical sheet beam investigated in this paper can make full use of relatively large electric fields and thus generate large output power with the same electric current density.

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.

Study on two kinds of novel 220 GHz folded-waveguide traveling-wave tube

Two kinds of novel 220 GHz folded-waveguide (FWG) slow-wave structure (SWS) with different electron-beam tunnels are presented for producing a high power and considerable bandwidth. These structures, which have the potential to have a better performance than the conventional FWG SWS, are suitable for circle-beam electron guns and sheet-beam electron guns, respectively. In this study, the electromagnetic characteristics and nonlinear interaction between the electron beam and the electromagnetic field of the two kinds of novel FWG are investigated on the basis of simulation results. The influence of the beam tunnel with respect to its transverse shape and size on the circuit performance is investigated in detail. With different beam tunnels, the two novel FWGs exhibit similar radio-frequency characteristics and signal gain. Particle-in-cell simulation results reveal that the novel tubes exhibit a gain greater than 32 dB and a bandwidth of 10% with a 16.5 kV and 150 mA electron beam and a 90 mW peak input power. Compared with the conventional FWG SWS, the novel FWGs have 32% higher output power under optimized conditions.

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.