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In order to reduce the ohmic losses in the slow wave structure (SWS), an elliptical pillar defected photonic crystal waveguide (EPDPCW) is proposed as a SWS for the terahertz traveling wave tube (TWT). Compared with rectangular pillar defected photonic crystal waveguides (RPDPCW), the EPDPCW shows better high-frequency characteristics and lower ohmic losses. According to the particle-in-cell (PIC) results, in the frequency range of 188 GHz to 218 GHz, the saturated output power of EPDPCW is greater than 13.4 W, and the maximum saturated output power is 26.8 W at 196 GHz at a voltage of 9.78 kV and a beam current of 150 mA. Compared to the RPDPCW-TWT, the performance of the EPDPCW-TWT has been significantly improved. [ABSTRACT FROM AUTHOR]

For the purpose of improving performance and reducing the fabrication difficulty of terahertz traveling wave tubes (TWTs), this paper proposes a novel single-section high-gain slow wave structure (SWS), which is named the symmetrical quasi-synchronous step-transition (SQSST) folded waveguide (FW). The SQSST-FW SWS has an artificially designed quasi-synchronous region (QSR) to suppress self-oscillations for sustaining a high gain in an untruncated circuit. Simultaneously, a symmetrical design can improve the efficiency performance to some extent. A prototype of the SQSST-FW SWS for 650 GHz TWTs is designed based on small-signal analysis and numerical simulation. The simulation results indicate that the maximum saturation gain of the designed 650 GHz SQSST-FW TWT is 39.1 dB in a 34.3 mm slow wave circuit, occurring at the 645 GHz point when a 25.4 kV 15 mA electron beam and a 0.43 mW sinusoidal input signal are applied. In addition, a maximum output power exceeding 4 W is observed at the 648 GHz point using the same beam with an increased input power of around 2.8 mW. [ABSTRACT FROM AUTHOR]

A new slow wave structure (SWS), named E-plane loaded sine waveguide (EPLSW) SWS is proposed for the development of G-band traveling wave tubes (TWTs). The structure, derived from the sine waveguide (SW) SWS, features staggered rectangular gratings on the two E-planes, intersecting with the sine-shaped gratings. The natural electron beam tunnel lies between these gratings. The EPLSW-SWS offers improved characteristics compared to the conventional SW-SWS. High-frequency simulation studies reveal that the passband of the EPLSW-SWS extends by more than 33 GHz over the SW-SWS under identical dispersion conditions. Additionally, the interaction impedance of EPLSW-SWS surpasses that of the SW-SWS in the frequency range of 195–255 GHz. Further analysis through particle-in-cell (PIC) results presents that when operating at 19.5 kV and 145 mA for the sheet beam current, it attains a maximum saturated power of 132.7W and a 3 dB bandwidth exceeding 50 GHz. [ABSTRACT FROM AUTHOR]

Terahertz (THz) backward wave oscillators (BWOs) hold immense potential for a broad range of industrial and military applications. This study presents a comparative analysis of 0.34 THz sheet beam (SB) and circular beam (CB) folded waveguide (FWG) BWOs. We examined the design, simulation (CST MWS and PS, HFSS), and performance, revealing that sheet beam BWO outperforms circular beam BWO in terms of interaction impedance, power, efficiency, and bandwidth. Under 20 kV beam voltage and 10 mA beam current conditions, sheet beam BWO achieves 0.47 Ω (0.34 THz) interaction impedance, 0.65 W output power, and a bandwidth of approximately 12 GHz, surpassing the 0.18 Ω , 0.23 W, and 8.5 GHz values of circular beam BWO, respectively. Furthermore, this study encompasses the fabrication and thorough characterization of the sheet beam BWO's slow-wave structure. Experimental validation confirms its effectiveness, with measured S 11 demonstrating reflection below - 10 dB and S 21 exhibiting transmission above - 2 dB. [ABSTRACT FROM AUTHOR]

