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Electron Devices, IEEE Transactions on

Issue 1 • Date Jan 2001

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Displaying Results 1 - 25 of 29
  • First pass TWT design success

    Page(s): 176 - 178
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    Making use of an ensemble of computer codes, Hughes Electron Dynamics (HED) has achieved first pass success in the design of slow wave circuits for several traveling wave tubes (TWTs) during the last year. By first pass design success we mean that when tested, the first device fabricated achieved the design goals for RF output power, basic efficiency, gain and phase shift. The design goals are derived from the predictions of a computer model, based on the exact dimensions of the TWT. The establishment of accurate computer models for the TWT slow wave circuit has enabled the optimization of a new design on the computer, eliminating the need for several experimental iterations in the development process. This accomplishment has enabled HED to significantly reduce the time required to develop new devices and demonstrate new design concepts View full abstract»

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  • Computer simulation of intermodulation distortion in traveling wave tube amplifiers

    Page(s): 178 - 180
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    The intermodulation performance of a helix TWT was computed using a large-signal disc model with two, three and eight correlated carriers and also using the program IMAL which models a generalized nonlinearity described by its single-carrier transfer characteristics. The results obtained by both methods showed good agreement. The intermodulation performance of a TWT for both correlated and uncorrelated carriers can therefore be predicted from its single-carrier transfer characteristics if they do not change significantly over the frequency range of interest View full abstract»

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  • Effect of geometric azimuthal asymmetries of PPM stack on electron beam characteristics [TWTs]

    Page(s): 38 - 44
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    A three-dimensional (3-D) beam optics model has been developed using the electromagnetic particle-in-cell (PIC) code MAFIA. The model includes an electron beam with initial transverse velocity distribution focused by a periodic permanent magnet (PPM) stack. All components of the model are simulated in three dimensions, allowing several azimuthally asymmetric traveling wave tube (TWT) characteristics to be investigated for the first time. These include C-magnets, shunts and magnet misalignment and their effects on electron beam behavior. The development of the model is presented and 3-D TWT electron beam characteristics are compared in the absence of and under the influence of the azimuthally asymmetric characteristics described View full abstract»

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  • The Hobetron-a high power vacuum electronic switch

    Page(s): 122 - 128
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    This paper describes a new high-power, hollow electron beam, current-regulating switch tube that we call the Hobetron. Experimental data on the Litton L-6026 Hobetron, an engineering prototype designed to stand off 125 kV dc and switch 200 amps, has demonstrated that Hobetron performance is in excellent agreement with computer predictions over the range of test. Further, the data confirmed that L-6026 switch power loss is less than 20% that of standard magnetron injection gun (MIG) switch tubes (for similar currents through each). Various potential Hobetron applications are presented throughout the paper. It is possible to include an additional electrode in the basic Hobetron configuration for even higher voltage standoff and switch current capability, and the paper presents an arrangement capable of standing off 500 kV dc and switching 500 amps. Simulations of a superpower “Hobetron-Plus” are presented, and the potential of this device as an efficient, 50 MW peak, relatively compact, VHF power amplifier for advanced heavy-particle (e.g., muon) colliders, is evaluated View full abstract»

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  • Development of a low voltage power booster TWT for a Q-band MMPM

    Page(s): 180 - 182
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    Compact millimeter wave amplifiers with output powers ranging from around 20 to 100 W are required for a number of important military and commercial applications. This paper describes the design of a miniature, low voltage, vacuum power booster TWT for a Q-band (40-45 GHz) millimeter wave power module (MMPM). At a design voltage of 7.7 kV and a maximum current of 120 mA, an output power goal of greater than 40 W of CW rf output power has been established for the Q-band TWT. Beam confinement is provided using an optimized samarium cobalt PPM stack. Circuit losses at millimeter wavelengths are minimized using a novel wire-wrapped, T-shaped BeO rod support structure. Output power is transmitted through a 0.051 cm, thick alumina ceramic output window. High overall device efficiency is achieved through the use of a 3 stage depressed collector. A recently completed engineering prototype produced 51 W of CW power at 41 GHz. Experimental overall device efficiency was 34.5%. These results will be described, as well as ongoing work to further improve overall device performance View full abstract»

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  • Numerical solution of fields in lossy structures using MAGY

