Pill-box Window Research Articles

Performing Intelligent Design of Broadband Pillbox Window for a Terahertz Traveling-Wave Tube by Using Physics-Informed Neural Network and Genetic Algorithm

Performing Intelligent Design of Broadband Pillbox Window for a Terahertz Traveling-Wave Tube by Using Physics-Informed Neural Network and Genetic Algorithm

Development of G-Band Continuous-Wave Folded Waveguide Traveling-Wave Tube

A detailed development of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$G$</tex-math> </inline-formula> -band continuous-wave (CW) traveling-wave tube (TWT) with a 160-GHz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot$</tex-math> </inline-formula> W product of bandwidth power is reported in the present work, in which the electron optics system (EOS), the tapered phase velocity folded waveguide (TPVFW) slow wave structure (SWS), the modified pill-box window (MPBW), and experimental results are described. The prototype of the proposed TWT is fabricated with optimized structural parameters obtained by particle-in-cell (PIC) simulations. Moreover, the experimental results show that TWT with 27-W output power at the frequency of 220 GHz at 100% duty cycle is obtained at the operation voltage of 17.1 kV and the current of 62 mA. The proposed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$G$</tex-math> </inline-formula> -band TWT will have broad applications in far-distance high-resolution imaging and large communications capacity.

Design and Simulation of 10-GHz Bandwidth Phase-Velocity Tapers Folded Waveguide for 108-GHz Continuous-Wave Traveling-Wave Tube

Folded waveguide (FW) traveling-wave tubes (TWT) is a typical kind of vacuum electron device (VED) with some unique characteristics of high frequency, high power, and moderate bandwidth, which are widely used in radars, communication systems, electronic countermeasure, and so on. For the application to the demonstrations of ocean communication with the frequency of over 100 GHz and continuous-wave power with 15 W, an FWTWT operating at the frequency of 108 GHz and the CW power with 50 W is designed. The optimizations of dispersion characteristics and structural parameters of this FWTWT are optimized through a detailed theoretical analysis and a particle-in-cell (PIC) simulation, respectively. For the improvements of communication quality by the increase of output power, a novel method of phase-velocity tapered (PVT) FW slow wave structure (SWS) is used. Comparing with the conventional FWSWS, the output power with the proposed scheme is enhanced 1.5 times. Moreover, the effects of angle and kinetic spreads of electron beam velocity on output power are first investigated using PIC simulations. On the other hand, for obtaining the optimum signal transmission, a tapered and modified pill-box window is presented and used as the transmission structure, which is the characteristics of the broad bandwidth and low attenuation of transmission. With the help of optimized parameters, the CW FWTWT operates at the frequency of 108 GHz, and the maximum output power, gain, and bandwidth are obtained at 78.6 W, 31.9 dB, and 11 GHz, respectively. The optimum results are beneficial to the development of CW FWTWT.

A Broad Bandwidth Metamaterial Pillbox Window for W-Band Traveling-Wave Tubes

A low voltage standing wave ratio (VSWR) broad bandwidth pillbox window with metamaterial is proposed for W-band traveling-wave tubes (TWTs) in this paper. The metamaterial structure is designed on a dielectric surface, which decreases the VSWR and broadens the bandwidth of the pillbox window. The cold-test results of the window with metamaterial are presented, which showed that the metamaterial pillbox window (MPW) achieves a bandwidth of 31.5 GHz with VSWR below 1.2, and a bandwidth of 18 GHz with VSWR below 1.1. The ghost mode and the power capacity of the window were also investigated. The results showed that the proposed metamaterial pillbox window is suitable for medium power TWTs. A Ka-band MPW was fabricated and the test results agreed well with the simulation results.

High Linear Power E-Band Traveling-Wave Tube for Communication Applications

A low-voltage and high linear power E-band traveling-wave tube amplifier is designed to meet the demand of high-data-rate wireless communication. The integrated design, including the dispersion combination of folded waveguide slow wave structure, broadband diamond pillbox window, and AlN-SiC lumped attenuator, ensures the success of the prototype tube with satisfying performance. The test results show that the amplifier is capable of providing more than 45.2 W output power, 38.8 dB saturated gain, 14.3% total efficiency, and 45.6 dB small-signal gain in 71-76 GHz band with a low voltage of 12.88 kV and a current of 80 mA. The 1 dB compression point exceeding 20 W verifies the feasibility of dispersion combination technology for high linear power design.

