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B.n. Basu - One of the best experts on this subject based on the ideXlab platform.

  • Exploration of a double-tapered disc-loaded circular waveguide for a wideband gyro-TWT
    IEEE Electron Device Letters, 2006
    Co-Authors: Vishal Kesari, Pradip Kumar Jain, B.n. Basu
    Abstract:

    The analysis of a disc-loaded circular waveguide interaction structure of a gyro-traveling-wave-tube (gyro-TWT) considering standing and propagating mode harmonics in the disc-occupied and disc-free regions, respectively, gave the beam-absent dispersion relation of the waveguide. The axial phase propagation constant predicted by the dispersion relation was substituted into the gyro-TWT gain-equation, the latter obtainable from the beam-present dispersion relation of the device. A method of double-tapering the structure dimensions was proposed that consists in tapering the disc-Hole Radius to distribute the midband frequency of amplification over a wide range of frequencies, and simultaneously tapering the waveguide-wall Radius to compensate for gain reduction at band edges due to disc-Hole Radius tapering. The method has demonstrated wide device bandwidths at relatively large gain values.

  • Modelling of axially periodic circular waveguide with combined dielectric and metal loading
    Journal of Physics D, 2005
    Co-Authors: Vishal Kesari, Pradip Kumar Jain, B.n. Basu
    Abstract:

    A previously developed field matching technique for the analysis of a metal disc-loaded circular waveguide, excited in a non-azimuthally varying transverse electric (TE) mode, was used to explore the advantage of the presence of a dielectric in controlling its dispersion characteristics for widening the bandwidth of a gyro-travelling-wave tube (gyro-TWT). The modelled structure, consisting of an axial dielectric insert and dielectric discs alternately placed between metal discs, was analysed considering the propagating and stationary waves in the disc-free and disc-occupied regions, respectively. While the axial dielectric insert gave no specific advantage with respect to dispersion control, the dielectric disc axial thickness, permittivity and periodicity and disc-Hole Radius quite effectively shaped the structure dispersion. In controlling the structure dispersion, the disc-Hole Radius, which was not as effective as the disc-periodicity in a conventional metal disc-loaded waveguide, became more effective, though the disc periodicity did not enjoy any additional advantage. The thickness or permittivity of dielectric discs controlled the passband frequencies and hence helped attain operating frequencies of a gyro-TWT. The passband of the lower and higher order modes remaining unchanged by a suitable choice of the structure parameters, a higher order mode, for instance the TE02 mode, gave a better wideband potential than the TE01 mode.

  • Analysis of a Disc-Loaded Circular Waveguide for Interaction Impedance of a Gyrotron Amplifier
    International Journal of Infrared and Millimeter Waves, 2005
    Co-Authors: Vishal Kesari, P. K. Jain, B.n. Basu
    Abstract:

    A rigorous electromagnetic analysis of a circular waveguide loaded with axially periodic annular discs was developed in the fast-wave regime, considering finite axial disc thickness and taking into account the effect of higher order space harmonics in the disc-free region and higher order modal harmonics in the disc-occupied region of the structure. The quality of the disc-loaded circular waveguide was evaluated with respect to its azimuthal interaction impedance that has relevance to the gain of a gyrotron millimeter-wave amplifier (gyro-traveling-wave tube) in which such a loaded waveguide finds application as a wideband interaction structure. The results of electromagnetic analysis of the structure with respect to both the dispersion and azimuthal interaction impedance characteristics were validated against the commercially available code: high frequency structure simulator (HFSS). The analysis predicts that the value of the interaction impedance at a given frequency decreases with the increase of the disc Hole Radius and disc periodicity. The change of the axial disc thickness does not significantly change the value of the interaction impedance though it shifts the frequency range over which appreciable interaction impedance is obtained. Out of the three disc parameters, namely the disc Hole Radius, thickness and periodicity, the lattermost is most effective in controlling the value of the azimuthal interaction impedance. However, the passband of frequencies and the center frequency of the passband both decrease with the increase of the disc periodicity. Moreover, the disc periodicity that provides large azimuthal interaction impedance would in general be different from that giving the desired dispersion shape for wideband interaction in a gyro-TWT, suggesting a trade-off in the value of the disc periodicity to be chosen.

J.-q. Liang - One of the best experts on this subject based on the ideXlab platform.

