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In order to enhance the efficiency of confocal gyrotron traveling-wave tubes (gyro-TWTs), this paper is intended to present a novel triode-type magnetron injection gun for a 140-GHz 2-kW confocal gyro-TWT. This novel gun, which has a pair of sectorial emitters, is expected to obtain an axial velocity spread of 7.83% and a velocity ratio of 1.01 with an anode voltage of 35 kV and a beam current of 2.4 A. The design procedure has been given in detail. Computer simulations have been carried out using 3-D electromagnetic code computer simulation technology particle tracing. The sensitivity analysis has been performed to study the parametric dependence of modulating anode voltage, accelerating anode voltage, and cathode magnetic field on beam qualities. Results show that this novel gun can be operated stably within a certain parametric scope. [ABSTRACT FROM AUTHOR]

Design techniques and experimental results are presented on a Ku-band TE11 mode gyro-traveling wave tube. The hot test of this amplifier gives more than 153-kW output power, 2.3-GHz bandwidth (14%), 41-dB saturated gain, and 20% efficiency driven by a 63 kV, 12-A electron beam with a pitch angle (vtvz) of 1.2, and velocity spread of 5%. A linear polarized TE11 mode input coupler is used to introduce the input power. The stability of the amplifier from oscillation, including both the operating TE11 mode and the backward wave TE21 mode, has been investigated with linear codes, nonlinear self-consistent theory, and 3-D PIC CHIPIC simulation. To suppress the potential gyro-backward wave oscillator interactions, the high frequency circuit is loaded with lossy ceramic rings. The lossy structure is optimized by nonlinear theory and 3-D PIC simulation. A low velocity spread magnetron injection gun is designed with a new structure. [ABSTRACT FROM AUTHOR]

The design of a high-power low-velocity-spread space-charge-limited cusp gun is presented. The Lagrangian formulation is used to analyze the velocity spread and beam ripple (orbit center spread). It shows that the two electron orbit off-center mechanisms, the radial velocity and the nonideal cusp magnetic field, can be adjusted to cancel each other. The characteristics of the cusp gun including the cusp magnet are calculated by cosimulation employing the Maxwell2D, Matlab, Egun, and CST-PS codes. The cusp gun is designed to generate a beam of 8 A at 70 kV with a pitch factor from 1.0 to 1.8 and an axial velocity spread from 3% to 7%. The development of this cusp gun is in progress at the University of Califonia, Davis, for use in the development of harmonic gyrotrons, peniotrons, and gyro-traveling-wave tubes. [ABSTRACT FROM AUTHOR]

In this article, a compact mode selection filter and a mode converter for the 0.22-THz sheet beam traveling-wave tube (SB-TWT) has been proposed, fabricated, and tested to realize selective absorption of high-order mode without interference on the working mode. The reasonable structure and placement is explored from theory to manufacturing method in order to minimize reflection and mode distortion by junction discontinuity. Two proof-of-concept prototypes have been fabricated and tested to analyze the error sources in terahertz device. And the corresponding error models are also constructed. Final transmission data exhibit an excellent agreement with the results of computer simulations when conductor loss is taken into consideration. Such −15-dB loss performance for high-order mode is verified allowing to cover the frequency band from 0.3 to 0.315 THz. [ABSTRACT FROM AUTHOR]

The sheet beam gun (SBG) is operated at high temperature, and thermal expansion could induce huge electron beam degeneration. The previous SBG design, which did not take account of thermal expansion, obtained bad transportation performance. Experimental measurement showed that the distance variation between a cathode and an anode was larger than 0.42 mm, which could hugely degenerate beam performance. A new inner support rod with grooves was employed in this paper, and the heat power was reduced from 27 to 15.5 W, while the distance variation was reduced to 0.29 mm. The new SBG with adjustment according to the thermal expansion was fabricated and tested. The transportation rate after anode tunnel was enhanced to 98%, and the total transportation rate of sheet beam traveling wave tube with a period permanent magnet focusing structure was about 90%. [ABSTRACT FROM PUBLISHER]

