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The improvement of the beam–wave interaction efficiency of the sheet beam extended interaction oscillator (SBEIO) is studied and presented in this article. A novel multi-parameter optimization scheme is developed, which is based on the simulated annealing global optimization algorithm, the nonlinear theory, and 3-D simulations, including the axial electric field distribution and the distances between each gap. The 3-D particle-in-cell (PIC) simulations are performed to verify the scheme. A $\textit {Ka}$ -band SBEIO with nine gaps is optimized with a 36.25-kV and 3.5-A electron beam. The final optimized efficiency obtained from the developed code is 31%, which shows a good agreement with the 32.6% results of the PIC simulation. Compared with the uniform axial electric field distribution, the optimized design increased the efficiency from 15.8% to 32.6%. [ABSTRACT FROM AUTHOR]

In order to enhance the power capacity of gyro-traveling wave tube (Gyro-TWT), a novel multisectorial-tunnel circuit is presented in this article. The multisectorial tunnel could extend the transverse dimension of RF circuit for higher power electron beam transportation. The azimuthal drifting and transportation distortion performance for rotated electron beam are analyzed. A multibeam magnetron injection gun (MIG) is designed. The electron beam with pitch factor of 1.09 and axial velocity spread of 3.5% is obtained. And the designed cathode was fabricated and temperature distribution was measured. It provides a possible method to enhance the power capacity of Gyro-TWT. [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 new topology to excite the HE04 mode in wide bandwidth for confocal gyro-TWAs is presented. The mode exciter consists of a TE04 mode exciter and a TE04–HE04 transition waveguide section formed by two cascaded one-stage tapers. In addition, the closed-to-open confocal waveguide boundaries are studied. Numerical results show that the port reflection of the whole structure is well below −10 dB over 90–110 GHz; the transmission of HE04 mode is better than −1 dB over 94–107 GHz. Even more important, a maximum transmission variation of less than ±0.15 dB over the 1-dB bandwidth and a mode purity of better than 97.2% over the 3-dB bandwidth are achieved. The mode exciter is compact and easy to be fabricated, which can be applied to cold-test experiments of confocal gyro-amplifiers circuits. [ABSTRACT FROM AUTHOR]

Theoretical and experimental investigations on an output system, consisting of waveguide horn, phase-shift section, RF window, and monitoring section, capable of outputting a Gaussian-like beam rather than a circular waveguide TE1,1 mode, for a Ku-band gyrotron-traveling-wave tube, have been carried out. An azimuthally symmetric Gaussian-like beam has been observed at the output port in both the low-power and high-power measurements. The experimental results showed that the mode purity of output Gaussian beam is over 98% from 14.5 to 16.5 GHz. There is no arcing monitored when the output pulse peak power is over 160 kW when the pulsed tube operates with 10% duty cycle. The output Gaussian-like beam can be directly usable for low-loss transmission as well as for effective antenna feeding and no extra mode converter is needed, which can improve the transmission efficiency of the transmission line system and form a compact high-power system. [ABSTRACT FROM AUTHOR]

In this paper a methodology to excite a circular high-order TE13-mode via a rectangular TE50 mode was proposed and verified by the millimeter wave measurement. This topology can also be applied to launch other high-order modes (HOMs) such as TE 1n , TE 2n^\prime and TE 0n^\prime (n or n^\prime =1 , 2, 3) modes via different transition rectangular TE _{m0} ( m = 2n-1$ or $m = 2n^\prime $ ) modes, which can be achieved by adjusting the number of coupling apertures and optimizing dimensions of tapered waveguides. A W-band TE13 mode converter was designed and analyzed. Two identical converters connected back to back as a proof-of-principle operating at $Q$ -band were fabricated and measured. Good performance was observed, which was in good agreement with the simulation results. This HOM converter has many potential applications in areas such as gyro-devices, high-power transmission lines, RF multimode systems of accelerators, microwave/plasma, and antenna systems. [ABSTRACT FROM PUBLISHER]

Novel compact input and output couplers for broadband operation of sheet beam traveling wave tubes are analyzed, designed, and cold tested. Multistage stepped waveguide and cascaded Bragg resonators are proposed and applied to improve the performance and extend the operating bandwidth. Optimized curve-Bragg resonators are studied to correct the phase between the reflector and $H$ -bend waveguide, which bring about a further enhancement of the coupler behavior. HFSS simulations predict a −3 dB transmission bandwidth about 38% and 34% are achieved, respectively, in Ku and $Q$ band. Besides, the large beam tunnel property of this kind of coupler benefit the beam transport of sheet beam devices. Different components as the input and output couplers for Ku- and $Q$ -band SB-TWT are manufactured and cold tested. Results of vector network analyzer measurement and simulation present an excellent agreement. [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]

RF circuit design, thermal analysis, fabrication, and measurement of a continuous wave (CW) high-power sheet beam traveling wave tube (SB-TWT) operating in the Ku-band were demonstrated in this paper. The slow wave structure circuit was constructed by double staggered grating waveguides (DSGWs), and the lossy dielectrics attached in the H-plane were applied to suppress parasitic oscillations. The Particle-in-cell simulation predicted that the CW SB-TWT can provide >20-kW output power in the band range of 16.2–18.5 GHz, with a maximum small signal gain of 38 dB. Microchannel cooling, which has been proved to be an efficient cooling method for microelectronic chip, very large scale integration, and power electronic modules with very high heat flux were introduced to improve the thermal capacity and heat dissipation ability. A thermal analysis of the RF circuit considering attenuated losses and electrons interception was studied in detail. Investigation shows that the RF circuit can operate with maximum $\sim 1$ -kW dielectric loss power (1.5 times of the loss power generated from the saturated output power at center frequency) and a maximum of 7% interception of electrons. Furthermore, an interaction circuit, including 23 DSGWs implanted with BeO–SiC to provide necessary attenuation, was fabricated and cold tested. Vector network analyzer RF measurement shows excellent performance and agrees very well with our prediction. [ABSTRACT FROM AUTHOR]