  • Model calculation for enhancement factor of a gated field emission nanotube
    Journal of Applied Physics, 2007
    Co-Authors: L. Y. Zeng, W. B. Wang, J.-q. Liang
    Abstract:

    The field enhancement factor of gated nanotube with opened top was analytically calculated by the electrostatic method. The effect of geometrical parameters of the device on their field enhancement factor was investigated, including the gate-Hole Radius, gate-anode distance, and nanotube Radius. The theoretical analysis shows that the enhancement factor increases greatly with the decrease of gate-Hole Radius. However, if the gate voltage is zero, the factor increases with the increase of gate-Hole Radius, and finally reaches a constant, which increases with the increase of nanotube length L. The enhancement factor β gets larger when the nanotube Radius gets smaller. As the gate-anode distance d2 is finite, the β will decrease with the increase of d2. If the d2 is infinite, the effect of gate-anode distance on β can be ignored. All the results of theoretical calculation can provide useful information in the fabrication and design of the gated nanotube cold cathode for field emission display panels and othe...

  • Model calculation for enhancement factor of a gated field emission nanotube
    Journal of Applied Physics, 2007
    Co-Authors: D. Lei, L. Y. Zeng, W. B. Wang, J.-q. Liang
    Abstract:

    The field enhancement factor of gated nanotube with opened top was analytically calculated by the electrostatic method. The effect of geometrical parameters of the device on their field enhancement factor was investigated, including the gate-Hole Radius, gate-anode distance, and nanotube Radius. The theoretical analysis shows that the enhancement factor increases greatly with the decrease of gate-Hole Radius. However, if the gate voltage is zero, the factor increases with the increase of gate-Hole Radius, and finally reaches a constant, which increases with the increase of nanotube length L. The enhancement factor beta gets larger when the nanotube Radius gets smaller. As the gate-anode distance d(2) is finite, the beta will decrease with the increase of d(2). If the d(2) is infinite, the effect of gate-anode distance on beta can be ignored. All the results of theoretical calculation can provide useful information in the fabrication and design of the gated nanotube cold cathode for field emission display panels and other nanoscale triode devices. (c) 2007 American Institute of Physics.

Soonhong Kwon - One of the best experts on this subject based on the ideXlab platform.

  • Elimination of cross-talk in waveguide intersections of triangular lattice photonic crystals.
    Optics Express, 2008
    Co-Authors: Soonhong Kwon, Martin Kamp, Alfred Forchel
    Abstract:

    We design an intersection for crossing waveguides in triangular lattice photonic crystals with cross-talk smaller than 10−5. The cross-talk to the transverse waveguides is suppressed by symmetry mismatch between the cavity mode and the waveguide mode or by the mode-gap effect induced by air Hole Radius modulation of the waveguides. The transmission behavior of the crossing waveguides are illustrated by numerical simulations through finite difference time domain method.

  • ultrahigh q photonic crystal cavity created by modulating air Hole Radius of a waveguide
    Optics Express, 2008
    Co-Authors: Soonhong Kwon, T Sunner, Martin Kamp, A Forchel
    Abstract:

    We propose an ultrahigh quality factor (Q) photonic crystal slab cavity created by the local modulation of the air Hole Radius in the waveguide. In the cavity, photons are confined between two mirror regions with larger air Holes and the lifetime of photons is greatly enhanced by introducing tapered regions with linearly increasing air Hole radii. Q and mode volume are investigated for the cavities with various lengths and air Hole size offsets of the tapered region with linearly increasing air Hole radii by three-dimensional finite-difference time-domain method. The behaviors are analyzed by the mode patterns in real space and wavevector space. We obtain a numerical Q up to 8.8×107 for a mode volume of 1.6 (λ/n)3. Concerning the waveguide coupling, the cavity shows 80% coupling efficiency while keeping Q higher than 106.

A Forchel - One of the best experts on this subject based on the ideXlab platform.

  • ultrahigh q photonic crystal cavity created by modulating air Hole Radius of a waveguide
    Optics Express, 2008
    Co-Authors: Soonhong Kwon, T Sunner, Martin Kamp, A Forchel
    Abstract:

    We propose an ultrahigh quality factor (Q) photonic crystal slab cavity created by the local modulation of the air Hole Radius in the waveguide. In the cavity, photons are confined between two mirror regions with larger air Holes and the lifetime of photons is greatly enhanced by introducing tapered regions with linearly increasing air Hole radii. Q and mode volume are investigated for the cavities with various lengths and air Hole size offsets of the tapered region with linearly increasing air Hole radii by three-dimensional finite-difference time-domain method. The behaviors are analyzed by the mode patterns in real space and wavevector space. We obtain a numerical Q up to 8.8×107 for a mode volume of 1.6 (λ/n)3. Concerning the waveguide coupling, the cavity shows 80% coupling efficiency while keeping Q higher than 106.