A methodology to generate a circular TE13 mode for the operation of high-order mode (HOM) gyrotron-traveling-wave tubes is presented in this paper. A rectangular TE10 mode is efficiently converted into a circular TE13 mode using Y-type power dividers. Symmetric curved lossy dielectrics and dielectric rings are, respectively, positioned to suppress the potential coupling TE32 and TE71 modes according to their electric and magnetic field distribution properties. An HOM converter without dielectrics loaded was designed, constructed, and cold tested. Back-to-back transmission measurements exhibit good agreement with the results of computer simulations. [ABSTRACT FROM AUTHOR]

A new curved-profile undepressed collector designed for a planned 35-GHz gyrotron traveling-wave tube (gyro-TWT) is proposed in this paper. This gyro-TWT, which is driven by a 70-kV, 10-A electron beam, is working at the fundamental TE01 mode with an efficiency of 20% and gain of 45 dB. Studies including theoretical analysis, numerical calculation, and computational simulation have been done. Key issues concerning electronic collecting density, dissipated power distribution, transmission performance, secondary electrons, and thermal property are considered. Simulation results show that curved-profile structure collector has a better heat-handling capacity than the conventional line structure collector. [ABSTRACT FROM AUTHOR]

Overall design and cold test of a G-band gyrotron traveling-wave tube (gyro-TWT) amplifier are presented. This gyro-TWT aims at achieving a goal of 10-kW pulse output power in the range of 210–220 GHz. It is operated in a circular TE01 mode at the fundamental cyclotron harmonics, which is driven by a 50-kV, 3-A gyrating electron beam. Low velocity spread diode-type magnetron injection gun (MIG), multichannel TE01 mode input coupler, broadband metasurface output window, and lossy material loaded beam–wave interaction circuit are simulated and partially measured. Particle-in-cell (PIC) simulation shows that the designed gyro-TWT can achieve a saturated output power over 10 kW in the range of 210–228 GHz with a beam velocity spread of 2.29%. [ABSTRACT FROM AUTHOR]

In this paper, a new type input/output (i/o) structure, adopting the multiaperture coupler, for broadband sheet-beam traveling-wave tube was designed and analyzed. This novel coupling structure not only can get a larger electron passway, which will greatly benefit the transmission of the electron beam, without deteriorating electromagnetic transmission characteristics, but also work over an extremely broad bandwidth. The transmission characteristics of this coupling i/o structure are investigated by Ansoft’s high-frequency structure simulator (HFSS). Operating at TE \(_{10}\) mode, the maximum insertion loss and isolation of the i/o structure over 36–52 GHz, which equals to 36.4% bandwidth, are −25 and −20 dB, the transmission coefficient is above −0.3 dB. The results of HFSS were verified by Computer Simulation Technology Microwave Studio. [ABSTRACT FROM PUBLISHER]

Highly oversized mode converters are the critical devices for high power millimeter-wave transmission systems, characterizing high power capacity and low loss. In order to improve the conversion efficiency from TE01 to TE11 mode, the mode coupling mechanism of oversized elliptical waveguides is explored, and an optimal ellipticity interval to obtain the high conversion efficiency is deduced by analyzing the mode coupling capacity. Considering that ellipticity can affect the power capacity, breakdown thresholds of different operating modes in elliptical waveguides are studied. Based on the analyses, a synthesis method to design the elliptical mode converter integrating the mode conversion efficiency and the power capacity is proposed. A highly oversized mode converter working in $W$ -band is designed, and the simulation results demonstrate that the mode converter achieves the high conversion efficiency over 95% in a relative bandwidth of 19.6%. In order to validate the design, a prototype of the mode converter is fabricated, and the high purity of outputted TE11 mode is verified by the measurement. The oversized mode converter designed by the proposed synthesis method features high efficiency, broad bandwidth, and high power capacity, enabling its full utilization of the potential of gyrotron traveling-wave tubes (gyro-TWTs). [ABSTRACT FROM AUTHOR]

Effects of the output window reflection instability on the performance of our designed ${W}$ -band broadband gyrotron traveling wave tube (gyro-TWT) were studied by the simulation and hot test experiments. Strong oscillations and frequency self-modulation (FSM) in the after-cavity interaction (ACI) region were observed in the zero-driven state with a two-layer window and are verified with the beam-wave particle-in-cell simulation. Oscillations and FSM of 80–81.8 GHz and 91.03–94.68 GHz are, respectively, generated from the TE22 and TE02 modes in the ACI region due to the high window reflection level. By using the “sandwich” and meta-surface windows with low reflection and broad bandwidth, the parasitic ACI oscillations can be effectively suppressed. The maximum saturated output power is improved to 156.8 kW at 94 GHz and is zero-driven stable in our recent hot test experiments. [ABSTRACT FROM AUTHOR]

