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  • 1
    Electronic Resource
    Electronic Resource
    Analysis and design of microwave amplifiers employing field-emitter arrays (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1485-1504 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analysis of the microwave ( f(approximately-greater-than)1 GHz) properties of field-emitter arrays (FEAs) and several representative medium power (10–100 W) microwave amplifiers employing FEAs is presented. The FEA analysis is limited to parallel-plate structures having discrete pointlike vertical emitter tips and gate apertures aligned to each tip. A transmission line analysis of wave propagation in this structure is presented and used to evaluate the geometries and materials needed for microwave operation. This analysis is used to investigate the performance capabilities and emitter requirements of both modulated-emission linear beam tubes and microdevices based on FEAs. Specific microtriode designs are used to investigate practical problems such as space charge and thermal effects. Competitive performance should be achievable in gated-emission linear beam tubes by using FEAs that perform at levels previously reported by several laboratories. Existing FEA technology (currents of 10 μA per emitter, transconductances of 1 μS per emitter, 1 μm oxide thickness, and 3 μm emitter spacing) is suitable for use in cavity klystrodes(r) at frequencies through 10 GHz, and in moderately bunched beam (bunch width of 180°), octave-bandwidth traveling-wave-tube applications through 3 GHz. Extending the operating frequency and/or reducing the bunch width will require a larger ratio of transconductance to current. Microtriodes operating at 10 GHz will benefit from a modified FEA structure and improved emitter performance.An extra acceleration electrode must be added above the gate aperture to alleviate problems due to space charge between the gate and collector, and the gate oxide thickness must be increased to at least 2 μm. A FEA incorporating these features and capable of producing 5 μS and 100 μA per emitter could generate 130 W from a 5-mm-wide device with 8.6 dB gain, 7% bandwidth, and 36% power added efficiency. To allow higher gain and wideband operation, the transconductance at a given current must be increased. A FEA capable of producing 5 μS at only 10 μA per emitter would result in a microtriode with more than 1 octave bandwidth, 45 W output power, 10 dB gain, and 34% power added efficiency. Anode-to-case temperature differences of less than 100 °C appear possible in this device if BeO is used as the dielectric.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353223
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  • 2
    Electronic Resource
    Electronic Resource
    Experimental studies of stability and amplification in four overmoded, two-cavity gyroklystrons operating at 9.87 GHz (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2423-2434 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The performance of four overmoded (TE011 circular), two-cavity gyroklystron amplifier tubes operating in X band is reported. A summary of the theoretical design procedure is presented, followed by a description of the experimental setup. The stability and amplification properties of the four gyroklystron tubes are subsequently described, each being modified in sequence to improve performance. The fourth tube produced 2.0–2.7 MW pulses at 9.87 GHz for 0.5–1.0 μs, and exhibited gains of 17–19 dB and efficiencies of 5%. The results were obtained using electron beams with voltages, currents, and computed beam alphas (v⊥/vz) of 407–425 kV, 115–135 A, and 0.8–1.0, respectively. The presence of instabilities in the gun downtaper and drift tube prevented operation at the design point (500 kV, 160 A, and alpha 1.5). The effects of varying input frequency, input power, and beam parameters (voltage, current, magnetic compression) on the amplifier operation are reported. Detailed descriptions of the instabilities observed in the gyroklystrons are presented, and the use of lossy dielectrics to suppress the instabilities is discussed. The amplifier experimental performance is compared with simulations. Improvement schemes are summarized and follow-up experiments are outlined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349394
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  • 3
    Electronic Resource
    Electronic Resource
