Sheet Beam Traveling Wave Tube Research Articles

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

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.

RF Design, Thermal Analysis, and Cold Test of a Ku-Band Continuous Wave Sheet Beam Traveling Wave Tube

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.

Theoretical analysis and design optimization of wideband input/output branch waveguide couplers for a sheet beam traveling wave tube

The branch waveguide coupler (BWC) with an intrinsically excellent microwave property in an extremely wide frequency range was proposed to build the input/output (I/O) structure for the sheet beam traveling wave tube. The odd and even mode theory is utilized to analyze the BWC. Based on the theory, a code is written to calculate its microwave performance parameters. The numerical calculation has a good agreement with the computation simulation. To improve the efficiency of developing the BWC, a novel design optimization approach based on the MATLAB optimization tool is proposed. A BWC with nine branch waveguides is optimized using multi-objective genetic algorithm. In addition to the excellent microwave property, a compact configuration is achieved. It is predicted that the I/O structure possesses a very good performance with coupling above −0.3 dB, port reflectivity under −19 dB, and isolation less than −15 dB in a broad frequency range of 37.4–51.0 GHz, corresponding to a bandwidth of 13.6 GHz (30.7%).

A 3-D Large Signal Model for Sheet Beam Traveling Wave Tubes

A 3-D frequency domain large signal code called sheet beam traveling-wave tube 3-D (SBTWT3-D) for illustrating the nonlinear beam-wave interaction in the SBTWT is presented in this paper. A recent published field theory model for illustrating the staggered double-grating arrays waveguide (SDGAW) slow-wave structure is adopted in the code to obtain the RF circuit fields' distribution and ohmic loss. The sheet beam is simulated by a set of discrete rays. The ac and dc space-charge fields are obtained by solving the discrete Helmholtz equations and the discrete Poisson equation, respectively. A 3-D nonlinear beam-wave interaction analysis for a W-band SDGAW SBTWT is performed and the calculation results are compared with those obtained from time-domain 3-D particle-in-cell simulations.

Study on Wideband Sheet Beam Traveling Wave Tube Based on Staggered Double Vane Slow Wave Structure

In this paper, a wideband 220-GHz sheet-beam traveling-wave tube (TWT) based on staggered double vane slow-wave structure (SWS) is investigated. A novel method of loading the attenuator into the SWS for suppressing backward wave oscillation is proposed. In addition, a novel focusing electrode of the sheet beam gun is carried out in this paper, which is a whole structure but divided into two parts artificially, one is used to compress the electron beam in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula> -direction and the other is used to compress the electron beam in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Y$ </tex-math></inline-formula> -direction. In addition, a novel anode is redesigned to reduce the defocusing effect caused by the equipotential surfaces. A nonuniform periodically cusped magnet is used for focusing the sheet electron beam, which is predicted to exhibit 100% beam transmission efficiency in a 75-mm length drift tube. The high-frequency characteristics of the SWS and the beam-wave interaction are also studied. The results reveal that the designed TWT is expected to generate over 78.125-W average power at 214 GHz, and the 3-dB bandwidth is 31.5 GHz, ranging from 203 to 234.5 GHz.

Extremely Broad Bandwidth Input/Output Coupling Structure Design for a &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;\(Q\) &lt;/tex-math&gt;&lt;/inline-formula&gt;-Band Sheet-Beam Traveling-Wave Tube

In this paper, a new type input/output (i/o) structure, adopting the multiaperture coupler, for broadband sheet-beam traveling-wave tube was designed and analyzed. This novel coupling structure not only can get a larger electron passway, which will greatly benefit the transmission of the electron beam, without deteriorating electromagnetic transmission characteristics, but also work over an extremely broad bandwidth. The transmission characteristics of this coupling i/o structure are investigated by Ansoft's high-frequency structure simulator (HFSS). Operating at TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode, the maximum insertion loss and isolation of the i/o structure over 36-52 GHz, which equals to 36.4% bandwidth, are -25 and -20 dB, the transmission coefficient is above -0.3 dB. The results of HFSS were verified by Computer Simulation Technology Microwave Studio.