Terahertz backward wave oscillators based on double corrugated waveguides are enabling devices for modern satellite communication systems. This research focuses on the design of a 0.34 THz double corrugated waveguide-based interaction structure using a sheet beam. This choice allows the use of shorter pillars along with a narrow gap between pillar rows. Shorter pillars are easier to manufacture and a narrow gap is required for better interaction impedance. Circular beams restrict the use of larger pillars and narrow gap between pillars. The performance of this interaction structure is compared with a folded waveguide. Under the same operating conditions involving a 20 kV beam voltage and a 30 mA beam current, the double corrugated waveguide interaction structure exhibits impressive performance in simulations, featuring an interaction impedance of 0.52 Ω at 0.34 THz, an output power of 3.2 W, and a bandwidth extending to approximately 20 GHz. In contrast, the folded waveguide, as per simulation results, registers values of 0.43 Ω , 2.6 W, and a 12 GHz bandwidth, respectively. The proposed double corrugated waveguide-based interaction structure is fabricated using modern CNC machining. Experimental validation reinforces the effectiveness of this design, with measurements indicating reflection below −20 dB and transmission exceeding −2 dB. [ABSTRACT FROM AUTHOR]

In order to improve the performance of sine waveguide (SW) traveling wave tube (TWT), an elliptical beam-tunnel sine waveguide (EBTSW) slow wave structure (SWS) is proposed. EBTSW-SWS not only has high interaction impedance in a relatively wide frequency band but also has an elliptical beam-tunnel. The simulation results of high-frequency characteristics show that, under the same dispersion, the passband of EBTSW-SWS increases by 30% compared to the SW-SWS, and the average interaction impedance of EBTSW-SWS is higher than that of SW-SWS in almost the whole passband. Moreover, the particle-in-cell (PIC) simulation results reveal that under the operating voltage of 20.8 kV and beam current of 150 mA, EBTSW-TWT can provide more than 70 W of saturated output power in the frequency range of 200-260 GHz, reaching the maximum power of 151 W at 220 GHz with the maximum electronic efficiency of 4.85%. [ABSTRACT FROM AUTHOR]

A $Q$ -band traveling-wave tube (TWT) with profiled helix pitches and profiled inner diameters of slow wave structure (SWS) is proposed. The transmission characteristics of the $Q$ -band TWT are simulated by the Computer Simulation Technology (CST). In the operating frequency band (36.5–41.5 GHz), the simulated voltage standing wave ratio (VSWR) is less than 1.5. In addition, the beam–wave interaction is simulated to predict the performance of the $Q$ -band TWT when the beam voltage and beam current are 8.5 kV and 60 mA, respectively, and the axial focusing magnetic field is 0.4 T. In the operating frequency band, the self-oscillation is well suppressed, and the device efficiency of the $Q$ -band TWT exceeds 63.5%, and the saturated output power and gain exceed 83 W and 45 dB, respectively, especially the device efficiency can reach the maximum of 69.5% at 37 GHz. When it is backed off 6 dB from the saturation, the device efficiency exceeds 40.5%, up to 42.7% at 39 GHz. Preliminary experiments have confirmed the design. These results show that the proposed $Q$ -band TWT has important applications to the next generation wireless communication system with high efficiency. [ABSTRACT FROM AUTHOR]

The angular log-periodic meander-line traveling wave tube (TWT) is a kind of low voltage, small-sized, high power, low cost, on chip amplifiers, and considered as a key part of the advanced communication systems, the future biomedical applications and the next electronic counter measure (ECM) instruments et al. Here, an angular log-periodic meander-line TWT is presented in this article. The angular log-periodic meander-line slow wave structure (SWS) is supported by two diamond rods. The dispersion and the impedance characteristics are analyzed in detail. In order to reduce the reflection loss, a gradual ridged waveguide is connecting the input–output standard rectangular waveguide to the meander-line SWS. The particle in cell (PIC) simulations show that the output power of the TWT can reach 55 W at 34 GHz with the operation voltage of 1800 V and the beam current of 0.2 A. The SWS is manufactured by a laser machine with Molybdenum sheet. The assembled TWT is tested and the results show that the ${S}_{{11}}$ is less than −10 dB at 30–39 GHz. The ${S}_{{21}}$ mismatch between the simulated and the measurement is discussed at the end. [ABSTRACT FROM AUTHOR]

A novel electron-optical system (EOS) for ${G}$ -band traveling-wave tubes (TWT) is investigated by simulation and verified by experiment. The EOS includes a sheet beam electron gun, a tunable periodic cusped magnetic focusing (TPCMF), and a collector. An elliptical focus electrode (FE) featuring a simple geometry and easy fabrication is utilized to compress the pencil beam into the sheet beam with a cross section of 0.4 mm $\times0.1$ mm. The electron gun with a cylindrical cathode of 0.8 mm diameter generates the sheet beam with voltage of 22 kV and current of 115 mA. Based on the sheet beam electron gun, the TPCMF with easy assembly and compact size is then proposed. The experimental results show that the beam transmission is 92.1% within a beam tunnel (its length 21.2 mm and cross section 0.8 mm $\times0.15$ mm). The EOS is suitable for ${G}$ -band TWT. [ABSTRACT FROM AUTHOR]