Over-Size Pill-Box Window for Sub-Terahertz Vacuum Electronic Devices

The pill-box window is one of the important components of microwave vacuum electronic devices (VEDs), and research into it is of great significance. As the operating frequency increases, the problems associated with the reduction in the structure size include the reduction of the brazing plane and the reduction in the tolerance of the pill-box window. These problems will cause traditional pill-box windows to be unsuitable in high-frequency bands, especially in terahertz and sub-terahertz regions. The most influential factor is the length of the circular waveguide in the box window. The welding plane of the over-size pill-box window is the annular bottom surface on both sides of the dielectric sheet, which is larger than the circular waveguide, and the operating frequency does not directly affect the area of the brazing surface. Choosing a suitable diameter for the dielectric sheet can effectively increase the tolerance to the length of the pill-box window circular waveguide. Therefore, an over-size pill-box window would be a practicable approach to improve the performance compared to the traditional pillow-box in high-frequency bands. This paper describes, in detail, the theoretical design, simulation optimization and experimental process of this improved pill-box window. An over-size pill-box window suitable for G band VEDs was successfully developed. The experimental result in the 215–225 GHz band is that the maximum transmission loss is −1 dB, and the overall transmission loss is close to −0.5 dB. The overall reflection is less than −11 dB.

Research progress of high-power waveguide window

High-power waveguide window is a critical component of high-power klystron and accelerator. The RF breakdown of the waveguide window always cause the failure of the high-power klystron. In this paper, the research progress of high-power waveguide window in the international vacuum electronics field is introduced. The research status, manufacturing requirement, and RF breakdown mechanism of the classical pill-box window are presented at first. Then the characters of some new type waveguide windows such as the tapered window, travelling wave in ceramic window, mixed-mode window, and over-mode window are summarized. Some breakdown suppression technologies like changing the material character of the window disk, changing the surface configuration of the window disk, using the positive dielectric angle, applying DC electric field or DC magnetic field, changing the waveform of transverse electric field are emphasized at the end.

A Semi-Analytic Numerical Algorithm of Diamond Pillbox Windows for Terahertz Vacuum Electron Device Applications

A semi-analytic numerical algorithm for general pillbox windows, named the pillbox window mode-matching algorithm (PWMMA), is proposed in this letter. The PWMMA shows quite consistent calculation results with CST Microwave Studio (CST-MWS) within a remarkably reduced time than CST-MWS. Four pillbox windows, each consists of a double-side metalized diamond disk, were fabricated and tested at the frequency bands of 0.21 THz-0.25 THz and 0.32 THz-0.36 THz. The experimental results of the transmission characteristics are consistent well with the calculation results of the PWMMA.

Investigation on Symmetric and Asymmetric Broadband Low-Loss W-Band Pillbox Windows

In order to develop wide-band low-loss windows for W-band vacuum electronic devices and easily fabricate them, symmetric and asymmetric pillbox windows are investigated and reported in this paper. A symmetric pillbox window and an asymmetric pillow-box window were designed, simulation optimized, fabricated, and tested. The initial parameters for the two pillbox windows were designed by equivalent circuit theory. Computer simulation technology (CST) three-dimensional (3D) electromagnetic simulation software was used to verify and optimize the design. Because of the uncontrollability of welding during the experiment, this article provides two solutions. One is to measure and reprocess the symmetrical pillbox window with the dielectric sheet welded to reduce the influence of welding on the measurement results; the other is an asymmetrical box window which is designed to avoid the error caused by the welding of the box window. The best experimental results for the symmetric pillbox window were |S21| close to 1 dB and reflection parameter |S11| close to 10 dB in the frequency range of 77–110 GHz. The experimental results for the asymmetric pillbox window were |S21| &lt; 1 dB nearly in the frequency range of 76–109.5 GHz. The experimental results show that both solutions efficiently complete the design of broadband pillbox windows and would potentially be operated in the gigahertz millimeter-wave region.

Research and optimization of a new design of output window for high power microwave tubes

A design of an output window integrated with an output resonator of the high-power klystron is proposed. The results of a theoretical study of the frequency response of an integrated window are presented. Calculation of the electric field in critical areas of the optimized design showed that the losses in the vacuum-tight dielectric are much lower, and the tangential components of the field on its surface, which are the source of breakdowns, are lower or comparable with similar parameters of traditional pillbox windows.

