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43. An $S$ -Band Long-Pulse Relativistic Backward-Wave Oscillator With Coaxial Extractor.

Author

Ge, Xingjun, Zhao, Chenyu, Zhang, Peng, Dang, Fangchao, Yang, Jianhua, and Zhang, Jun

Subjects
COAXIAL cables, RELATIVISTIC mechanics, ELECTRIC potential, ELECTRIC oscillators, ELECTRON beams
Abstract

The physical mechanism, simulation results, and main experimental results of an S-band long-pulse relativistic backward-wave oscillator (RBWO) with a coaxial extractor are presented. The central ideas of the device include: 1) dual resonant cavities replacing the cutoff neck are used to enhance the efficiency and to decrease the electric field; 2) nonuniform slow-wave structures (SWSs) are introduced in the device to improve the efficiency; 3) a coaxial extractor is well designed, which is beneficial to the extraction of generated microwaves; and 4) the diode and the collector are reasonably designed to reduce the influence of cathode and collector plasmas. In simulation, microwaves centered at 3.77 GHz are generated, with the power of 3.3 GW and efficiency of 43%. However, the pulse duration of the device does not exceed 70 ns owing to the pulse-shortening phenomenon in the initial experiment. It was found that the plasma caused by an intense radio frequency electric field on the surface of the coaxial extractor played a main role in pulse shortening. To suppress the pulse shortening, we focus on two aspects. One was to optimize the electrodynamic structures to reduce the electric field on the surfaces of the coaxial extractor while maintaining relatively high efficiency. The other was to improve the surface roughness of SWSs thereby increasing the breakdown threshold of the RF field. In the experiment after these measures were taken, microwaves centered at 3.752 GHz are generated, with the power of 2.3 GW, efficiency of 35%, repetition rate of 20 Hz, and pulse duration above 110 ns. [ABSTRACT FROM AUTHOR]

Published
2019
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44. Design and experimental demonstration of a TEM-TE10 phase shifter for high-power microwave applications.

Author

Sun, Yunfei, He, Juntao, Yuan, Chengwei, Zhang, Qiang, and Dang, Fangchao

Subjects
PHASE shifters, CIRCULAR polarizers, TRANSVERSE electromagnetic cells, CIRCULAR waveguides, MICROWAVE generation
Abstract

A novel phase shifter used to adjust the output phase of high power microwave (HPM) is investigated. The phase shifter is composed of two different circular polarizers, one of which can convert the coaxial transverse electromagnetic mode (TEM) into circularly polarized (CP) TE11 mode, and the other one can realize the transformation between the CP TE11 mode and the rectangular TE10 mode. The two circular polarizers are connected by a circular waveguide, and the TEM-TE11 circular polarizer can rotate around its axis continuously. In this way, the phase shifter can adjust the output phase of the TE10 mode in the range of 0°–360°. In this paper, the principle of a phase shifter working at 1.57 GHz, as well as the experimental results, is demonstrated. The experimental and simulation results are in good agreement. At the central frequency, the transmission efficiency in this range of phase-shifting process is over 94.6%, and the power-handling capacity is as high as 1.5 GW. This novel phase shifter is of interest to HPM spatial power combination technologies. [ABSTRACT FROM AUTHOR]

Published
2019
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47. Design and experimental demonstration of a TEM-TE 10 phase shifter for high-power microwave applications.

Author

Sun Y, He J, Yuan C, Zhang Q, and Dang F

Abstract

A novel phase shifter used to adjust the output phase of high power microwave (HPM) is investigated. The phase shifter is composed of two different circular polarizers, one of which can convert the coaxial transverse electromagnetic mode (TEM) into circularly polarized (CP) TE 11 mode, and the other one can realize the transformation between the CP TE 11 mode and the rectangular TE 10 mode. The two circular polarizers are connected by a circular waveguide, and the TEM-TE 11 circular polarizer can rotate around its axis continuously. In this way, the phase shifter can adjust the output phase of the TE 10 mode in the range of 0°-360°. In this paper, the principle of a phase shifter working at 1.57 GHz, as well as the experimental results, is demonstrated. The experimental and simulation results are in good agreement. At the central frequency, the transmission efficiency in this range of phase-shifting process is over 94.6%, and the power-handling capacity is as high as 1.5 GW. This novel phase shifter is of interest to HPM spatial power combination technologies.

Published
2019
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48. Preliminary investigation of an improved metal-dielectric cathode for magnetically insulated transmission line oscillator.

Author

Zhang X, Dang F, Zhang J, Fan Y, and Li Z

Abstract

In order to explore the cathode with good repetition quality for the magnetically insulated transmission line oscillators, an improved metal-dielectric cathode is proposed and investigated experimentally. The cathode is designed to be step-like shape, and thin copper plated boards are periodically and compactly arrayed on the surface of the cathode base, which ensures the uniformity of the electrons emitted from the cusps of the copper plated boards. According to the numerical simulation results, the step-like shape is beneficial to convert the kinetic energy of the magnetic insulating current partially and enhance the beam-wave interaction efficiency. Finally, a preliminary experiment of an L-band magnetically insulated transmission line oscillator (MILO) with the improved metal-dielectric cathode is carried out. A high power microwave (HPM) with an average power of 1.95 GW is generated from the MILO, with an efficiency of 13.5%. Under the same experiment condition, the output power and main frequency with the presented cathode are almost the same to those with the velvet cathode. Apart from that, metal-dielectric cathode has the merits of small outgassing and long lifetime, and all of these make the improved metal-dielectric cathode significantly promising for the MILO repetition operation.

Published
2015
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