A circular TE0n mode content analysis technique based on the multi-mode coupler with high mode selectivity is proposed. To improve the mode selectivity, a deformed waveguide, entitled the quad-polar waveguide, which discriminates the azimuthally symmetric TE-mode on the waveguide wall, is introduced. The influence of deformation on the TE01 and TE02 modes’ field pattern, the corresponding transmission loss, and the power capacity in the quad-polar waveguide are analyzed. Based on the analysis, a dual-mode coupler of the circular TE01 and TE02 modes, consisting of an oversized deformed circular waveguide coupler and a pair of circular-to-quad-polar waveguide transitions, is designed for a high-power Ka-band gyrotron traveling-wave tube system. To verify the high mode selectivity of a quad-polar waveguide, a simple coupling with equal-radius and equal-interval holes are used. A prototype is fabricated and measured, and the results show that the coupling coefficient is −40 dB with the directivity of 27 dB for the TE01 mode, suppressing the unwanted mode TE02 mode with 53 dB. For the TE02 mode, the coupling coefficient is −40 dB with the directivity of 25 dB and suppresses the unwanted mode TE01 mode with 75 dB from 30 to 40 GHz. [ABSTRACT FROM AUTHOR]

This article explores an extremely high beam–wave interaction (BWI) efficiency technology of sheet beam traveling wave tubes (SBTWTs). An all-period phase velocity tapering optimization method is proposed to improve BWI efficiency of slow wave structure (SWS). The effects of the special electron bunching state and synchronous phase velocity change on the improvement of BWI efficiency generated by this method are analyzed. To solve the computational burden caused by dozens of parameters, self-developed 1-D nonlinear BWI code is used to calculate the BWI. For the best optimization effect, particle swarm optimization (PSO) algorithm selected from a variety of algorithms is utilized to search for the global optimal solution. The PIC simulation verification results show that by the all-period optimization method, the 80-period staggered double vane (SDV) SWS achieves a stable output power of 18 kW with 31 kV voltage 0.9-A current sheet beam at 30 GHz. The BWI efficiency of all-period phase velocity tapering SWS has reached 64.5% at center frequency, the efficiency between 28 and 35 GHz exceeds 40%. [ABSTRACT FROM AUTHOR]

A broadband dielectric window with high power handling capability for gyrotron traveling wave tubes (gyro-TWTs) had been designed based on the step-type impedance transition structure. The manufactured beryllium oxide (BeO) window can achieve a relative bandwidth of 35.3% with a maximum reflection of −20 dB in the ${X}$ -band, and the corresponding transmission loss is over −0.1 dB. The resonant spikes caused by engineering factors, including assembly tilt and gap, are investigated and analyzed. Thermal analysis shows that the BeO window can achieve a high average/CW power handling capability of over 232 kW within a wide frequency range. The fabricated input window has been successfully applied in our ${X}$ -band broadband and high-power gyro-TWT. [ABSTRACT FROM AUTHOR]

An optimum approach for designing a TE01 mode oversized waveguide bend is proposed based on angular-deformed circular waveguide. Due to the deformation of the circular waveguide cross section, the degeneracy of the TE01 mode and the TM11 mode is removed, and the mode conversion inside the waveguide bend is weakened. Characterizations of the angular-deformed circular waveguide with different deformation and its influence on the mode spectrum, the transmission loss, and the power capacity are investigated. Based on the analysis results and the coupling-wave theory, a Ka-band broadband oversized deformed circular waveguide bend with the propagating TE01 mode is designed, fabricated, and measured. A good agreement between the calculation results and the S-parameter measurement of a prototype is achieved. The transmission efficiency is over 95% in the frequency range of 26.5–35.9 GHz (the relative band is over 30%). The near-field test results further demonstrate the high output purity of the TE01 mode in the working frequency band. [ABSTRACT FROM AUTHOR]

