This article focuses on the design and stability study of the TM220 2 pi-mode of the double-gap output cavity of the multiple-beam klystron, which consists of the four fundamental mode subcavities with seven beamtunnels inside each of them. First, based on the 3-D electromagnetic simulation, the basic designs of the output cavity, mode converter, and output system were completed, and the specific cold test method for the gap impedance was provided. To address the complex mode oscillation problem introduced by the high-order mode scheme, combined with particle-in-cell (PIC) simulation calculations, an absorber combination scheme was proposed to suppress or attenuate the oscillation modes. The klystron integrated with this output circuit was tested. During the hot testing, the stable power output and on-site spectral data demonstrated the effectiveness of the output cavity's mode stability design.

This paper designs a 20 MW high-peak-power klystron in the C-band. The operating voltage of this Cband klystron is 210 kilovolts, the perveance is $2 \mu \mathrm{p}$, and the calculated efficiency is 50%. Miniaturization is achieved through periodic permanent magnet focusing. The paper presents the main design results, including beamwave interaction, electron optics, and magnetic focusing system.

This article presents the simulation and cold test of a dual-gap output cavity of an X-band multi-beam klystron. This output cavity is loaded with one-stage-filter, and operates in the TM $2202 \pi$ mode, with $4 * 7$ electron beam channels. The calculations and analyses are conducted on the filter, field pattern, characteristic impedance, frequency intervals, etc. The measuring method of gap impedance suitable for the output cavity of $T M_{220}$ mode has been developed.

Objective From a structural standpoint, the klystron is a narrowband device that realizes beam-wave interaction through a sequence of independent resonant cavities. Advances in simulation techniques and computational methods for klystrons, as well as advancements in electric vacuum materials, manufacturing processes, and related technologies, have continuously enhanced their power and bandwidth performance. For example, high-power wideband klystrons are now widely applied in radar and communication systems. X-band wideband klystrons have achieved megawatt-level output pulse power, offering substantial utility in a range of radar applications. To satisfy the bandwidth demands of microwave electronic systems, research into wideband klystron technologies is increasingly prioritized. Expanding the bandwidth of the klystron output section is therefore a critical technology in the development of broadband klystrons. Methods Current approaches to expanding the frequency bandwidth of klystrons primarily rely on techniques such as staggered tuning of resonant cavities, integration of waveguide filters at the output cavity, and utilization of overlapping mode configurations in Multi-Gap Output Cavity (MGOC). The output section of high-frequency structures typically adopts a double-gap coupled cavity, for which gap impedance testing methods are relatively well established. Building on this foundation, a triple-gap coupled output cavity structure is developed, enabling further bandwidth enhancement. The flatness of the gap impedance across the operating band of an MGOC directly determines the gain and bandwidth performance of the klystron. Therefore, accurate calculation and testing of gap impedance are essential. This study proposes a method for calculating MGOC impedance based on cavity equivalent circuit theory. The MGOC is modeled as a resonant circuit comprising capacitive and inductive elements, and the gap impedance matrix is derived using the mesh current method. Based on microwave network theory, a corresponding experimental method for measuring MGOC impedance is also proposed. By analyzing the phase of the reflection coefficient at the output coupling port under various conditions-including all gaps open, single-gap short-circuits, and localized perturbations at individual gaps-the gap impedance within the frequency band of the cold test sample is determined. Using this theoretical framework, an X-band four-gap output cavity structure is designed. The gap impedance of the fabricated sample is measured to verify the validity of the proposed method. Results and Discussions The form of the MGOC impedance derived using equivalent circuit theory is presented (Equation 6). The experimental model of the X-band four-gap output cavity is constructed, and the optimized electrical parameters for each cavity are listed (Table 1). The calculated frequency bandwidth over which the internal impedance exceeds 3 300 Omega in the X-band reaches 1 200 MHz (Fig. 3). This represents a 30% increase compared to the triple-gap cavity and a twofold improvement over the double-gap cavity, meeting the expected design performance. The structural dimensions of the X-band four-gap output cavity are summarized (Table 2). A schematic of the MGOC modeled as an (n+1)-port microwave network is shown (Fig. 5). By solving for the impedance at the output coupling port, the relationship between the output port and other ports is obtained (Equation 13). The impedance for the all-gaps-open condition is given (Equation 14). The impedance for the case where a single gap is short-circuited and all other gaps remain open is derived (Equation 15), and the impedance corresponding to a perturbation in any single gap capacitance, with the remaining gaps open, is expressed (Equation 16). Based on transmission line theory, the impedance at each gap is calculated using these three sets of expressions (Equations 26 similar to 29). Using this theoretical framework, the X-band four-gap cavity prototype is fabricated and tested. To support structural optimization, the four fundamental mode field distributions of the four-gap cavity are first analyzed (Figs. 6 and 7). The parameters obtained via the equivalent circuit method are refined and adjusted for the cold test component. The final measured impedance distribution of the X-band four-gap cavity is presented (Fig. 9). The measured bandwidth, with a gap impedance exceeding 3 400 Omega, reaches 1 185 MHz, which closely agrees with the calculated result based on the equivalent circuit model. Conclusions This study proposes a method for calculating the gap impedance of a klystron MGOC based on the mesh current approach within the cavity equivalent circuit framework. A design scheme for an X-band four-gap output cavity is presented, and its impedance bandwidth is compared with those of triple-gap and double-gap cavities. The calculated bandwidth of the four-gap cavity is 33% greater than that of the triple-gap design and twice that of the double-gap counterpart. Building on this, a measurement method for MGOC gap impedance is developed using microwave network theory. Cold test experiments are conducted on an X-band four-gap cavity prototype. The measured results closely match the theoretical predictions, with the impedance exceeding 3 400 W across nearly 1.2 GHz of bandwidth. Moreover, the proposed cold measurement technique enables the estimation of mutual impedance between cavity gaps by measuring impedance with any two gaps in a short-circuited state. This capability offers important insights into the coupling behavior among cavity modes. These findings provide a robust theoretical and experimental foundation for advancing broadband klystron technologies.

