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In this paper, converters of TE $^{\Box }_{{10}}$ –TE $^{\circ }_{{21}}$ mode and TE $^{\Box }_{{10}}$ –TE $^{\circ }_{{01}}$ mode with similar exciting topologic structures are designed and verified for a cold test of gyro-TWT. Both the proposed converters are composed of three sections, including TE $^{\Box }_{{10}}$ to TE $^{\Box }_{{20}}$ mode converter with ridged twist waveguide, TE $^{\Box }_{{20}}$ to TE+22 mode converter with variable cross-shaped waveguide, and the last section TE+22 to TE $^{\circ }_{{21}}$ or TE $^{\circ }_{{01}}$ mode converter ($^{\Box }$ represents the rectangular waveguide, + represents the cross-shaped waveguide, and ° represents the circular waveguide). The mode converters can be designed step-by-step and exhibit excellent wideband performance and high conversion efficiency. Simulation results reveal that the proposed TE $^{\circ }_{{21}}$ mode and TE $^{\circ }_{{01}}$ mode converters have less than 0.04 and 0.03 dB loss over 13.5- and 12-GHz bandwidths, respectively, while the return loss is below −25 dB. Prototype TE $^{\circ }_{{21}}$ and TE $^{\circ }_{{01}}$ mode converters were fabricated and back-to-back millimeter-wave measurements were performed to verify the design. [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]

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]

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]

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]

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]

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]