    Page(s): 45 - 55
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    Lossy structures are used in vacuum electronic devices to control and suppress modes. Numerical simulation of the effect of these lossy structures is critical to the design and optimization of devices. The gyrotron simulation code MAGY makes use of the generalized telegraphist's equations in which the transverse structure of fields is represented as a sum of local modes of a metallic waveguide. If the wall is not a perfect conductor then sum over modes is not uniformly convergent. We have developed an algorithm to deal with this problem and allow for the simulation of structure with highly lossy walls. The theory and implementation of this algorithm are presented View full abstract»

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  • Analytical electrostatic model of silicon conical field emitters. I

    Page(s): 134 - 143
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    We present an analytical electrostatic model for a conical field emitter surrounded by a circular gate. The model is based on a radially symmetric orthonormal expansion of the potential throughout all space in the basis of Legendre functions of nonintegral degrees. The “bowling pin” model (BPM) makes it possible to calculate the total emission current and electron trajectories. The calculated values of the emitted current are in good agreement with the data. The value for the tip radius of curvature (ROC) obtained as the adjustable parameter in the model is in good agreement with that obtained from independent numerical modeling of the same devices View full abstract»

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  • Design of a Ka-band gyro-TWT for radar applications

    Page(s): 108 - 115
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    The design of a Ka-band gyrotron traveling wave tube (TWT) amplifier capable of operating over a wide range of peak powers and bandwidths is presented. The amplifier operates in the TE11 mode at the fundamental cyclotron harmonic. Instantaneous bandwidths in the range of 2.5 to 3.9 GHz (at 1 dB below saturation) with corresponding peak powers between 92.2 and 57.9 kW can be achieved by simply adjusting the mod-anode voltage of the electron gun. The corresponding gains range from 57.1 to 36.0 dB. The design performance is obtained with a high quality, 6 A, 70 kV electron beam generated with a double-anode magnetron injection gun. This wide range performance capability in the design is achieved via the use of the distributed loss approach in the interacting circuit, which also guarantees zero-drive stability. A diffractive loading scheme is employed in the lossy section of the circuit to ensure high average power operation of the amplifier View full abstract»

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  • Design of high-efficiency wide-bandwidth coupled-cavity traveling-wave tube phase velocity tapers with simulated annealing algorithms

    Page(s): 95 - 100
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    The output circuit section of a traveling-wave tube (TWT) routinely contains an RF phase velocity taper for the purpose of increasing RF output power and efficiency. By slowing the RF phase velocity in approximate synchronism with the decelerating electron beam bunches, the taper increases power transfer from the beam to the RF wave. Recently, the computational optimization technique of simulated annealing was shown to be very effective in the design of an RF phase velocity taper that significantly increased computed RF power and efficiency of a coupled-cavity TWT. In this paper, two new broadband simulated annealing algorithms are presented that optimize (1) minimum saturated efficiency over a frequency bandwidth and (2) simultaneous bandwidth and minimum efficiency over the frequency band with constant input power. The algorithms were incorporated into the NASA 2.5-dimensional (2.5-D) coupled-cavity TWT computer model and used to design optimal phase velocity tapers using a 59-64 GHz coupled-cavity TWT as a baseline model. Compared to the baseline taper design, the computational results of the first broadband algorithm showed an improvement of 73.9% in minimum saturated efficiency. The second broadband algorithm indicates an improvement of 272.7% in minimum RF efficiency with constant input power drive and an increase in simultaneous bandwidth of 0.5 GHz over that calculated for the baseline TWT View full abstract»

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  • COCA: a novel 3-D FE simulator for the design of TWT's multistage collectors

    Page(s): 24 - 31
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    In this paper, the simulator COCA, a novel fully three-dimensional (3-D) finite-element (FE) tool for the design of multistage depressed TWTs collectors is illustrated. COCA has been developed at the University of Catania under an ESA/ESTEC project. The complete simulator consists of three main modules: a fully 3-D deterministic/neural FE mesh generator, an FE Vlasov solver coupled with an electron trajectory tracer taking into account also external magnetic fields, and a postprocessing module for result restitution, including secondary electron emission effects. All the functions are interactively managed and executed by means of an especially developed user-friendly graphical user interface which controls all the various aspects of a simulation session. The results of a simulation test performed on an asymmetric collector are also reported showing excellent agreement with available measured data. The COCA simulator provides the user with flexible and effective tools to design, test, optimize, and verify innovative asymmetrical geometries for TWT collectors View full abstract»

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  • Analytical electrostatic model of silicon conical field emitters. II. Extension to devices with focusing electrode