This article introduces the design and experimental study of a Ku-band continuous wave tunable klystron. The device mentioned above adopts a single electron beam and six tunable resonant cavities, it operates at a cathode voltage of 9.5 kV, and the cathode emission current is 1.05 A with an axial guiding magnetic field of 0.34 T. To reduce the heat dissipation of the collector and improve the efficiency, the device adopts a four-stage depressed collector design, and the collector adopts forced air cooling for heat dissipation. Finally, the assembled sample tube is tested in detail. The dc beam transmission is over 99% and the high-frequency beam transmission rate is above 97%. The device can output continuous wave power of over 2.6 kW in 1.2-GHz tuning frequency range, with 1-dB instantaneous bandwidth (BW) exceeding 60 MHz at each working frequency channel. Tube gain exceeds 51 dB, and efficiency exceeds 40%. The experimental results are in good agreement with those obtained by the 1-D and 3-D simulation. The development of this device provides important technical reference for wideband mechanically tuned klystron products and has significant importance.

Continuous wave tunable klystron is a microwave amplifier widely used in satellite earth stations. This type of klystron has outstanding characteristics of high efficiency and long lifespan. This article proposes a design scheme of an electron optical system for Ku-band continuous wave tunable klystron. The klystron adopts a depressed collector to improve the overall efficiency of the device, and the collector area is cooled by forced air. The emission current density of the cathode and the temperature of the drift channel and collector in klystron during the rated operating condition directly affect the device lifespan. The distribution of electron trajectories is simulated using 2-D and 3-D electromagnetic calculation software, and a thermal analysis simulation of the klystron structure is conducted. A reliable klystron design scheme was obtained through the above process, and it is experimentally verified under the testing of a klystron sample tube. The DC electron beam transmission rate of the klystron exceeds 99%, and high-frequency output state beam transmission rate is above 97.5%. During the testing process, the klystron can maintain a stable working state. This study laid an important technical foundation for the development of Ku-band tunable klystrons.

An electron optics system of an X-band gate-controlled multibeam klystron has been designed and tested. This tube operates in the high-order mode of TM210 and has two independent modules of the cathode and heater. The primary difficulties of the electron optics system operated in high-order mode are the low electron beam transmission and the mode oscillations. Through simulation and mode analysis, this article has obtained methods to improve electron beam transmission and suppress oscillations. Several tubes have been manufactured and tested. Both design considerations and experimental results have been presented. The agreement between the test results and the simulations further validates the rationality of the design.

Tunable continuous wave klystrons, as the final power amplifiers, are widely used for uplink signal transmission in the satellite earth stations. Electron gun is the core component of the klystron, its stability determines the performance of the whole device. This article presents the design of a high perveance electron optical system for Ku band tunable continuous wave klystron. On this basis, the influence of electron gun structure design on cathode thermal efficiency is discussed, the electron gun sample is presented and the emission test is carried out. In condition of low working ratio pulse, the experimental results show that the pass rate of the electron beam is above 99%, and the pass rate under high frequency signal output state is more than 97.5%. This study has laid an important technical foundation for the development of tunable continuous wave klystrons.