A novel sine groove waveguide slow wave structure (SGW-SWS), originated from the sine waveguide (SW), is proposed for a wideband terahertz (THz) traveling wave tube (TWT). SGW-SWS not only has high interaction impedance in a relatively wide frequency band, but also has a wide beam tunnel. In addition, it can be fabricated using the Nano-Computer Numerical Control (CNC) milling techniques. The high-frequency simulation results show that, under the same dispersion, the passband of SGW-SWS is 23 GHz wider than that of SW-SWS, and the average interaction impedance of SGW-SWS is higher than that of SW-SWS in the whole passband. And the transverse dimension of beam tunnel is independent of the dispersion characteristics of SGW-SWS, so the beam current can be further increased by enlarging the size of beam tunnel. Moreover, the particle-in-cell (PIC) simulation results reveal that the saturated power and electronic efficiency of SGW-TWT in the frequency range of 201–260 GHz are more than 84.9 W and 2.72%, respectively, when the operating voltage is 20.8 kV and the beam current is 150 mA. [ABSTRACT FROM AUTHOR]

In this article, a novel dielectric-supported staggered dual-meander-line (DS-SDML) planar slow-wave structure (SWS) is proposed for a traveling wave tube (TWT) working at ${E}$ -band. The proposed staggered arrangement of meander-lines (MLs) leads to a stronger beam–wave interaction and achieves higher output power as compared to the symmetric arrangement. The input–output couplers have been designed by using staggered stepped double ridge waveguide, to connect the standard ${E}$ -band rectangular waveguide and the DS-SDML SWS. An attenuator and pitch tapering have been applied to the proposed SWS to suppress the unwanted frequencies and to improve the output power. Particle-in-cell (PIC) simulation results show that for an 11.8-kV, 200-mA sheet-beam, the output power can reach 283 W at 75 GHz, with a maximum gain and electronic efficiency of 34.5 dB and 11.9%, respectively. [ABSTRACT FROM AUTHOR]

The miniaturized traveling wave tube (TWT) is a kind of high-efficiency, high-power, long-lifetime power amplifier which is an attractive choice for many applications, such as outer space exploration, phased array radar detection, unmanned aerial vehicle (UAV) communication, and on-chip application. In this article, a sheet beam miniaturized TWT with V-shaped meander-line slow wave structure (SWS) supported by two trapezoidal ceramic rods is designed. First, the dispersion characteristics, the impedance characteristics, and the S-parameters of the V-shaped meander-line SWS are analyzed in detail. Then, the particle-in-cell (PIC) simulation results predict that the TWT can produce 512-W output power driven by a 7.1 kV, 0.3-A sheet beam with a rectangular cross-sectional area of 3.5 mm $\times0.1$ mm. The TWT can cover the whole ${X}$ -band when the operation voltage shift from 7.1 to 9.1 kV. At last, the V-shaped meander-line SWS is manufactured, assembled, and tested. The good agreement between the simulated and the measured ${S} _{\mathbf {11}}$ has been achieved and the mismatch between the simulated and the measured ${S} _{\mathbf {21}}$ has been discussed at the end. [ABSTRACT FROM AUTHOR]

The microstrip meander-line traveling wave tube (TWT) is a kind of small sized, low voltage, low cost, and easy to fabricate TWT. It is an attractive choice for many applications, such as communication systems, phased array radars, security detectors, and electronic counter measure (ECM) instruments. In this paper, a Ka band U-shape meander-line slow wave structure (SWS) supported by a diamond rod is presented. The dispersion characteristics of this meander-line SWS are analyzed using CST MW Studio. The S-parameter simulation results show that the reflection is below − 15 dB between 32 and 38 GHz, and the particle-in-cell (PIC) simulation reveals that this meander-line TWT can produce 57 W output power at 36 GHz, when it is driven by a 8.1 kV, 0.04 A sheet beam with rectangular cross-sectional area of 1.0 mm × 0.12 mm. This meander-line SWS is manufactured, assembled, and tested. The good agreement between the simulated and measured S11 has been achieved and the mismatch between the simulated and measured S21 has been discussed at the end. [ABSTRACT FROM AUTHOR]