    Page(s): 144 - 148
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    For pt. I see ibid., vol.48, no.1, p.134-43 (Jan. 2001). We extended the “bowling pin model” (BPM) presented in pt. I, to the case of double-gated conical field emitters. The model was used for trajectory calculations for both the single-gated and double-gated devices. Analysis also produced the governing relationship for the optimal operating voltages on the gate and focus electrodes of a double-gated emitter View full abstract»

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  • Control of IM3 distortion in helix TWTs by harmonic injection-an Eulerian hydrodynamical study

    Page(s): 62 - 67
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    Helix traveling-wave tube equations were formulated under Eulerian-fluid approximations, extending the nonlinearity up to the third-order. Closed-form solutions for the nonlinear equations were obtained by the method of Laplace transforms for the circuit electric field, which was then interpreted, for RF output power. The RF fundamental output power estimated by the present Eulerian theory was validated against that done by the Lagrangian analysis and the regime of agreement of the two theories was ascertained. Then within this range of validity were found the third-order intermodulation products at the frequencies 2f1-f2 and 2f2-f1, for the case of two-balanced signal inputs, one at the frequency f1 and the other at f2. The multisignal output power spectrum predicted by the two theories also showed a fairly close agreement. The role of the two additional second harmonic signals injected at the input, one at the frequency 2f1 and the other at 2f2, in controlling the third-order intermodulation products (distortion) was next studied by the simple Eulerian hydrodynamic analysis. By harmonic injection at the signal frequency 2f1 (2f2) alone, the intermodulation product at 2f1-f2 (2f2-f1) could be reduced but not at 2f2-f1 (2f1-f2). For the reduction of both the intermodulation products, the harmonic inputs at the frequencies 2f1 and 2f2, respectively, need to be simultaneously injected. In particular, the optimum values of the RF input power levels and phases of the second harmonic inputs relative to the corresponding fundamental inputs, which would result in a minimum in the third-order intermodulation distortion in the device, were found View full abstract»

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  • Advances in space TWT efficiencies

    Page(s): 174 - 176
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    Overall dc-to-rf conversion efficiency continues to be the single most significant figure of merit for commercial space traveling wave tube amplifiers (TWTAs). Improvements in TWTA efficiency immediately translate into potential revenue increases for satellite operators, since additional transponders can be carried on board the spacecraft for the same prime power and waste heat handling capacity. The revenue implications of increased efficiency have spurred TWT manufacturers to continue wringing out every possible increase in efficiency. By optimizing both rf circuit and collector designs, overall efficiencies >70% have now become routine. This paper will discuss the results of several experiments to improve TWT efficiency demonstrating how these impressive efficiencies may be achieved View full abstract»

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  • In-situ vacuum-sealed lateral FEAs with low turn-on voltage and high transconductance

    Page(s): 161 - 165
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    We have fabricated a new lateral field emitter array, in-situ vacuum-sealed, which exhibits a low turn on voltage and a high transconductance value without any additional vacuum sealing process. The vacuum-sealed lateral FEA (VLFEA) is encapsulated during the fabrication process, so that field emission characteristics can be measured without any additional vacuum environments. Experimental current-voltage (I-V) characteristics show that the anode current is field emission current obeying the linearity of the Fowler-Nordheim (F-N) plot. The experimental turn-on voltage of about 9 V is in good agreement with the extracted one from the F-N plot. In order to verify the integrity of the vacuum sealed micro-cavity, we have measured the anode current of the VLFEA both in a high vacuum chamber and in an atmospheric environment and found that the structure is well sealed. The anode currents as a function of gate voltage of the Mo-sealed VLFEA are analyzed and transconductance is extracted. The experimental results show that the VLFEA has superior field emission characteristics, such as low turn-on voltage and high transconductance, and does not require any additional troublesome vacuum sealing View full abstract»

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  • Computer simulation of ion trapping and detrapping in a PPM focused traveling wave tube

    Page(s): 56 - 61
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    This paper presents results from a time-dependent, electrostatic electron gun simulation code, simulating ion trapping and detrapping in a traveling wave tube (TWT) focused by periodic permanent magnets (PPM). The simulations described indicate that ion loss is primarily radial through the beam tunnel walls, rather than axial through the gun or collector. The electrostatic potential well formed by the electron beam is constantly being filled by ionization of a background neutral gas. This effect constitutes the primary ion loss mechanism. Filling of the potential well is made possible by loss of the low energy electrons produced by ionization (secondary electrons) through periodic nulls in the magnetic field View full abstract»

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  • Simulation of noise-power ratio with the large-signal code CHRISTINE