    Studies of electronic noise in gyroklystrons : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2180-2185 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct measurements of phase noise in a four-cavity, 35 GHz gyroklystron producing 50 μs pulses of 175–210 kW output power with 50–53 dB saturated gain are presented. The measurements were performed at a 10.7 MHz frequency offset from the carrier, where the noise is expected to be dominated by shot noise and where the extrinsic noise from the electron gun's pulsed power supply is manageable. At an operating point with 70 kV beam voltage, 9 A beam current, and a beam velocity ratio of 1.3, a phase noise of −149±1 dBc/Hz was measured during the production of 180 kW output power at 50 dB gain. At a higher beam current of 10 A, the measured phase noise was −146±1 dBc/Hz during production of a 200 kW output power carrier with 53 dB gain. The directly measured phase noise levels were generally within 2–3 dB of the values expected on the basis of carrier-free noise temperature measurements. Overall, the measured gyroklystron noise levels are similar to those of conventional klystrons. Also presented are analytic calculations of the growth rates expected for electrostatic cyclotron instabilities in the region between the electron gun and the input cavity in a previous three-cavity gyroklystron. Very modest perpendicular velocity spreads (rms greater than 2%) are found to completely suppress such noise growth. This lack of significant noise growth above that of bare shot noise is in agreement with experimental results. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874038
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  • 4
    Electronic Resource
    Electronic Resource
    Experimental studies of bandwidth and power production in a three-cavity, 35 GHz gyroklystron amplifier (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 285-297 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The operating characteristics of a three-cavity, Ka-Band gyroklystron employing a large amount of stagger-tuning are reported. Particular attention is given to examining how the frequency response (peak power, bandwidth, and overall shape) is altered by changes in operating parameters. A peak power of 225 kW at 34.90 GHz, with a 2 μs pulse length, 32% efficiency, 30.3 dB saturated gain, and a 3 dB bandwidth of 0.82% (286 MHz) was obtained with a 70.2 kV, 10.0 A beam at a magnetic field of 13.07 kG. This operating point represents a compromise between the output power and the bandwidth. The operating magnetic field was found to have a dramatic influence on the power–bandwidth tradeoff; a lower field of 12.91 kG produced 245 kW with 0.63% bandwidth, while a higher field of 13.39 kG increased the bandwidth to 0.94% at a lower power of 200 kW. The results are in excellent agreement with large signal simulations.© 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873283
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  • 5
    Electronic Resource
    Electronic Resource
    Higher order mode excitations in gyro-amplifiers : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2488-2494 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In gyro-devices, a nonlinear output taper is often employed as the transition from the near cutoff radius of the interaction circuit to a much larger output waveguide. The tapers are usually designed to avoid passive mode conversion, and thus do not consider the effect of a bunched beam. However, recent simulations with the self-consistent MAGY code [Botton et al., IEEE Trans. Plasma Sci. 26, 882 (1998)] indicate that higher order mode interactions with the bunched electron beam can substantially compromise the mode purity of the rf output. The interaction in the taper region is traveling wave in nature, and is strongly dependent on the residual beam bunching characteristics resulting from the upstream operating mode interaction. An experiment has been performed to quantify the rf output mode content from a Ka-band gyroklystron. The agreement between salient theoretical and measured rf output characteristics confirms the existence of higher order mode excitation in output tapers as predicted by theory. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1348330
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  • 6
    Electronic Resource
    Electronic Resource
    Measurements of intrinsic shot noise in a 35 GHz gyroklystron (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2914-2925 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental measurements of electron beam shot noise in a 35 GHz, 225 kW, three-cavity gyroklystron have been obtained from both the input and output cavities. This intrinsic noise was studied in the absence of an applied carrier (i.e., at zero drive power). The spectrum of the noise emitted by the input cavity is found to have a Lorentzian shape, with peak noise power densities from the input cavity typically reaching 6.3×10−15 W/Hz (−112 dBm/Hz), and typical 3 dB bandwidths of 160 MHz. The output cavity noise spectrum is found to be equal to the input cavity noise spectrum multiplied by the measured linear frequency response of the gyroklystron. The measured noise levels at the input cavity are 0–5 dB lower than theoretical predictions for shot noise unaltered by collective effects. Furthermore, the input cavity noise power exhibits complex variations as a function of beam current, beam velocity ratio, and circuit magnetic field that are not predicted by present theory. Noise-to-carrier ratios expected in the input cavity during full power amplifier operation are inferred from the noise measurements and known values of drive power required to saturate the gyroklystron. The noise-to-carrier ratio, with typical values of −90 to −80 dBc, is found to be a strong function of the operating parameters. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873249