A Pillbox Window With Impedance Matching Sections for a -Band Gyro-TWA

A mode-matching method was developed to design a pillbox-type millimeter-wave window for a W-band gyrotron traveling-wave amplifier. With additional impedance matching sections, the pillbox window was able to achieve -40-dB reflection over a 10% frequency bandwidth. The manufactured pillbox window was achieved a maximum reflection of -15 dB. The reasons for the difference between the simulated and measured reflections were investigated.

Input coupling systems for millimetre‐wave gyrotron travelling wave amplifiers

Input couplers for millimetre-wave gyrotron travelling wave amplifiers are presented in this study. A W-band input coupling system composed of a pillbox window, a smoothly curved waveguide bend, a T-junction and a broadband reflector was numerically optimised, constructed and measured. An average transmission coefficient of -2.0dB over a designed operating frequency range was measured. Additionally, a higher-frequency input coupler for operation at a central frequency of 372GHz was also designed based on a multiple-hole coupling configuration. The simulated transmission coefficient was -0.5dB if the ohmic loss is not considered.

Design of a high gain and high efficiency W-band folded waveguide TWT using phase-velocity taper

The folded-waveguide (FW) slow-wave structure (SWS) is a very promising beam-wave interaction circuit for high-frequency traveling wave tubes (TWTs). This paper presents the design methodology for enhancing the gain and efficiency of a practical W-band FWTWT using phase-velocity taper. Initially, phase-velocity, interaction impedance, and gain-growth of a single-section FWTWT are predicted theoretically. Further, these parameters are optimized using the eigenmode solver and transient solver of 3-D CST Studio. The simulated results agreed with theoretically predicted results within ~1% discrepancy. Then the single-section SWS along with the input and output couplers consisting of quarter-wave impedance transformers and pillbox windows are simulated using transient solver and a return-loss of around −20 dB is obtained over the desired band. Finally, the output power, gain and electronic efficiency for a two-section TWT with the phase-velocity taper are obtained using particle-in-cell simulation of CST Studio. At an applied beam voltage of 20 kV and a current of 0.1 A, an output power of 130 W, corresponding to a saturated gain of 39.4 dB, an instantaneous 3-dB bandwidth of around 5.3%, and electronic efficiency of around 6.5% at 94 GHz has been obtained. It was found that at 94 GHz the ‘positively and negatively phase-velocity tapered’ sections enhanced the gain by almost 3 dB and doubles the electronic efficiency of the two-section FWTWT design as compared to the two-section FWSWS with the same interaction circuit length with no phase-velocity taper.

Design and simulation of a sub-terahertz folded-waveguide extended interaction oscillator

In this paper, an interesting type of a two-section folded wave-guide (TSFW) slow wave structure (SWS) for the development of sub-Terahertz (sub-THz) extended interaction oscillator (EIO) is proposed. In this sub-THz device, the prebunching electron beam is produced by the TSFW SWS, which results in the enhancement of the output power. To verify this concept, the TSFW for sub-THz EIO is developed, which includes the design, simulation, and some fabrications. A small size of electron optics system (EOS), the TSFW SWS for beam-wave interactions, and the output structure are studied with simulations. Through the codes Egun and Superfish, the EOS is designed and optimized. With a help of CST studio and 3D particle-in-cell (PIC) simulation CHIPIC, the characteristics of beam-wave interaction generated by the TSFW are studied. The results of PIC simulation show that the output power is remarkably enhanced by a factor of 3, which exceeds 200 W at the frequency of 108 GHz. Based on the optimum parameters, the TSFW is manufactured with a high speed numerical mill, and the test transmission characteristic |S21| is 13 dB. At last, the output structure with a pill-box window is optimized, fabricated, integrated, and tested, and the result shows that the voltage standing-wave ratio of the window is about 2.2 at an operating frequency of 108 GHz. This design and simulation can provide an effective method to develop high power THz sources.

Design and Comparison of Waveguide Windows

The waveguide Windows used in most of the high power microwave Tubes are of different types, namely the rectangular single block window, the multilayer window and the thin disc pillbox window. In this paper, the design of all the three types of windows is carried out in the X-band frequency. The design of the single block window has been carried out with inductive, capacitive and resonant type of irises to find their suitability for window applications. The results obtained from the equivalent circuit have been compared with that of results from the Electromagnetic software HFSS and presented for all the RF windows.

