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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 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]

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 high power Ku-band TE01 mode gyrotron traveling wave tube amplifier (gyro-TWT) is designed and experimented in this paper. The emphasis is put on the gyro-TWT with a high average power. In the design process, a low average velocity spread magnetron injection electron gun and a wideband multichannel TE01 mode input coupler are adopted. At the same time, a high average power curved collector is also applied. To suppress the potential gyro-backward wave oscillator interactions, a new type lossy ceramic rings and lossy ceramic pieces hybrid loaded structure is used in the high-frequency interaction circuit of gyro-TWT. In hot test, the developed Ku-band TE01 mode gyro-TWT is driven by a 70-kV 23-A helical electron beam and produce a ~31.5 kW maximum saturated output average power at 16.2 GHz, corresponding to a saturated peak power of ~450 kW (7% duty ratio), a saturated gain of ~40.5 dB, an efficiency of ~28%. The measured 3-dB bandwidth is ~2.1 GHz. The gyro-TWT is found to be zero-drive stable at these operating points. [ABSTRACT FROM AUTHOR]

The design and experiment of a high power and broadband Ku-band gyrotron traveling-wave tube (gyro-TWT) amplifier operating in the TE11 mode are presented in this paper. A new-type broadband rotating TE11 mode input coupler is applied to excite operating mode and a broadband three-disk beryllium oxide ceramic output window is used in the designed gyro-TWT. In order to suppress the potential oscillations, expand working bandwidth, and improve the heat dissipation capability of high frequency system, a periodic beryllium oxide and silicon carbide composite lossy ceramic rings loaded high-frequency circuit with a nonlinear small change output taper is adopted in the gyro-TWT. When the beam voltage is 70 kV and the beam current is 12 A, the experiment of this Ku-band gyro-TWT developed shows that the measured maximum output average power is ~20 kW at the frequency 16 GHz, corresponding to a maximum output pulse power of ~200 kW (10% duty ratio), a gain of 43.0 dB and a maximum efficiency of 23.8%, −3-dB saturation gain bandwidth of 2.6 GHz (~16.3%), and −1-dB saturation gain bandwidth of 1.5 GHz (~9.4%). Under the condition of 10-W constant input power driven, the measured −3-dB constant driven bandwidth is 1.4 GHz (~8.8%). [ABSTRACT FROM AUTHOR]

A new type of input/output coupler for sheet beam traveling wave tube is designed, analyzed, and measured in this paper. In the design, a special sloped coupling aperture distributed between two paralleled rectangular waveguides in H -plane is employed for compact dimensions, ease of fabrication, attainment of high power capacity, and more convenience for periodic cusped magnet focusing system. A nonlinear-curve profile with Chebyshev-curve distribution is applied to extend the operating frequency bandwidth while suppressing reflections to avoid generating oscillation in the slow-wave structure. Based on the analytical investigation and numerical simulation, an optimized sloping angle of the coupling aperture is obtained to improved performance. Simulations imply that the coupler achieves a broadband bandwidth ( S11< -20 dB) of 23 and 10 GHz in $W$ - and $Q$ -band, respectively, with coupling coefficient above −0.2 dB. Cold test results satisfactorily agree with simulations. [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]

Gyrotron traveling wave tubes (gyro-TWTs) are of considerable interest for high-power millimeter and submillimeter radiation sources. The analytical design and experiment of a W-band gyro-TWT loaded with nonuniform periodic lossy dielectric rings is presented in this paper. The gyro-TWT is operating in the circular TE01 mode at the fundamental cyclotron harmonic, and driven by a 60 kV, 8-A gyrating electron beam with velocity ratio 1.2. Hot test results were: 1) maximum peak output power 112 kW; 2) 69.7-dB saturated gain; and 3) 23.3% efficiency at 93.5 GHz. The measured bandwidth with peak power greater than 90 kW is about 4 GHz in the range of 93–97 GHz. The hot test results show excellent agreement with the theoretical prediction. The potential backward wave oscillations involving the spurious modes TE11, TE21, and TE02 are effectively suppressed by the nonuniformly loaded periodic lossy dielectric rings. The W-band gyro-TWT is zero-drive stable at the operating points. It demonstrates that a nonuniform loaded lossy dielectric structure is excellent for suppressing potential spurious oscillations. [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]

Distributed lossy dielectric is of considerable interest for high-power milli- and submillimeter radiation sources, particularly for gyrotron traveling wave tubes (gyro-TWTs). The analytical design and experiment of a Q-band gyro-TWT loaded with periodic lossy dielectric rings operating in the circular \TE01 mode at the fundamental cyclotron harmonic are presented. The gyro-TWT is driven by a 70-kV 10-A helical electron beam with a velocity ratio of 1.0. Hot test performs maximum peak output power of 152 kW, 41-dB saturated gain, and 21.7% efficiency at 47.6 GHz. The measured bandwidth over 100 kW is at the range of 47–49 GHz. PIC simulation and large-signal prediction show excellent agreements to the hot test results. The potential backward wave oscillation interactions involving the spurious modes \TE11, \TE21, and \TE02 are effectively suppressed by loading lossy dielectric rings periodically. The Q-band gyro-TWT is zero-drive stable at the operating points, which demonstrates that loading lossy dielectric is excellent to stabilize the spurious oscillations. Moreover, the designs of magnetron injection gun, interaction circuits, and input and output structures are also achieved to satisfy the requirements. [ABSTRACT FROM AUTHOR]