Ningfeng Bai

Research on traveling wave tube body temperature distribution

The paper describes simulation result of traveling wave tube(TWT) body temperature, and establishes a temperature measurement system based on the fiber bragg grating(FBG) sensor array. By quasi-distributed FBG sensing, the system can measure TWT body temperature distribution accurately.

Rayleigh scattering measurement of residual gas inside microwave vacuum electronic devices

We propose a method to measure the residual gas in microwave vacuum electronic devices (VED) in long-term storage based on Rayleigh scattering, and establish the relation between the gas state and the intensity of scattered light. This method can be used to monitor the status of VED in long-term storage.

Electromagnetic band gap substrate for planar microstrip meander line travelling wave tube

Novel dual-square electromagnetic band gap (EBG) substrate is investigated to improve the performance of planar microstrip meander line travelling-wave tube (MML-TWT). According to the simulation results, this EBG structure can improve coupling impedance double and extend bandwidth from 9.5GHz to 10.5GHz. This structure also can be fabricated in one-dimensional for the MML-TWT. In other words, it has same transverse dimension of MML-TWT, which is important to fabricate the planar travelling wave tube.

Integrated Microstrip Meander Line Traveling Wave Tube Based on Metamaterial Absorber

An integrated microstrip meander line (MML) slow-wave structure (SWS) comprised of an MML SWS and compact wideband metamaterial absorber (MMA) is proposed and demonstrated theoretically and experimentally in this paper. The MMA consists of metallic rectangular resonators with a metallic ground plane and a separating dielectric layer. Simulation results show that the MMA has multidistinctive absorption peaks; the bandwidth at 56-GHz peak frequency is reach up to 30 GHz. The integrated MML SWS can provide flatter gain response of output power than that made by the MML SWS with a traditional resistive coating attenuator. Experimental results are in close agreement with simulation results. A traveling wave tube (TWT) is simulated based on this integrated MML SWS. The output power of this TWT is 48.21 W at 33 GHz corresponding to a maximum gain of 30.3 dB; the output power gain is greater than 25 dB across the entire working frequency range.

Meta-material absorber for microstrip meander-line slow wave structure

We report the design and simulation of a metamaterial microwave triple-band absorber for microstrip meander-line slow wave structure. The compact single unit cell consists of four reversed electric ring resonators and a metallic ground plane separated by a dielectric layer. Simulation results show that the absorber has three distinctive absorption peaks which can be used to absorb the back-wave in travelling wave tube. This meta-material absorber can be used in the design of travelling wave tube, which can be helpful to fabricate slow wave structure for the travelling wave tube with microfabrication technique.

Impacts of cubic Boron Nitride (CBN) support rods on TWT performance

We propose new support rod material in helix TWTs to improve the heat dissipation performance of the tubes, which is the cubic Boron Nitride (CBN) crystal with the second highest thermal conductivity and relatively low dielectric constant. The high frequency characteristics and the beam-wave interaction of helix slow wave structure with CBN and BeO support rods are simulated and analyzed, respectively. The results show that the difference between saturated output powers is less than 10%, and backward wave oscillation power hole still exists. Temperature distribution on a TWT with CBN support rod is also obtained with lower temperature than one with BeO rods. CBN can be made as support rods of TWT with high heat dissipation capability.

Measurement experiment of residual gas inside vacuum electronic devices based on Rayleigh scattering

We performed an experiment demonstration for verifying the measurement method based on Rayleigh scattering to test the residual gas in a storing vacuum electronic devices (VED), using high pulse power ultraviolet laser and CCD detector. The normalized intensities of scattered light are obtained before and after degassing the test tube. The experimental results validate the measurement method we proposed before.

Design of low current density elliptical sheet beam gun

Low current density sheet beam electron gun is very useful for compact planar travelling wave tube (TWT). In this paper, a planner low current density elliptical sheet beam electron gun is presented, and the structure parameters of this electron gun are optimized to get low current density for the application of planar TWTs. The gun has an elliptical cathode, critical bearing on the laminarity of beam. With optimizing the structure, cathode, focusing and anode, parameters, the gun is achieved a sheet beam of 110A/cm2 at an operating beam voltage of 9.5kv with the final beam cross-section at 800μm × 60μm. The simulation results show this gun can produce a good focused laminar sheet beam.

S-shaped microstrip meander-line slow-wave structure for W-band traveling-wave tube

S-type microstrip meander-line slow wave structure was designed and simulated. The effects of different structural parameters on the new structure were analyzed. The simulation results show that this microstrip meander-line slow wave structure has a similar dispersion characteristic with the traditional structure, and the center frequency expands to the higher frequency. The transmission loss and coupling impedance is greatly improved in high frequency range.

Temperature dynamic response of slow-wave structure of space traveling wave tube

The thermal condition of slow-wave structure is very important to the normal and stable work of the space traveling wave tube. This paper theoretically analyzes dynamic response of helical slow-wave structure, and simulates it with the help of ANSYS., The dynamic response of temperature under different pulse duration and duty cycle is acquired through analysis and simulation.