This article proposes a longitudinal output structure in Ka-band sheet beam traveling-wave tube (SBTWT) with an ultrawideband transmission and high breakdown collector voltage. A novel electromagnetic bandgap (EBG) cutoff structure is designed to separate the slow-wave structure (SWS) and the depressed collector. The large stopband property of the EBG structure is applied to achieve not only the high transmission and the low gap leakage but also the long gap distance to provide a high breakdown voltage of the depressed collector. The 3-D simulations of a single longitudinal structure show a full Ka-band (26.5–40 GHz) reflection of less than −20 dB and gap leakage less than −0.02 dB. The entire longitudinal output collector, including two large gaps cutoff structures and the over mode electron collecting parts, is designed and manufactured. The simulations show a bandwidth of 10.4 GHz with a reflection coefficient S11 of lower than −20 dB. The cold test demonstrates the wild bandwidth of ~11.1 GHz with a reflection coefficient S11 of lower than −15 dB. The hot test reveals a stable collector dc voltage of −14.2 kV. [ABSTRACT FROM AUTHOR]

In this article, the design and experimental verification of a 200-kW Q-band gyrotron traveling wave tube (gyro-TWT) amplifier are presented. A low-velocity spread magnetic injection electron gun (MIG), a new type of multichannel TE01 mode input coupler, and a broadband double-disk output window are adopted in the design to improve the performance of the gyro-TWT. At the same time, the lossy ceramic ring-loaded high-frequency interaction circuit is constructed to provide the required loss for stable operation, and the potential oscillations are effectively suppressed. Saturated peak power of 208 kW and 12.5-kW average output power are measured at 47 GHz by hot test, corresponding to a saturated gain of 50.2 dB, an efficiency of 29.4%, and a −3-dB bandwidth of 5.5 GHz. [ABSTRACT FROM AUTHOR]

Design and microwave measurement of a linearly polarized circular TE11 mode coupler are reported in this article. Based on our earlier designed input coupler with smooth wall, we proposed an improved structure with ridges loading resulting in a bandwidth up to 29.2%. Simulation results show the port reflection S11 less than −10 dB is in 7.9–10.6 GHz. And the split transmission S21 and S31are over −3.4 dB in this frequency range. According to the simulation results, the designed input coupler is fabricated and measured with the vector network analyzer. The measurement results show excellent performance, which is in good agreement with the simulation when the conductor loss is taken into consideration. In addition, an input coupler with a cutoff waveguide is designed to improve the efficiency of single-port transmission and the power utilization. Simulation results show the transmission efficiency of the single port achieves 91%. [ABSTRACT FROM AUTHOR]

Design and measurement of a broadband compact circular TE11 mode input coupler for gyrotron traveling wave tubes (gyro-TWTs) are presented in this article. Different from the T-junction, Y-type, and multiple-hole input couplers, the proposed coupler has a merit of compact dimensions formed by the H-plane of a rectangular cavity. The simulation results show that the port reflection $S_{11}$ is less than −10 dB within 7.9–9.93 GHz. Also, the split transmissions $S_{21}$ and $S_{31}$ are over −3.4 dB in this band. It indicates that the relative bandwidth is 22.8%, and the transmission efficiency is higher than 90%. To further broaden the bandwidth, we propose an improved input coupler with ridges achieving an excellent bandwidth of 28.6%. The designed input coupler has been measured with open boundaries and matched output ports. The simulation and measurement results are in good agreement. The compact TE11 mode input coupler had been applied in our X-band gyro-TWT design. [ABSTRACT FROM AUTHOR]

This article presents the development of a dual-state Ku-band gyrotron traveling-wave tube (gyro-TWT) dual-state curved-profile magnetic injection gun (MIG) generating high-quality electron beams, in which the pitch factor is up to 1.2 and 1.35 for the pulse wave (PW) state and the continuous wave (CW) state, separately. A multiobjective genetic algorithm (MOGA) is applied in the profile optimization. Meanwhile, the parametric sensitivity is also discussed in detail. A periodic dielectric-loaded interaction circuit is adopted to suppress oscillations. Furthermore, thermal analyses of the interaction circuit under different duty cycles are also elaborated. The interaction circuit is analyzed in accordance with the proposed nonlinear self-consistent theory and particle-in-cell (PIC) codes. The results of hot experiments show that the dual-state tube obtains the output power of 150/30 kW corresponding to a saturated gain of 40/41 dB and the maximum efficiency of 25%/21% within the bandwidth of 2.0/1.1 GHz for the PW/CW state, respectively. [ABSTRACT FROM AUTHOR]