A dual-beam planar slow wave structure (SWS), named dielectric supported ring-bar SWS is proposed in this paper. The planar SWS is supported by two dielectric rods at the side edges, making it fit for dual sheet beam operation. The high frequency and transmission characteristics of the proposed SWS are investigated. The backward-wave oscillation and higher harmonic waves are effectively suppressed by setting two cathodes in the same plane parallel to the SWS and negative phase-velocity jumping. The hot performance of the proposed SWS is carried out by using particle-in-cell (PIC) simulation, in which two sheet electron beams (9.7 kV, 0.2 A) are employed to provide direct current power. With an input power of 1W, the output power is 180 W at 38 GHz and the corresponding gain is 22.6 dB. Besides, after adding dielectric rods to the output part, the entire structure dissipates heat well by thermal analysis. [ABSTRACT FROM AUTHOR]

A novel slow wave structure (SWS), named staggered double corrugated waveguide (SDCW), is proposed for the development of wideband high-power terahertz (THz) traveling wave tubes (TWTs). The SDCW-SWS not only has the wideband characteristic of staggered double grating (SDG) but also has the high interaction impedance characteristic of symmetrical double grating. In addition, its tunnel width is independent of the lower cutoff frequency and can be further increased. Numerical Eigen mode calculations show that, under the same dispersion, the passband of SDCW-SWS is increased by more than 10 GHz compared with SDG-SWS, and the average interaction impedance at 195 GHz is increased by about 62%. A particle-in-cell simulation analysis confirms that the average output power, saturated gain, and electron efficiency of SDCW-TWT at 195 GHz are ~110 W, ~20.34 dB, and ~5.46%, respectively, when the operating voltage is 20 kV and the beam current is 100 mA. Therefore, SDCW is a promising slow wave circuit of wideband high-power THz traveling wave amplifier. [ABSTRACT FROM AUTHOR]

A novel modified angular log-periodic folded waveguide slow wave structure (MALPFW-SWS) is proposed for high-gain traveling wave tubes (TWTs). Each unit of the MALPFW-SWS has different dispersion characteristics and thus it has the ability to suppress oscillations in TWTs. The dispersion equation of the MALPFW-SWS is derived and a Ka-band MALPFW-SWS is designed according to the dispersion equation for verification. The particle-in-cell (PIC) simulation indicated that the output signal is steady even the gain of the designed MALPFW-TWT reaches 40 dB. The frequency spectrum of the output signal also proved that the MALPFW-SWS can suppress oscillations. The cold test experiment results show that the transmission characteristics of the fabricated MALPFW-SWS are good and are in good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

A novel Ka-band azimuthal supported angular log-periodic strip-line (ASALS) slow wave structure (SWS) is proposed for a miniature radial sheet beam traveling wave tube (TWT). In the proposed SWS, two dielectric rods are employed to support the ASALS at both azimuthal sides. The strip-line is made of high-melting metal; thus, the ASALS SWS has a higher power capacity than microstrip SWSs. The high-frequency characteristics of that proposed SWS are investigated by using simulation software. The ASALS SWS is then fabricated and assembled for cold test. The measured transmission loss and reflection loss are better than − 2.5 dB and − 10 dB, respectively. The hot performance of the proposed is studied based on particle-in-cell (PIC) simulation. It is shown that when the operating voltage is 5700 V, the ASALS TWT can give a maximum output power of 320 W at the frequency of 39 GHz, corresponding to a gain of 14.9 dB and electron efficiency of 9.12%. [ABSTRACT FROM AUTHOR]

A novel slow wave structure (SWS), called double tunnel staggered grating (DTSG), which originates from the double staggered grating (DSG) and folded waveguide (FW), is proposed to develop a dual-beam traveling wave tube (TWT) with high power and electron efficiency in Terahertz (THz) band. Using two key techniques: (1) the rectangular holes are opened in the grating-ridges, and the operating mode is cut-off at holes; (2) specific grating-height, the DTSG-SWS possesses the wide operating band as DSG-SWS, high interaction impedance as the rectangular grating (RG) SWS, and good transmission characteristics as FW-SWS. In addition, it is not only suitable for the dual-beam TWT, but also is simple and easy of fabrication as DSG-SWS. The particle-in-cell simulation analysis confirms that the saturated power and electron efficiency of TWT using DTSG-SWS have been significantly improved compared with the TWT using DSG-SWS. [ABSTRACT FROM AUTHOR]