A novel 140-GHz sheet-beam folded-waveguide traveling-wave tube

A novel folded-wave guide (FWG) slow-wave structure (SWS) with sheet-beam tunnel is presented for the high-power and considerable bandwidth in terahertz (THz) wave band. Its electromagnetic characteristics and nonlinear interaction between the electron beam and the electromagnetic field were investigated. A novel input and output coupler was proposed that could produce good input and output matches. The particle-in-cell simulation results revealed that the tube can be expected to produce over 100 W of average power in the range from 141 to 146 GHz, assuming an RF input signal with an average power of 45 mW. Compared with the conventional folded-waveguide traveling-wave tube (FWGTWT) at 140 GHz, the novel FWGTWT had a 48% higher output power, and the novel FWGTWT can operate at same frequency band with larger dimensional parameters. Meanwhile, the novel FWG was also much shorter than the normal FWG with good performance at the working frequencies. It, therefore, will favor the miniaturized design of a high-power terahertz wave band traveling-wave tubes (TWT).

System Design Analysis of a 0.22-THz Sheet-Beam Traveling-Wave Tube Amplifier

The primary constituents of a 0.22-terahertz (THz) sheet-beam traveling-wave tube (TWT) amplifier, composed of a staggered double grating array waveguide, have been designed for broadband THz operation (~ 30%) using the fundamental passband (TE-mode). Currently, we are looking into the possibility of a pulsed low-duty test of this device as a proof of principle (POP) and have been making efforts to construct the system. The optimally designed input coupler has ≤ 1 dB insertion loss at 0.22 THz with ~ 75 GHz (34%) 1-dB matching bandwidths. A thin mica RF window provides a coupling bandwidth spanning multiple octaves. The collector is designed to have a jog for collecting the spent beam along the RF path coupled to the output RF window. Computer simulations show that the collector hybridized with a WR-4 window has ~ 60 GHz matching bandwidth with ~ - 0.5ndB insertion loss at 0.22 THz. The hybrid periodic permanent-magnet design combined with the quadrupole magnet (PPM-QM), intended for low-duty pulse operation in a proof-of-concept experiment, allows the elliptical sheet beam from an existing gun (25 : 1 aspect ratio) to unoptimized gun to have 73% beam transmission. The POP pulsed test is designed to be matched to our existing system, which will thereby tolerate beam transmission. However, a proper gun for the sheet-beam tunnel of the designed circuit will provide much better transmission. In our prior works, we successfully proved at W-band that the magnet design provided >; 99% beam transmission of a 10:1 aspect ratio sheet beam. Most of the TWT circuit components have been designed, and currently, a full simulation modeling effort is being conducted.

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Modeling Investigation of an Ultrawideband Terahertz Sheet Beam Traveling-Wave Tube Amplifier Circuit

Extensive numerical analysis has demonstrated that a terahertz (H-band) sheet beam traveling-wave tube (TWT) amplifier circuit, composed of a staggered double grating array waveguide, has very broad bandwidth (~30%) of the fundamental passband (TE mode) with a 7:1 aspect ratio sheet beam without excitation of n = 1 space harmonic backward-wave modes. Particle-in-cell (PIC) simulations utilizing MAGIC3D and CST PS predict that the designed circuit produces ~150-300-W output power, corresponding to ~3%-5.5% intrinsic electronic efficiency (~35-38-dB saturated gain from 50-mW input driving power), over ~25% bandwidth, which is in good agreement with CHRISTINE 1-D code predictions. Simulations, using a perfectly matched layer boundary (~ -30-dB return loss), show that the circuit stably operates without noticeable oscillation. With a more realistic matching condition (~ -9.5-dB return loss), it becomes unstable. However, simulations show that the incorporation of an attenuating sever with tapered conductivity suppresses the instability in tube operation.

Investigation of terahertz sheet beam traveling wave tube amplifier with nanocomposite cathode

Particle-in-cell simulations of a staggered double grating array traveling wave tube intended as a wideband amplifier for terahertz communications, sensing, and imaging applications showed that, for an electron beam power of 5 kW, it produces 150–275 W, corresponding to 3%–5.5% electronic efficiency, at 0.22 THz with over ∼30% bandwidth and with greater than 12 dB/cm growth rate. The circuit has been fabricated by both UV lithography and high precision computer-numerical-control machining with ∼2–3 μm dimensional tolerance and ∼50 nm surface roughness. A scandate nanocomposite (Sc2O3–W) cathode for the electron beam source has successfully emitted 120 A/cm2 (space charge limited) at 1150 °C and 50 A/cm2 at 1050 °C for 8000 h as required to produce the requisite high current density electron beam.