The phase characteristics of gyrotron traveling-wave tubes (gyro-TWTs) for high-resolution imaging radars have been investigated. Determinant equations of output phase are classified into the cold phase and warm phase in the cases of cold-field and hot-field regions, respectively. The phase–frequency characteristics of cold phase are examined regarding single-mode and multimode operations, respectively. The time stability and the sensitivity to external parameters of warm phase are also investigated. The efficient methods to make the output phase of gyro-TWTs controllable are proposed. The measured output phase of the input coupler and output taper of a Ka-band gyro-TWT is linear with respect to the frequency, without any distortion. Moreover, the warm output phase fluctuation introduced by the RF circuit is less than ±8°. [ABSTRACT FROM AUTHOR]

A compact and broadband circular TE01-mode oversized deformed waveguide bend for high-power transmission line is proposed in this article. In order to obtain a circular TE01 mode with high purity output, a deformed waveguide structure, entitled quad-polar waveguide, which can destroy the degeneration between the TE01 and TM11 modes and weak mode conversion inside waveguide bend is introduced. The characterization of quad-polar waveguide and its influence of deformation on the mode spectrum are analyzed. The mode coupling coefficients of quad-polar waveguide are theoretically deduced to investigate the mode conversion inside the waveguide bend. Based on the multimode coupling theory, a broadband oversized waveguide bend with propagation efficiency over 95% from 27.6 to 34.1 GHz is designed. A prototype is fabricated and measured. The average transmission efficiency is over 93% according to the S-parameter measurement. The TE01 mode with high purity output is demonstrated by the near-field test. The high-power performance is investigated by connecting it with a gyrotron traveling-wave tube (gyro-TWT), and the waveguide bend works stably under a maximum output power of 140 kW. In addition to high power and broadband, the proposed waveguide bend features compact, simple structure, and easy to machine. [ABSTRACT FROM AUTHOR]

The mode converter is a key component in a gyrotron traveling-wave tube (gyro-TWT) application system, which can transform the output circular TE $_{0n}$ modes (in a gyro-TWT loaded with lossy ceramic dielectric or photonic bandgap interaction structure, the output mode is normally a TE $_{0n}$ mode) into a mode conducive to transmission and emission (linearly polarized Gaussian-like HE11 mode). In particular, the bandwidth of the TE01–TE11 mode converter is the most important challenge in the conversion sequence. In this paper, based on the deformation of the transverse cross section and the modified multi-frequency iteration synthesis technique along the longitudinal propagation axis, a novel method for synthesis of a broad bandwidth mode converter is proposed. Then, an application of the method to a wideband serpentine TE01–TE11 mode converter with an elliptical section is given. This novel mode converter including transitional waveguides achieves a 19.18% relative bandwidth (conversion efficiency over 95%) at center frequency 30.5 GHz, which increases nearly 195% compared with the conventional circular design, and its structure length is 1151.65 mm. Overall, this method offers a novel solution to the requirement of broad bandwidth in the high-power microwave transmission system. [ABSTRACT FROM AUTHOR]

The establishment of an automatic hot test platform is one of the important conditions to ensure the safe and stable operation for the gyrotron traveling wave tubes (gyro-TWTs). In order to verify the reliability of the controlling strategies used in the long period hot test of a high peak/average power gyro-TWT, the control process of the cathode-anode beam voltage and current is described by a mathematical model based on a proportional—integral—derivative (PID) controller. The beam voltage is controlled by the high-voltage power supply and the beam current is regulated by the high-voltage power supply and filament heating power. A mathematical model of the PID controller is developed and evaluated by the MATLAB to analyze the performance of the system. The comparison between the experimental and modeling results show that the second-order inertia model with time delay can express the control process of the beam voltage and current well. The PID controlling theory can be used to model the control process of the hot test of a gyro-TWT with digital signal, so that the damage of the immature strategy is prevented. [ABSTRACT FROM AUTHOR]