Q波段回旋行波管新型盒型输出窗的设计

Q波段回旋行波管新型盒型输出窗的设计

Research on the development mechanism: from two-sided multipactor to one-sided multipactor

Multipactor discharge always causes disastrous damage to a vacuum window in high power microwave system, which actually becomes a limiting factor for the output power of vacuum device. To explore the multipactor phenomenon of complicated pill-box window, the mulitpactor in normal field between the metal boundary and the window disk is studied. Through Monte Carlo (MC) simulations, the susceptive curve is fitted and analyzed. The secondary electrons' avalanche behavior under the normal RF field is discussed. It is noticed that the one-sided multipactor is excited within a very limited Vrf-fD region when two-sided multipactor is excited initially. The development condition from two-sided multipactor to the one-sided multipactor is proposed. Through analyzing and MC simulation, the condition is achieved. When the normal RF electric field can satisfy the phase focus conditions of one-sided multipactor, the two-sided multipactor will develop into one-sided multpactor and then reach a saturation value. Meanwhile, the initial effect of electrostatic field on one-sided multipactor is also discussed. On condition that two-sided multipactor can be excited, the number of secondary electrons can increase up to a saturation value when Edc0 is lower than the minimal saturate value of Edc. When Edc0 is lager than the minimal saturate value of Edc and in the Edc/Erf threshold of one-sided resonant multipactor, the number of secondary electrons can also increase to a saturate value. However, When Edc0 is lager than the minimal saturate value of Edc but beyond the Edc/Erf threshold of one-sided resonant multipactor, secondary electrons will be suppressed.

Theoretical and Experimental Study of the Modified Pill-Box Window for the 220-GHz Folded Waveguide BWO

The modified pill-box window is designed and manufactured as a power-coupler part of the 220-GHz folded waveguide backward wave oscillator in the Institute of Applied Electronics. Owing to the modified structure, both the fringe area and the end area of the thin dielectric window piece can be metalized, thus the reliability of vacuum seal and strength can be greatly improved compared with its traditional counterpart. An analytical method is developed from the previous equivalent circuit theory of the traditional pill-box window. According to the analytical expressions, the inner parameter of the modified pill-box window is roughly designed. The 3-D computer code is used to verify and further optimize the analytical design. The calculation shows good consistency between the theoretical and the numerical methods. The resonant modes in this oversized window system are also numerically calculated to demonstrate that it is difficult to remove all the modes from the operating frequency range. Fortunately, the error analysis shows that these possible spurious modes are hardly stimulated in the window system with TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode injected, when the misalignment of each transmission section can be limited to the practical mechanical tolerance. For this requirement, an innovative mechanical structure is then proposed to guarantee the precision of the parameters of window system which can nicely restrain the variations caused by the brazing process. By carefully controlling the errors in machining, assembly, and brazing process, the brazed and nonbrazed samples are finally manufactured and tested. The experimental result indirectly demonstrates that the microwave circuit design and the mechanical design is reasonable and reliable, where the reflection ratio is <0.1 between the frequency range of 215–225 GHz.

The suppression effect of a periodic surface with semicircular grooves on the high power microwave long pill-box window multipactor phenomenon

To improve the transmitting power in an S-band klystron, a long pill-box window that has a disk with grooves with a semicircular cross section is theoretically investigated and simulated. A Monte-Carlo algorithm is used to track the secondary electron trajectories and analyze the multipactor scenario in the long pill-box window and on the grooved surface. Extending the height of the long-box window can decrease the normal electric field on the surface of the window disk, but the single surface multipactor still exists. It is confirmed that the window disk with periodic semicircular grooves can explicitly suppress the multipactor and predominantly depresses the local field enhancement and the bottom continuous multipactor. The difference between semicircular and sharp boundary grooves is clarified numerically and analytically.

Development of new pill-box window for S-band high power klystron

In this paper, a new pill-box window with arc groove disk is studied for S-band high power klystron. Its main characteristics are long pill-box and periodic grooved window disk. The long pill-box window can decrease the normal field and relieve the radio frequency loss in high power transmission, and periodic grooved window disk can suppress tangential field multipactor. The Monte Carlo (MC) method is used to build up the simulation model and analyze the increasing tendency of electrons. The simulation results indicate that long-box window with periodic arc grooved window disk can restrain multipactor effectively. Homocentric circular half-camber arc slot is put forward to overcome the disadvantages of periodic straight triangle and strait rectangular. The long pill-box with groove disk window prototype is tested in high power Travelling Wave Resonant Ring (TWRR) and the experimental results show an excellent character of this window.