This paper presents the design and measurement results of an X-band broadband klystron with a peak power of 1MW developed at Aerospace Information Research Institute, Chinese Academy of Science (AIRCAS). In the development of this klystron, the single electron beam with an electromagnetic focusing system was adopted to achieve a high beam transmission rate. Meanwhile, a filter-loaded over-lapping mode double gap coupling cavities output circuit (OMDGOC) and a pill-box output window were used to ensure the klystron has an operating bandwidth of 650MHz. The 1# klystron was tested under a 1 % duty ratio at 27 operating frequency points. The technical specifications of this klystron are as follows: peak power: over 1MW, efficiency: over 24.3 %, gain: over 37.1dB, beam transmission rate: over 96%, which meet the design requirements.

This paper has completed the simulation of the X-band 1 MW klystron electronic optical system, and optimized the electron gun and focusing system respectively. The electron gun adopts a single electron beam scheme. The voltage and current of the beam is 80 kV and 45 A respectively, the perveance is about 2.0 μP , and the average emission current density of the cathode is 6.81 A/ cm 2. The focusing system adopts the design of electromagnetic focusing, and the maximum magnetic field in the uniform area is about 0.33 T. The calculation results show that the distribution of the electric field lines in the electron gun area is uniform, the fluctuation of the electron beam is uniform, and the DC pass rate of the electron beam reaches 100%, which meets the design requirements.

The triple-gap cavity technology is an important means to expand the bandwidth of the klystron output circuit. In order to realize 1 GHz output bandwidth for $X$ band klystron, the equivalent circuit simulation of the triple-gap cavity is carried out. The actual cavity size is determined by the designed electrical parameters and the cold test model is processed. Based on the microwave network analysis theory and perturbation theory, a test method for the gap impedance of the triple-gap cavity was designed, and the output circuit of the klystron with a bandwidth of 1 GHz (9150 MHz-10150 MHz) was tested, which laid an important technical foundation for the development of broadband klystrons.

A continuous wave X-band klystron producing output power of 4 kW and bandwidth of over150MHz has been designed in Institute of Electronics, Chinese Academy of Sciences (IECAS). The design, manufacture, and test results have been reported in this paper. The results indicate that the performance of the tube satisfies the design requirement. The improved tube has a beam transmission rate over 97%, and operates very stably.

In [1], the authors would like to make the following corrections.

A model of the metal-grating periodic slow-wave structure (SWS) with dielectric loaded in the grooves was built and the expressions of the dispersion equation and coupling impedance were developed by using the Borgnis function and the field-matching method. Under the assumption of the dilute electron beam, the gain was obtained. Through numerical calculations, the influences on the high-frequency characteristics of some parameters are given. Moreover, the different characteristics of the two ways of the dielectric being loaded have been analyzed.

A linear theory of bilateral metal-grating periodic slow-wave structure (SWS) with a sheet electron beam is developed. The field-matching method has been used at the upper and bottom waveguide boundaries where the metal-grating structure is used to slow down the electromagnetic phase velocity. The derived dispersion equation has been solved through the iterative technique. The influences of the structural asymmetry on the linear growth rate have been analyzed as well.

本文简要地报道了中国科学院电子学研究所对X波段带状注速调管所做的研究工作,其目的是对这种新方案进行原理性的验证.这项研究包括两个阶段,在第一个阶段中,成功建造并测试了使用闭合周期磁聚焦方案的带状注电子光学束管,在第二个阶段中,完成了高频互作用结构的设计并制造了完整的X波段带状注速调管.实验中,在125 kV附近观察到了器件的放大特性.在输入功率0.71 kW,工作频率11.69 GHz时,带状注速调管输出功率达到了2.8 MW,3 dB带宽30MHz,增益35.96 dB,效率32.52％,束流通过率73.3％.在工作电压135 kV时,可以观察到大于93％的束流通过率,然而,此时管内出现振荡.这项研究表明带状注速调管有望在高功率的场合中获得应用,同时,寻求抑制振荡的方法仍然是未来研究中的艰巨任务.

The dispersion equation of nonstaggered bilateral metal-grating periodic slow-wave structure inside a parallel plate is derived. Under the condition that the groove widths of the upper and lower sides are equal with each other, R n has been replaced by R, where R n is the reflection coefficient of the nth harmonic wave. The validity of this process on Rn has been proved by rigorous derivation. Using the iterative technique, the dispersion relation of the bilateral grating structure in asymmetric structure is solved. The numerical results show that the second higher mode of this structure is more suitable for the beam-wave interaction and by adjusting the degree of asymmetry, some high-frequency performances of this mode can be effectively improved.

A linear theory of a nonstaggered bilateral metal-grating periodic slow-wave structure with a sheet electron beam is developed using the Borgnis potential function and field-matching method. The field-matching method has been used at the upper and bottom waveguide boundaries where the metal-grating structure is used to slow down the electromagnetic phase velocity. The derived dispersion equation has been solved through the iterative technique. Numerical calculations show the effects of some parameters on the linear growth rate. Moreover, the influences of the structural asymmetry on the linear growth rate have been analyzed as well.