In order to develop wide-band low-loss windows for W-band vacuum electronic devices and easily fabricate them, symmetric and asymmetric pillbox windows are investigated and reported in this paper. A symmetric pillbox window and an asymmetric pillow-box window were designed, simulation optimized, fabricated, and tested. The initial parameters for the two pillbox windows were designed by equivalent circuit theory. Computer simulation technology (CST) three-dimensional (3D) electromagnetic simulation software was used to verify and optimize the design. Because of the uncontrollability of welding during the experiment, this article provides two solutions. One is to measure and reprocess the symmetrical pillbox window with the dielectric sheet welded to reduce the influence of welding on the measurement results; the other is an asymmetrical box window which is designed to avoid the error caused by the welding of the box window. The best experimental results for the symmetric pillbox window were |S21| close to 1 dB and reflection parameter |S11| close to 10 dB in the frequency range of 77–110 GHz. The experimental results for the asymmetric pillbox window were |S21| < 1 dB nearly in the frequency range of 76–109.5 GHz. The experimental results show that both solutions efficiently complete the design of broadband pillbox windows and would potentially be operated in the gigahertz millimeter-wave region.
Pressure, density, temperature, and reflectivity measurements along the principal Hugoniot of Ge-doped plastics used in Inertial Confinement Fusion capsules surrogates were obtained to pressures reaching up to 7 Mbar and compared to Quotidian Equation of State models. The experiment was performed using the GEKKO XII laser at the Institute of Laser Engineering at Osaka University in Japan. High precision measurements of pressure and density were obtained using a quartz standard and found to be in good agreement with theoretical Hugoniot curves. Modeling of reflectivity measurements show that shocked samples can be described as poor metals and that mean ionization calculated within the frame of QEOS is overestimated. Similarly, shock temperatures were found to be below theoretical Hugoniot curves. V C 2013 AIP Publishing LLC. [http://dx.
An extended interaction frequency‐locking oscillator based on carbon nanotube (CNT) cold cathode is proposed to overcome locked‐frequency limits of the conventional oscillator. Compared with the conventional oscillators, the oscillation frequency is locked by a modulation electron beam, which can be obtained in a field emission CNT cold cathode electron gun. The frequency‐locking signal does not enter the high‐frequency (HF) system but imposes an additional HF electric field on the cathode surface by a microstrip structure, which consumes considerably less power to lock the oscillation frequency. A ladder structure extended interaction oscillator operating in 2π mode is numerically investigated by three‐dimensional Particle‐In‐Cell simulation code. By analysing the impacts of different frequency‐locking power on the locked ranges, the results show that the average output power of 30.6 W is achieved at 35.11 GHz when the frequency‐locking power consumption is 460 mW. The 3‐dB bandwidth of a frequency‐locking region reaches 100 MHz.
The output/input circuit is a core component in all high-power millimeterwave (MMW) radiation sources, and its performance specifications and reliability directly impact upon the performance of the radiation device. Central to achieving high output power is the development of efficient mode converters. Here we report on the development of , a compact ka-band circular waveguide TM01-rectangular waveguide TE10 mode converter. The present mode converter adopts an all-metal waveguide structure and facilitates notable improvement in the system power capacity and is capable of realizing high-power propagation. The mode converter realizes effective mode conversion between high-order and fundamental modes, as well as allowing longitudinal and transverse transmission. Our simulation and empirical findings have shown mode purity as high as 96% in the frequency range of 32.7 -34.6 GHzwith a return loss S11 < -19.3 dB. The bandwidth of the converter is 2.4 GHz with transmission coefficient S21 ≥ -1 dB. We anticipate these results will provide a strong foundation for the development of ever more sophisticated and high power, compact vacuum electron devices and advanced radiation sources.
This paper proposes a taper cascaded over-mode circular waveguide TE0n mode converter for the millimeter and terahertz wave gyrotron. The mode converter of this structure can effectively reduce the difficulty of high frequency mode converter in fabrication. This paper verifies the feasibility of this new structure from theory, simulation, and experiment. Based on coupled wave theory calculations, three TE02-TE01 mode converters with lengths of 65.43 mm (4 segments), 119.3 mm (6 segments) and 136 mm (8 segments) and a TE03-TE02 mode converter with a length of 92 mm (8 segments) are optimized. The conversion efficiency in the frequency band 215–225 GHz is 91.8–94%, 93–95%, 95–98.78% and 95–98.44%. Because the length of the mode converter is clearly limited, this paper selects the TE02-TE01 mode converter with a length of 65.43 mm (4 segments) and the TE03-TE02 mode converter with 92 mm (8 segments) for simulation and experimental verification. In the simulation software Computer simulation technology (CST), the TE02-TE01 and TE03-TE02 mode converters and their composed TE03-TE01 mode converters are selected for modeling and analyzing. The simulation results and theoretical calculation results of the three mode converters only have different degrees of frequency deviation, and the frequency deviation of the 4-stage TE02-TE01 mode converter can be ignored; the frequency deviations of TE03-TE02 mode converter and TE03-TE01 mode converter are 2 GHz and 3 GHz, respectively. The experimental system is a field scanning system based on a vector network analyzer (VNA), which scans the input and output of the mode converter respectively. The experimental result is that when the input mode purity is 92% in TE01 mode, the output mode TE03 mode has a mode purity of 82%, and it has lower transmission loss. In this paper, the results from theory, simulation and experiment are in good agreement. This type of mode converter is easy to prepare, which makes it an effective alternative for high frequency curvilinear waveguide mode converter.
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