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  • 7
    Electronic Resource
    Electronic Resource
    Demonstration of a 10 kW average power 94 GHz gyroklystron amplifier (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 4405-4409 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The experimental demonstration of a high average power W-band (75–110 GHz) gyroklystron amplifier is reported. The gyroklystron has produced 118 AW peak output power and 29.5% electronic efficiency in the TE011 mode using a 66.7 kV, 6 A electron beam at 0.2% rf duty factor. At this operating point, the instantaneous full width at half-maximum (FWHM) bandwidth is 600 MHz. At 11% rf duty factor, the gyroklystron has produced up to 10.1 kW average power at 33% electronic efficiency with a 66 kV, 4.15 A electron beam. This represents world record performance for an amplifier at this frequency. At the 10.1 kW average power operating point, the FWHM bandwidth is 420 MHz. At higher magnetic fields and lower beam voltages, larger bandwidths can be achieved at the expense of peak and average output power. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873726
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  • 8
    Electronic Resource
    Electronic Resource
    Adjustable resonant cavity for measuring the complex permittivity of dielectric materials (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3207-3209 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An adjustable resonance cavity was developed to measure the complex permittivity of dielectric materials. The cavity has an inner diameter of 16.400 cm and an inner height of 2.54 cm. The aluminum stationary wall holder was positioned about 10.8 cm above the top of the cavity. It was fixed into place by three 1.27-cm-diam linear shafts. By suspending from the wall holder, the movable wall moved vertically by sliding on 1.27 cm bore-closed ball bushings. By turning a 1 in.-12 nut, the movable wall could be positioned so that the cavity height equaled the height of the sample. Therefore, this enables the measurement of the permittivity of samples with heights between 0.88 and 1.91 cm and radius between 1.27 and 3.18 cm. The complex permittivity of the sample was calculated based upon the sample dimensions, central frequency of TMono modes, and Q factor of the resonance curve using an exact solution. The complex permittivity was measured at the three lowest modes, where the frequency span is 1–4 GHz. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1304865
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  • 9
    Electronic Resource
    Electronic Resource
    High power operation of first and second harmonic gyrotwystrons (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 550-559 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the first experimental operation of overmoded first and second harmonic gyrotwystron amplifier configurations. Both devices utilize a single cavity which is driven near 9.87 GHz in the TE011 mode, heavily attenuated drift tubes, and long tapered output waveguide sections. A magnetron injection gun produces a 460 kV, 245 A beam with a maximum average perpendicular-to-parallel velocity ratio approximately equal to one. The axial magnetic field profile is sharply tapered in the output section. Peak powers above 21 MW are achieved in 1 μs pulses with an efficiency exceeding 22% and a large signal gain near 24 dB in the first harmonic tube. The second harmonic tube achieves nearly 12 MW of the peak power with an efficiency of 11% and a gain above 21 dB. First harmonic amplifier performance is limited principally by competition from a fundamental mode output waveguide interaction; the second harmonic tube is limited by both travelling wave output modes and by a down-taper oscillation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360639
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  • 10
    Electronic Resource
    Electronic Resource
    Operation of a K-band second harmonic coaxial gyroklystron (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4393-4398 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amplification studies of a two-cavity second harmonic gyroklystron with a coaxial input cavity and drift tube are reported. The inner conductor is supported by tungsten pins which intercept the beam, and it utilizes lossy dielectric rings to enhance mode suppression. A double-anode magnetron injection gun produces a 440 kV, 200–268 A, 1 μs beam with an average perpendicular-to-parallel velocity ratio near one. The TE011 input cavity is driven near 9.886 GHz and the TE021 output cavity resonates near 19.772 GHz. Peak powers near 30 MW have been achieved, although more easily reproducible peak powers hover closer to 20 MW. While stability is improved over previous devices, beam interception reduces the accessible range in parameter space and thus degrades amplifier performance. Pin erosion is also evident and qualitatively agrees well with theoretical predictions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358448
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