    Page(s): 32 - 37
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    This paper describes simulations of the noise-power ratio (NPR) for a helix traveling wave tube (TWT) performed with the large-signal, one-dimensional (1-D), multifrequency code CHRISTINE. The results obtained with this code are in better agreement with measured values than are the more traditional values calculated by power series. We conclude that NPR simulations with large-signal codes have the potential to shorten the design phase of TWTs by eliminating the need for repeated build-test cycles to meet a required NPR View full abstract»

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  • Micromachining technology for lateral field emission devices

    Page(s): 166 - 173
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    We demonstrate a range of novel applications of micromachining and microelectromechanical systems (MEMS) for achieving efficient and tunable field emission devices (FEDs). Arrays of lateral field emission tips are fabricated with submicron spacing utilizing deep reactive ion etch (DRIE). Current densities above 150 A/cm2 are achieved with over 150·106 tips/cm2. With sacrificial sidewall spacing, electrodes can be placed at arbitrarily close distances to reduce turn-on voltages. We further utilize MEMS actuators to laterally adjust electrode distances. To improve the integration capability of FEDs, we demonstrate batch bump-transfer of working lateral FEDs onto a quartz target substrate View full abstract»

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  • 94-GHz TWT for military radar applications

    Page(s): 72 - 73
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    For future military radar applications, high frequency, light-weight TWTs become more and more important. To cover this market, Thomson Tubes Electroniques GmbH several years ago started the development of a 94-GHz TWT. The goal of this program was a TWT (double comb delay line structure) in the 94-GHz frequency range with an instantaneous bandwidth greater than 500 MHz (tunable within 1 GHz) and an output peak power greater than 200 W in the center of the band (150 W over the band) for a duty cycle of max. 10%. The basic design and main test results of the 94-GHz TWT are the content of this paper View full abstract»

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  • Performance characteristics of an MSDC IOT amplifier

    Page(s): 116 - 121
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    The design and performance of an inductive output tube (IOT) based amplifier incorporating multistage depressed collector (MSDC) technology is summarized in this paper. The amplifier performance goal was to provide an enhanced efficiency rf amplifier for the UHF digital television broadcast market. The operational frequency of the amplifier is 470 to 820 MHz. The design emphasizes simplicity to minimize upgrade requirements for existing digital television transmitter designs and insure a low cost IOT. The enhanced efficiency IOT is based on an existing standard collector IOT capable of providing peak envelope powers of 60 kW. The collector design incorporates three elements with one element serving as a depression stage. The collector design curtails the reflection of spent beam electrons back to the IOT interaction gap and minimizes the generation of secondary electrons at critical collector surface locations. Testing emphasized the 8-VSB modulation scheme adopted by the ATSC for digital television broadcasting. Performance results indicate that the IOT electrical efficiency increased from 34% to 51% with the addition of MSDC collector when the amplifier is operated at 15 kW average rf power using the 8-VSB modulation scheme View full abstract»

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  • Mode selection in high power microwave sources

    Page(s): 129 - 133
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    In designing a microwave generator or an amplifier of enhanced power, we always risk encountering self-excitation of unwanted oscillations. To suppress parasitic oscillation modes, we may implement a selective rf absorber, organize a selective feedback, taper the rf structure profile to admit only the main operation mode into the wave-electron synchronism band, etc. At a proper switching-on scenario, the main operation mode of the device can suppress its rivals at the nonlinear interaction stage. This brief review is aimed to systematize numerous methods efficiently used to keep the coherence in high power vacuum devices based on the stimulated radiation by electron beams View full abstract»

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  • Microwave power module for space applications

    Page(s): 88 - 94
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    Microwave power modules (MPMs) were originally developed to satisfy requirements for extremely small, medium to high power amplifiers for a variety of conventional military and commercial applications. MPM technology has recently been enhanced to yield a proven space-qualified amplifier. This achievement is the result of a four-year development effort by Officine Galileo B.U. Spazio, Milan Plant (OG/MI, former FIAR S.p.A. Space Division). The space-qualified MPM was developed under an R&D contract from ESTEC and subsequently qualified using a dedicated engineering qualification model (EQM). The EQM produced 150 W at Ku-band and was manufactured with the support of the Italian Space Agency (ASI) and internal company funding. A brief description of the space qualified MPM is presented followed by the qualification test program and principal test results View full abstract»

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  • Silicide application on gated single-crystal, polycrystalline and amorphous silicon FEAs. II. Co silicide

