Jirun Luo

Theory and experiments of electromagnetic loss mechanism for microwave heating of powdered metals

The physical explanation of electromagnetic loss mechanism for microwave heating of powdered metals is presented in this letter. A theoretical model is proposed to simulate and analyze the heating process. An experiment has been performed to prove the theory.

Wideband Microstrip Bandpass Filter Based on Quadruple Mode Ring Resonator

A novel wideband microstrip band-pass filter is presented in this letter based on a quadruple-mode ring resonator, which is developed by introducing a stepped-impedance one-wavelength ring resonator (SORR) into a stepped-impedance half-wavelength resonator (SHR). In order to suppress the harmonic responses of the filter for a wide stop-band, two band-stop sections with asymmetrical -type structure are introduced. A prototype filter having 49.3% of 1 dB and 57.9% of 3 dB fractional bandwidth is fabricated with advantages of high selectivity and high out-of-band rejection. In the pass-band, the return loss is larger than 18.8 dB and at the centre frequency insertion loss is 0.6 dB. The experiments are in good agreement with the simulations.

Linear theory of the electron cyclotron maser based on TM circular waveguide mode

A linear theory of the electron cyclotron maser, which is applicable to any TM circular waveguide mode, is developed by using Laplace transforms. This theory can be used to analyze the linear behaviors of both the TM mode gyrotron traveling wave tube (gyro-TWT) and the TM mode gyrotron backward wave oscillator (gyro-BWO). Numerical results show that, although the TM mode is less effective than the TE mode for the gyro-TWT interaction, the TM mode may be as effective as the TE mode for the gyro-BWO interaction, even in the case of weak relativistic electron energy.

Initial experimental results of a new triplet harmonic-multiplying gyrotron amplifier (Gyrotriotron)

A new triplet gyrotron amplifier, which we call gyrotriotron, has recently been developed. The device consists of a gyroTWT input stage to modulate the beam at S/sub 1/=1 cyclotron harmonic, a four-unit clustered-cavity as intermediate stage to bunch the beam at S/sub 2/=2 cyclotron harmonic and a gyro-TWT output stage to extract energy from the bunched beam at S/sub 3/=2 cyclotron harmonic. Electronic coupling between neighboring stages is realized through ballistic beam bunching in the radiation-free drift space similar to what happens in a gyroklystron. Because S/sub 3/ = S/sub 2/ = 2S/sub 1/, the device is a harmonic multiplying gyrotron amplifier with a scheme of 1-2-2. The clustered-cavity employed in the gyrotriotron is a group of TE/sub 03/ mode-selected cavities, which are closely adjacent and without any coupling between them.

Predistortion Linearization of an X-Band TWTA for Communications Applications

Using a predistortion linearizer is an important way to improve traveling-wave tube amplifier (TWTA) linearity. However, predistortion linearizers cannot usually control amplitude modulation (AM)/AM and AM/phase modulation (PM) conversion separately, so it is difficult to satisfy linearization requirements for AM/AM and AM/PM conversion simultaneously. This paper proposes a predistortion linearizer with a relatively simple circuit structure, which provides good control of gain expansion over the input power dynamic range while keeping the amount of phase expansion small. Good linearity improvement has been obtained for a 45-W X-band TWTA with this predistortion linearizer.

A new triplet gyrotron amplifier, the gyrotriotron

Summary form only given. A new triplet gyrotron amplifier, which we call gyrotriotron, has recently been developed. The device consists of a gyro-TWT input stage to modulate the beam at S/sub 1/=1 cyclotron harmonic, a four-unit clustered-cavity as intermediate stage to bunch the beam at S/sub 2/=2 cyclotron harmonic and a gyro-TWT output stage to extract energy from the bunched beam at S/sub 3/=2 cyclotron harmonic. Electronic coupling between neighboring stages is realized through ballistic beam bunching in the radiation-free drift space similar to what happens in a gyroklystron. Since S/sub 3/=S/sub 2/=2S/sub 1/, the device is a harmonic multiplying gyrotron amplifier with a scheme of 1-2-2. The clustered-cavity employed in the gyrotriotron is a group of TE/sub 03/ mode-selected cavities, which are closely adjacent and without any coupling between them. HFSS simulation of a sub-unit of such a mode selective clustered-cavity is given. This is a first use of cluster cavity in a gyrotron. The proof-of-principle gyrotriotron with Ku-band input, Ka-band TE/sub 04/ mode output, predicted peak output power of 500 kW and 5% bandwidth, has been fabricated and is being tested in the Harmonic Gyrotron Lab at University of Maryland.

Linear and nonlinear analysis of a gyrotron traveling wave amplifier with misaligned electron beam

This paper presents linear and self-consistent nonlinear theories to describe the beam-wave interaction in a gyrotron traveling wave amplifier (gyro-TWA) with a misaligned electron beam. A linear theory based on the linearized Vlasov equations is developed by using Laplace transforms. By setting appropriate initial values of the electron guiding center, the nonlinear theory without misalignment can be used to study the misalignment effect. The two theories are in good agreement in the small-signal region for the gyro-TWA. The effects of beam misalignment on the TE01 mode gyro-TWA operating at the fundamental are discussed and the corresponding physical mechanism is analyzed.

Potential advantages for millimeter-wave heating of powdered metals

Based on electromagnetic induction heating, an interaction model of microwaves with powdered metal has been established. The formulae of attenuation coefficient, heating rate and heating conversion efficiency are obtained and analyzed. The results of calculations show that millimeter waves may be able to overcome the obstacle caused by smaller skin depth and have strong advantages for the microwave heating of powdered metals. Experiments are done for comparison with present theory.

Effect of the lossy layer thickness of metal cylindrical waveguide wall on the propagation constant of electromagnetic modes

Based on the dispersion equation of electromagnetic mode, the propagation problem in a lossy cylindrical waveguide is studied. The analytic formula of propagation constant for any mode in the waveguide is presented, which includes the effect of the lossy layer thickness on the waveguide wall. The analysis with the analytic formula shows that the lossy layer thickness has great effect on the propagation constant when the thickness is 1.5 times smaller than the skin depth of good conductor (δ).

Investigation of the Failure Mechanism for an S-Band Pillbox Output Window Applied in High-Average-Power Klystrons

On the basis of the results of X-ray photoelectron spectroscopy, theoretical analyses, and numerical simulations, the failure mechanism of an S-band pillbox output window applied in a high-average-power klystron is discussed. The influence of the high-order cylindrical-guide modes on the microwave power loss, the direction of the power flow and the window disk cracking are investigated. The high-order cylindrical-guide TM11 mode existing on the surface of the window ceramic disk may cause the carbon film deposition and excessive radio frequency losses on the disk and lead to the breakdown of the window.