In order to further improve the output power of W-band traveling wave tube (TWT), a low gain TWT was proposed as a secondary amplifier. It uses a double staggered grating slow wave structure (DSG-SWS) and a sheet beam. Firstly, the design of DSG-TWT was given. Through simulation, the DSG-TWT could provide a saturation output power of more than 1000 W in the frequency range of 93–97 GHz, and the maximum output power could reach 1200 W at 95 GHz. No oscillation and current interception were found. Then DSG-SWS was fabricated by E-plane partition method using high-precision CNC milling. The SWS was fed with a high-power input-output coupler which consists of a mode converter and an impedance transformer. Simulation and cold-test results were presented, showing that the S11 is less than −10 dB and the voltage standing wave ratio (VSWR) is less than 2.0 in the frequency range of 93–100 GHz. [ABSTRACT FROM AUTHOR]

A novel helical groove rectangular waveguide slow wave structure (HGRW-SWS) which evolves from the double staggered grating waveguide (DSGW) SWS is put forward to develop the high-gain and high electron efficiency terahertz (THz) traveling wave tube (TWT). The major advantages of the HGRW SWS are the higher interaction impedance, lower ohmic loss, and lower phase velocity especially in higher frequency band compared with the DSGW SWS. The gain and electron efficiency of TWT using HGRW-SWS have been significantly improved, respectively, compared with the TWT using DSGW-SWS. [ABSTRACT FROM AUTHOR]

High-power vacuum electron devices (VEDs) are attractive, because of their broad applications, such as advance radars, electromagnetic warfare, and plasma reactors. In this paper, a Ka band mega-watt sheet electron beam traveling wave tube (TWT) is reported. A two-staged rectangular waveguide grating slow wave structure (SWS) driven by a sheet electron beam (20 mm × 1 mm, 164.8 kV, 850 A, 20 ns) is used in this TWT. In order to suppress the self-excited oscillation, a rectangular BeO attenuator is inserted between the two-staged SWSs. The experimental results show that the TWT can produce more than 2 MW output power from 34.2 to 35.5 GHz. And the maximum output power is 4.24 MW at 35 GHz, corresponding to the gain of 25.9 dB. In the future, the TWT will be used to perform research on biomedical effects and imaging. [ABSTRACT FROM AUTHOR]

Variable-width technology applied to the folded waveguide traveling wave tube (FW-TWT) is proposed in this paper to suppress the lower band-edge oscillation and to expand the operating bandwidth when the operating frequency shifts toward the lower band for obtaining larger output power. Changes in the width of the slow wave structure (SWS) determine the variation of the lower-cutoff-frequency (LCF), which makes the LCF's distribution a frequency range rather than a specific frequency-point. The lower band-edge oscillation will not be focused on a special position but distributed in a frequency-band range in which multiple oscillation modes compete with each other near the LCF. The lower band-edge oscillation can be suppressed by mode competition to some extent. In addition, the width variation of SWS also results in the phase-velocity variation, and thus, the operating bandwidth of FW-TWT can be further improved by the optimized design of variable-width-SWS parameters. Beam-wave interaction simulations predicted that power and bandwidth improvements have been achieved without the lower band-edge oscillation. Meanwhile, four solutions are given for further certifying the effectiveness of the variable-width method in lower band-edge oscillation suppression and bandwidth widening. An output power level of over 350 W in a frequency range of 85–90 GHz (5 GHz) is obtained, with a maximum power of ∼648 W and an electron efficiency of ∼12.1% at 88 GHz with a beam current of 260 mA and a beam voltage of 20.5 kV. [ABSTRACT FROM AUTHOR]

A 140-GHz folded-waveguide traveling wave tube (FWG-TWT) with a relatively larger circular electron beam tunnel was designed and developed. Using simulation software, the high frequency characteristics, the transfer characteristics, and the beam-wave interaction of the TWT were studied in detail. The simulation predicted up to 98 W output power and about 43 dB gain of FWG-TWT at the center frequency. The input and output couplers compatible with the FWG-SWS and the periodic permanent magnet focusing structure were designed. The FWG-TWT thus designed was fabricated and tested. The experimental result shows the output power exceeding 1.6 W and the gain exceeding 25 dB at 140 GHz when the input power is 5 mW. The reasons for the departure of the experimental from the simulated results have been explained. [ABSTRACT FROM PUBLISHER]