In this paper, a lossy dielectric-loaded high-gain $X$ -band gyrotron traveling-wave tube (gyro-TWT) which operates at the fundamental circular TE11 mode is designed and analyzed. The designed gyro-TWT has the features of high-gain and megawatt level output power. Lossy dielectric is applied to suppress spurious oscillations and to improve the stability of the gyro-TWT. In addition, the interaction behavior of the electron beam is investigated. In the condition of 4.5 W input power, a peak RF output power of 2.14 MW with a gain of 56.7 dB at 8.4 GHz is predicted, corresponding to the electron beam-wave interaction efficiency of 35.6% at 150 kV, 40 A. The research also obtains stable output power over 1.5 MW in the range of 8–8.4 GHz with 2-W input power and output power over 1.2 MW with 150-W input power in the range of 8.6–9 GHz. [ABSTRACT FROM AUTHOR]

This paper presents the development of highly efficient gyrotron traveling-wave tube (gyro-TWT) with a nonuniform dielectric-loaded interaction circuit. The high-quality electron beam has been generated by curved-profile magnetron injection gun (MIG). With regard to the profile optimization, simulated annealing algorithm (SAA) and genetic algorithm (GA) are applied. An electron beam with a pitch factor of 1.6 and low-axial velocity spread of 0.9182% have been obtained. The parametric sensitivity is discussed in detail. A nonuniform dielectric-loaded circuit has been employed to suppress both global oscillations and local oscillations. Different thicknesses of dielectric materials have been manufactured and measured, demonstrating the circuit loss of oscillation modes that are enough for stable operation. The interaction circuit is analyzed under the guidance of nonlinear self-consistent theory and particle-in-cell (PIC) codes. The tube achieves a saturated peak output power of 36.24 kW at 93 GHz, corresponding to a saturated gain of 54 dB and a maximum efficiency of 45.3% within a 3-dB saturated bandwidth of 5 GHz. [ABSTRACT FROM AUTHOR]

A Ka-band broadband TE01-mode overmoded waveguide bend based on an elliptical waveguide structure is proposed for high-power transmission line in this paper. To investigate the mode conversion inside the waveguide bend, the mode coupling coefficients of elliptical waveguide bend are theoretically deduced. The influence of the cross section on the power-handling capacity and the transmission efficiency is studied. Calculation and simulation results present that the proposed overmoded waveguide bend has a propagation bandwidth of 7 GHz (relative bandwidth of 21%) with an efficiency over 95%. A prototype is fabricated and measured. The average transmission efficiency is over 93% in the range of 29–36 GHz according to the S-parameter measurement. The results of near-field test demonstrated that a TE01 mode with high purity is obtained at the output port of waveguide bend. The high-power performance is investigated by connecting it with a Gyrotron traveling wave tube, and the waveguide bend works stable under a maximum output power of 150 kW. The measurement results demonstrate that a novel approach is proposed successfully for the design of high-power waveguide bend. [ABSTRACT FROM AUTHOR]

Gyrotron traveling-wave tubes (gyro-TWTs) have been proved to be an attractive power source in many applications such as high-resolution radars, high-power communication systems, and electronic warfare systems. The main output indexes such as peak and average output power, interaction efficiency, and bandwidth are important for these devices. In addition, a great deal of reliability requirements such as nonstop stable operating time, operation lifetime, and environmental adaptability should be met. In this paper, detailed developing processes of gyro-TWTs in high average power operations are presented, including theoretical analyses, multiphysics simulations of key components, fabrication, and construction of the automatic hot test platform. Finally, the measured results of a Ka-band gyro-TWT for industrial applications are presented. The amplifier exhibits an excellent performance of 100-h nonstop stable operation, a 1-dB fraction bandwidth of 8%, an efficiency of more than 20%, and a peak power and an average power of more 150 and 10 kW, respectively. [ABSTRACT FROM AUTHOR]

A high-power Ku-band TE01 mode gyro-traveling wave tube (gyro-TWT) with a loss loading structure is designed, fabricated, and tested. A high beam quality magnetron injection gun generating 68-kV, 20–30-A electron beam is optimized to provide a high power radiation. A novel lossy ceramic loaded structure with mode selective attenuation ability is proposed to suppress the potential backward wave oscillation. The interaction circuit is analyzed by linear, nonlinear self-consistent theory, and experiment. An improved wideband input structure design is proposed accordingly. In the hot test, the proposed gyro-TWT produces a 420-kW maximum peak power, about 35-dB saturated gain, 23% efficiency, and more than 1.6 GHz (10%)−1-dB bandwidth in a stable operating condition. [ABSTRACT FROM PUBLISHER]

