Minzhi Huang

Symmetric Double V-Shaped Microstrip Meander-Line Slow-Wave Structure for W-Band Traveling-Wave Tube

A design study for a low-voltage, high-efficiency, and wide-bandwidth W-band traveling-wave tube using a symmetric double V-shaped microstrip meander-line slow-wave structure combined with a sheet electron beam is described in this paper. The electromagnetic characteristics including the dispersion characteristics, interaction impedance, and transmission characteristics of this structure are presented, and the beam-wave interaction is calculated using particle-in-cell algorithms. Our study shows that, when the design voltage and current of the sheet electron beam are set to 4570 V and 100 mA, respectively, this miniature millimeter-wave power amplifier is capable of delivering several tens of watts output power, and the peak output power is about 110 W with a corresponding gain of 31.4 dB and an averaged electronic efficiency of 12% at 94 GHz.

Review of the Novel Slow-Wave Structures for High-Power Traveling-Wave Tube

All-metal slow-wave structures are being paid great attention because of their advantages, such as good heat dissipation, high power capacity, wide passband, good wholeness of structure and large size etc. The emphases in this paper concentrate on the present state of study of four types of structures: helical groove, ring-plane, folded waveguide and periodically loaded waveguide, including theoretical analyses and practical applications. The problems and directions for future studies of these types of slow-wave circuits are also discussed. It is pointed out that all-metal slow-wave structures are suitable for applications in millimeter wave vacuum devices, like TWT, BWO, Gyro-TWT, and relativistic devices.

DESIGN OF A V-BAND HIGH-POWER SHEET-BEAM COUPLED-CAVITY TRAVELING-WAVE TUBE

The design and analysis of a high-power wideband sheet- beam coupled-cavity traveling-wave tube operating at V-band is presented. The interaction circuit employs three-slot doubly periodic staggered-ladder coupled-cavity slow-wave structure, and a 5:1 aspect- ratio sheet electron beam is used to interact with the circuit. Combined with design of the well-matched input and output couplers, a 3-D particle-in-cell model of the sheet-beam coupled-cavity traveling-wave tube is constructed. The electromagnetic characteristics and the beam- wave interaction of the tube are investigated. From our calculations, this tube can produce saturated output power over 630Watts ranging from 58GHz to 64GHz when the cathode voltage and beam current are set to 13.2kV and 300mA, respectively. The corresponding saturated gain and electron e-ciency can reach over 32.5dB and 15.9%. Compared with the circular beam devices, the designed sheet- beam TWT has absolute advantage in power capability, and also it is more competitive in bandwidth and electron e-ciency.

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.

Effect of attenuation on backward-wave oscillation start oscillation condition

In a practical helix traveling-wave tube (TWT), there is always attenuator/sever for suppressing the oscillations, including backward-wave oscillation (BWO). The factors of the influencing BWO include start position of the attenuator, its length, and attenuation quantity. In the event that the attenuator/sever and nonuniformities in the phase velocity and beam potential were considered, a linear theory is employed to analyze BWO start oscillation condition. Numerical results show that the start oscillation length of the TWT decreases when the start position of the attenuator is close to the input section of the slow wave structure (SWS), that Start oscillation current of the output section of the SWS increases as the attenuation length decreasing, or the attenuation quantity increasing or the nonuniformities becoming strong, and that, however, when the phase velocity or beam potential exceeds a particular value, no oscillation condition could be found.

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.

Analysis of the Dispersion Characteristic and Interaction Impedance of a Tape Helix Slow Wave Structure with Novel Supporting Mode

In order to enhance the power capability of the helix travelling wave tube, a novel tape helix slow wave structure (SWS), which is supported by helically arrayed radial dielectric-support posts, is developed. Each dielectric post can be easily brazed with the tape helix and the metal envelope by means of a special soldering. This kind of supporting mode can protect the dielectric supporting posts from being broken by the thermal stress in the case of high temperature. A hybrid model is set up in consideration of the influences of both the radial thickness of the tape helix and these discrete dielectric-support posts. The dispersion equation and interaction impedance of the helical SWS are obtained. The calculated results using this hybrid model presented in the paper show good agreements with the HFSS simulation results. All the results presented here can provide a good basis for designing the novel tape helix SWS.

A new metamaterial-based UWB MIMO antenna

In this paper, the design of an ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antenna based on metamaterial is proposed. The antenna is designed to achieve dual band-notched and high isolation using metamaterials. The traditional split ring resonators (SRRs) are used to achieve the band-notched effect and a new type of SRR is used to reduce the mutual coupling at both 3.1 GHz and 10 GHz. The antenna performance is presented through its S-parameters and radiation pattern. It shows the potential application in mobile devices or other small-scaled equipments.

A Modified Slow-Wave Structure for Backward-Wave Oscillator Design in THz Band

In this paper, a novel slow-wave structure (SWS), called quasi-parallel-plate (QPP), is proposed for terahertz (THz) backward-wave oscillator BWO design. Compared with the conventional SWSs, the novel SWS has a wider “cold” bandwidth and higher interaction impedance. The Particle-in-cell (PIC) results show that the BWO can produce over 0.82 W output power in the operating frequency range from 0.82 to 1 THz by utilizing an operating voltage range from 5 to 10 kV. The interaction efficiency over the entire operating frequency band is above 2.8%. This SWS, which employing a circular electron beam of 3 mA, can be considered as a promising THz SWS for BWO design with characteristics of moderate operating voltage, wide tunable bandwidth, high efficiency, and compact structure.

U-shaped microstrip meander-line slow-wave structure for Ka-band traveling-wave tube

Study on U-shaped microstrip meander-line slow-wave structure for a low voltage, wide bandwidth millimeter traveling-wave tube is presented. The electromagnetic characteristics and the sheet beam-wave interaction of this structure are carried out. The simulation results predicts that this millimeter-wave power amplifier is capable of delivering hundreds of watts output power in the frequency range of 29-38 GHz, and the peak power is about 200 watts with the correspond-ding gain of 33 dB at 35 GHz.