In this paper, a wideband 220-GHz sheet-beam traveling-wave tube (TWT) based on staggered double vane slow-wave structure (SWS) is investigated. A novel method of loading the attenuator into the SWS for suppressing backward wave oscillation is proposed. In addition, a novel focusing electrode of the sheet beam gun is carried out in this paper, which is a whole structure but divided into two parts artificially, one is used to compress the electron beam in $X$ -direction and the other is used to compress the electron beam in $Y$ -direction. In addition, a novel anode is redesigned to reduce the defocusing effect caused by the equipotential surfaces. A nonuniform periodically cusped magnet is used for focusing the sheet electron beam, which is predicted to exhibit 100% beam transmission efficiency in a 75-mm length drift tube. The high-frequency characteristics of the SWS and the beam-wave interaction are also studied. The results reveal that the designed TWT is expected to generate over 78.125-W average power at 214 GHz, and the 3-dB bandwidth is 31.5 GHz, ranging from 203 to 234.5 GHz. [ABSTRACT FROM PUBLISHER]

It is attractive to use sheet beam vacuum devices to generate high frequency, high-power microwave radiation. In this paper, we present the numerical and experimental studies of a high-power Ka-band sheet electron beam backward wave oscillator (BWO), in which the double-grating rectangular waveguide is used as the slow wave structure (SWS) for its thermal and mechanical robustness. The fundamental mode of this kind of SWS is an antisymmetric mode which has an antisymmetric longitudinal field distribution and will nonsynchronously interact with the electron beam on two sides of the electron channel along the vertical direction. We put forward a method to overcome this trouble in this paper. To drive this BWO, a high-power sheet beam is used with a cross section of 30 mm $\times\,$ 1 mm. A thin graphite cathode is used for its superiority in producing a high current, high-quality electron beam. For an experimental electron beam of 141 kV and 1668 A, the output power of over 46.8 MW at 31.68 GHz is obtained, which corresponds to a beam–wave interaction efficiency of 19.9%. Compared with the conventional hollow beam BWO and the single-grating rectangular waveguide sheet beam BWO, the double-grating sheet beam BWOs efficiency is higher, which indicates that the double-grating sheet beam device is promising for producing millimeter wave radiation with high power and high efficiency. [ABSTRACT FROM PUBLISHER]

A phase shift that is caused by the machining errors of independent circuits would greatly affect the efficiency of the power combination in traditional multi-beam structures. In this paper, to reduce the influence of the phase shift and improve the output power, a multi-beam shunted coupling sine waveguide slow wave structure (MBSC-SWG-SWS) has been proposed, and a multi-beam overmoded flat-roofed SWG traveling wave tube (TWT) based on the MBSC-SWG-SWS was designed and analyzed. A TE10-TE30 mode convertor was designed as the input/output coupler in this TWT. The results of the 3D particle-in-cell (PIC) simulation with CST software show that more than a 50 W output power can be produced at 342 GHz, and the 3 dB bandwidth is about 13 GHz. Furthermore, the comparison between the single-beam sine waveguide (SWG) TWT and the multi-beam overmoded SWG TWT indicates that the saturated output power of the multi-beam overmoded SWG TWT is three times more than that of the single beam SWG TWT. [ABSTRACT FROM AUTHOR]

An attenuator supporting meander-line (ASML) slow wave structure (SWS) is proposed for a Ka-band traveling wave tube (TWT) and studied by simulations and experiments. The ASML SWS simplifies the fabrication and assembly process of traditional planar metal meander-lines (MLs) structures, by employing an attenuator to support the ML on the bottom of the enclosure rather than welding them together on the sides. To reduce the surface roughness of the molybdenum ML caused by laser cutting, the ML is coated by a thin copper film by magnetron sputtering. The measured S11 of the ML is below −20 dB and S21 varies around −8 dB to −12 dB without the attenuator, while below −40 dB with the attenuator. Particle-in-cell (PIC) simulation results show that with a 4.4-kV, 200-mA sheet electron beam, a maximum output power of 126 W is obtained at 38 GHz, corresponding to a gain of 24.1 dB and an electronic efficiency of 14.3%, respectively. [ABSTRACT FROM AUTHOR]