Mode converters for millimeter waves can reduce the transmission loss, generate the desired mode, and facilitate the application of high-power sources. A W-band broadband quasi-optical mode converter which converts a TE0,1 cylindrical waveguide mode into a linearly polarized Gaussian TEM00 mode has been realized and tested in this paper. The converter is composed of a wavefront transforming mirror, a polarization grating, and a phase correcting system. In order to obtain high conversion efficiency over a wide bandwidth and make the structure of the mode converter much simple and compact, the propagation path of the beam is optimized and a wavefront transforming mirror realized by an ellipsoidal mirror rather than a nonquadratic mirror is introduced. The conversion process in each section is displayed and the working principles are discussed in detail. The mode conversion characteristics are investigated by analyzing the measured radiation field pattern. Results of the measurement agree well with the numerical calculations. The proposed W-band mode converter has a conversion bandwidth of 21% when the mode conversion efficiency is over 95% and the cross polarization is below 1.7%. In addition to high conversion efficiency, low cross-polarization, and broad bandwidth, this converter features easy construction and compact structure. [ABSTRACT FROM PUBLISHER]

To accurately measure the performance of dielectric loaded circuits for gyrotron traveling wave tubes, a novel topological structure to generate the TE21○ or TE01○ (superscript represents circular waveguide) mode is proposed and verified in this paper. The topology is constituted by an overmoded TE10□ to TE20□ (superscript represents rectangular waveguide) mode converter with multiple matching steps and a taper from TE20□ to TE21○ or TE01○ mode. This topology allows the TE21○ or TE01○ mode to be excited by changing the taper dimensions. Simulation results reveal that the TE21○ and TE01○ mode converters, respectively, have a 1-dB bandwidth of 12.8 and 9.3 GHz with an excellent performance. Converters for the back-to-back millimeter-wave measurements were fabricated with computerized numerical control and wire cutting techniques. Vector network analyzer measurements are in good agreement with the simulations. [ABSTRACT FROM PUBLISHER]

Based on the previous double-staggered grating waveguide slow-wave structures (SWSs), an improved design is presented in this paper. The linear profile of the beam tunnel is replaced by a curved shape on its broad side. The high-frequency characteristics and beam–wave interaction are presented before and after the alteration. A novel approach in loading the attenuator with high attenuation is proposed to ensure a stable beam–wave interaction for the improved SWS. From our calculations, the improved SWS possesses a larger average interaction impedance with a rate of about 13.1%. Particle-in-cell simulation predicts that the saturated output power, the corresponding gain, and the electronic efficiency are all significantly improved, with an increase of more than 1-kW output power and 3-dB gain over the operating frequency range, and the maximum efficiency increases from 19.4% to 22.2%. The operating bandwidth is almost unaffected, remaining in a frequency range from 38 to 46 GHz. [ABSTRACT FROM AUTHOR]

Wider bandwidth property of traveling-wave tubes (TWTs) is continuously pursued to satisfy the increased data rates and multiple channels in modern communications. In this paper, the coalesced-mode operation instead of the general single-mode operation for the double staggered grating waveguide (DSGW) slow-wave structure (SWS) is proposed to achieve an ultrawideband property of the TWTs driven by sheet electron beam. Analytical results of the high-frequency properties for the SWS, including the dispersion characteristics, interaction impedance, and transmission property, demonstrate that the coalesced-mode operation for the DSGW is possible. A novel loading approach of the attenuator with good performance, and meanwhile, a compact configuration is proposed to suppress the potential oscillations, thus leading to a steady beam–wave interaction for the coalesced-mode operation. To verify the concept of coalesced-mode operation, particle-in-cell simulation is performed. Simulation results demonstrate that the optimized RF circuit indeed can steadily operate in coalesced mode and produce over 5-kW saturated output power ( $\sim 10$ % efficiency) in a very broad frequency ranging from 37 to 52 GHz, corresponding to a relative bandwidth of 33.7%. [ABSTRACT FROM AUTHOR]

In the above article 1 , contains the wrong data. The 2 author provides the correct below. [ABSTRACT FROM AUTHOR]