Vishal Kesari - One of the best experts on this subject based on the ideXlab platform.

  • Exploration of a double-tapered disc-loaded circular waveguide for a wideband gyro-TWT
    IEEE Electron Device Letters, 2006
    Co-Authors: Vishal Kesari, Pradip Kumar Jain, B.n. Basu
    Abstract:

    The analysis of a disc-loaded circular waveguide interaction structure of a gyro-traveling-wave-tube (gyro-TWT) considering standing and propagating mode harmonics in the disc-occupied and disc-free regions, respectively, gave the beam-absent dispersion relation of the waveguide. The axial phase propagation constant predicted by the dispersion relation was substituted into the gyro-TWT gain-equation, the latter obtainable from the beam-present dispersion relation of the device. A method of double-tapering the structure dimensions was proposed that consists in tapering the disc-Hole Radius to distribute the midband frequency of amplification over a wide range of frequencies, and simultaneously tapering the waveguide-wall Radius to compensate for gain reduction at band edges due to disc-Hole Radius tapering. The method has demonstrated wide device bandwidths at relatively large gain values.

  • Modelling of axially periodic circular waveguide with combined dielectric and metal loading
    Journal of Physics D, 2005
    Co-Authors: Vishal Kesari, Pradip Kumar Jain, B.n. Basu
    Abstract:

    A previously developed field matching technique for the analysis of a metal disc-loaded circular waveguide, excited in a non-azimuthally varying transverse electric (TE) mode, was used to explore the advantage of the presence of a dielectric in controlling its dispersion characteristics for widening the bandwidth of a gyro-travelling-wave tube (gyro-TWT). The modelled structure, consisting of an axial dielectric insert and dielectric discs alternately placed between metal discs, was analysed considering the propagating and stationary waves in the disc-free and disc-occupied regions, respectively. While the axial dielectric insert gave no specific advantage with respect to dispersion control, the dielectric disc axial thickness, permittivity and periodicity and disc-Hole Radius quite effectively shaped the structure dispersion. In controlling the structure dispersion, the disc-Hole Radius, which was not as effective as the disc-periodicity in a conventional metal disc-loaded waveguide, became more effective, though the disc periodicity did not enjoy any additional advantage. The thickness or permittivity of dielectric discs controlled the passband frequencies and hence helped attain operating frequencies of a gyro-TWT. The passband of the lower and higher order modes remaining unchanged by a suitable choice of the structure parameters, a higher order mode, for instance the TE02 mode, gave a better wideband potential than the TE01 mode.

  • Analysis of a Disc-Loaded Circular Waveguide for Interaction Impedance of a Gyrotron Amplifier
    International Journal of Infrared and Millimeter Waves, 2005
    Co-Authors: Vishal Kesari, P. K. Jain, B.n. Basu
    Abstract:

    A rigorous electromagnetic analysis of a circular waveguide loaded with axially periodic annular discs was developed in the fast-wave regime, considering finite axial disc thickness and taking into account the effect of higher order space harmonics in the disc-free region and higher order modal harmonics in the disc-occupied region of the structure. The quality of the disc-loaded circular waveguide was evaluated with respect to its azimuthal interaction impedance that has relevance to the gain of a gyrotron millimeter-wave amplifier (gyro-traveling-wave tube) in which such a loaded waveguide finds application as a wideband interaction structure. The results of electromagnetic analysis of the structure with respect to both the dispersion and azimuthal interaction impedance characteristics were validated against the commercially available code: high frequency structure simulator (HFSS). The analysis predicts that the value of the interaction impedance at a given frequency decreases with the increase of the disc Hole Radius and disc periodicity. The change of the axial disc thickness does not significantly change the value of the interaction impedance though it shifts the frequency range over which appreciable interaction impedance is obtained. Out of the three disc parameters, namely the disc Hole Radius, thickness and periodicity, the lattermost is most effective in controlling the value of the azimuthal interaction impedance. However, the passband of frequencies and the center frequency of the passband both decrease with the increase of the disc periodicity. Moreover, the disc periodicity that provides large azimuthal interaction impedance would in general be different from that giving the desired dispersion shape for wideband interaction in a gyro-TWT, suggesting a trade-off in the value of the disc periodicity to be chosen.