It is attractive to use sheet beam vacuum devices to generate high frequency, high-power microwave radiation. In this paper, we present the numerical and experimental studies of a high-power Ka-band sheet electron beam backward wave oscillator (BWO), in which the double-grating rectangular waveguide is used as the slow wave structure (SWS) for its thermal and mechanical robustness. The fundamental mode of this kind of SWS is an antisymmetric mode which has an antisymmetric longitudinal field distribution and will nonsynchronously interact with the electron beam on two sides of the electron channel along the vertical direction. We put forward a method to overcome this trouble in this paper. To drive this BWO, a high-power sheet beam is used with a cross section of 30 mm $\times\,$ 1 mm. A thin graphite cathode is used for its superiority in producing a high current, high-quality electron beam. For an experimental electron beam of 141 kV and 1668 A, the output power of over 46.8 MW at 31.68 GHz is obtained, which corresponds to a beam–wave interaction efficiency of 19.9%. Compared with the conventional hollow beam BWO and the single-grating rectangular waveguide sheet beam BWO, the double-grating sheet beam BWOs efficiency is higher, which indicates that the double-grating sheet beam device is promising for producing millimeter wave radiation with high power and high efficiency.

Study of High-Power Ka-Band Rectangular Double-Grating Sheet Beam BWO

This paper reports a Ka-band sheet beam traveling wave tube (TWT) focused by a 0.2 T closed periodic cusped magnet (PCM) system. The TWT with one section of staggered double-vane slow-wave structure (SWS) is driven by a 0.8-A sheet beam with rectangular cross-sectional area of 3.2 mm × 0.6 mm. This sheet beam TWT can produce 100 W output power, and the 3 dB band is 33–38.5 GHz. In order to improve the output power, an optimized sheet beam TWT with two sections of SWSs focused by a novel closed PCM system is proposed. The new closed PCM system is with annular magnetic blocks and can be fabricated and adjusted easily. The simulation shows that the optimized sheet beam TWT can produce 2000 W output power and the 3 dB band ranging from 33 to 40 GHz.

Study on Ka-Band Sheet Beam Traveling Wave Tube Focused by Closed PCM

Here, the tenth harmonic mixing technology based on planar GaAs Schottky diode is first proposed for the 1.1 terahertz (THz) frequency conversion module. The first higher order mode cut-off frequency of the suspended microstrip line has been investigated to determine the appropriate cross-sectional dimension of transmission line shield cavity in the radio frequency (RF) circuit portion. The height of shield cavity of transmission line is designed to be discontinuous in order to facilitate the assembly of the diode. A modelling approach combining field and circuit is used to achieve joint simulation of linear passive structure and diode non-linear characteristics. The simulation results show that the frequency conversion loss of this mixer is <55
 
dB in the RF frequency range of 1.03–1.154 THz, and the best frequency conversion loss is 50
 
dB at RF of 1.098 THz.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-map.2018.6194

1.1 THz tenth harmonic mixer based on planar GaAs Schottky diode

In this paper, by means of a 3D particle-in-cell (PIC) code, the non-linear calculation of beam-wave interaction in periodic cusped magnetic (PCM) field is presented for the X-band sheet beam klystron with five three-cell, extended interaction cavities. The simulation results show that the output peak power is more than 32.4MW, with the interaction efficiency of more than 31.2%, and the gain of more than 35.6dB.

Interaction simulation of an X-band sheet beam klystron

The paper reports on the design and performance of a high power backward wave oscillator (BWO), working at Ku-band frequencies. The rectangular waveguide grating structure is used as its slow wave structure. The backward wave oscillator is driven by a sheet beam with cross sectional area of 30mm×1mm which is generated by a thin cathode. For a beam voltage 185kV, and beam current 3.2kA, the output power is 2.5MW at 14.3GHz.

http://or.nsfc.gov.cn/bitstream/00001903-5/515866/1/9913552215.pdf

A Ku-band high power backward wave oscillator

What may be the first detailed cold test and computer simulation analysis of a Double Sheet Beam Klystron (DSBK) was performed at SLAC. The device was conceptually designed mechanically, and evaluated electrically for beam formation, gain, stability and efficiency. It is believed that the DSBK can be built at a relatively low cost for a future NLC collider and can produce at least 150 MW at 11.4 GHz with PPM focusing. Voltage and current are 450 kV and 640 A, respectively.

/pdf/a-sheet-beam-klystron-paper-design-development-of-a-sheet-4m0so3eny4.pdf

G Caryotakis

Papers

A Sheet-Beam Klystron Paper Design Development of a Sheet-Beam Klystron for the NLC