    Page(s): 155 - 160
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    For pt. I see ibid., vol.48, no.1, p.149-54 (Jan. 2001). For enhancement and stabilization of electron emission, Co silicides were formed from Co, Co/Ti and Ti/Co layers on silicon FEAs. Since Ti prevents oxygen adsorption on the Co film during silicidation, uniform and smooth Co silicide layers can be obtained by depositing Co first and then Ti on silicon tips, followed by rapid annealing. Among Co silicide FEAs, Co silicide formed from Ti/Co bi-layers shows the lowest leakage current, the highest failure voltage over 152 V and the largest anode current over 1 mA at the gate voltage of 150 V. Compared with silicon field emitters, the silicide FEAs formed from Ti/Co layers exhibited a significant improvement in maximum emission current, emission current fluctuation and stability, and failure voltage View full abstract»

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  • 60-GHz space TWT to address future market

    Page(s): 68 - 71
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    The market situation of space traveling wave tubes (TWTs) over the last four years is reviewed. It is exemplified that space TWTs are not only the key components for the traditional frequency ranges in C- and Ku-band, but also for new satellite communication systems as digital audio broadcasting in the lower L- and S-band frequency range and the planned, new global multimedia systems. There, Thomson Tubes Electroniques GmbH (TTEG) has developed the new family of Ka band TWTs, which provide the large bandwidth and power requirements for high data rate transmission. TTEG is also developing 60-GHz TWTs as RF intersatellite-links for global satellite systems. The promising results of the 560 g lightweight, 25 W, broadband helix TWT are mainly reported and the requirements compared with those for a parallel 60 W 60-GHz interdigital line TWT development View full abstract»

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  • Tape helix perturbation including 3-D dielectrics for TWTs

    Page(s): 12 - 23
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    A perturbation technique described in a previous paper has been applied to the tape helix model of a traveling wave tube (TWT). The perturbation technique employs two solutions; the unperturbed solution is that for a helix in a conducting sleeve, suspended in vacuum, and the perturbed solution is with the above configuration, but with the introduction of dielectric support rods. Usually the perturbed solution is not known and is approximated by the homogeneous dielectric solution. Then in three-dimensional (3-D) fashion, the perturbation technique weights the dielectric with an energy-like term that is only evaluated within the discrete dielectric. Therefore, the model accounts for the distribution of dielectric material. Extending the perturbation to the tape helix, the current density is accurately portrayed in space. In all cases, the perturbed tape helix solution has a lower least square error in normalized phase velocity than the unperturbed tape helix solution. It had a lower error than the perturbed sheath helix solution of the previous paper, which in turn had a lower least square error than the Naval Research Laboratory's (NRL's) Small Signal Gain (SSG) Program. An initial discussion of the tape helix is presented and the calculated dispersion relation given. This solution incorporates a conducting backwall or shield with a homogeneous dielectric between it and the helix, using n=-6 to n=+6 space harmonics. Then the perturbation theory is applied, first for uniform support rods, and then to include notched rods. The resultant simulations produce phase velocity and coupling impedance data. Deviation from theory to experiment is reported by comparing the square root of the average sum of the squares difference, divided by an average phase velocity, between calculated phase velocities and a second order least squares fit of the measured data. Experimental data on the dispersion properties of four helices came from Northrop. The average error in phase velocity for four cases was 0.95%. For uniform rods the perturbation theory lowers the phase velocity, but doesn't significantly alter the dispersion. However, for notched rods, the perturbation theory raises the phase velocity and flattens the dispersion, in agreement with experiment. Computations can be performed in 1/2 min for a ten-frequency-step problem on a Pentium II processor View full abstract»

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  • Transient ion disturbances in traveling wave tubes

    Page(s): 82 - 87
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    It is well known that the presence of ions in the electron beam of a traveling wave tube (TWT) can lead to periodic variations in the output power, phase and the body (or helix) current. This has been referred to as ion noise or jitter. Recently, we have observed a different form of jitter, and while it is still observed as a small variation in the TWT output (typically <0.5 dB in power and 2° in phase), it is not periodic. We refer to this phenomenon as random jitter, since its random nature in time is a defining characteristic, Other characteristics include a relatively fast onset (~1 ms) and slow (~500 ms) recovery. It was found that random jitter was due to the spurious release of extremely small amounts of trapped gas inside the TWT. The source of the gas was identified and the problem was resolved. The observed level of fluctuations in power and phase had no effect on digital traffic and the small quantity of gas was found to have no measurable impact on cathode life View full abstract»

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Aims & Scope

IEEE Transactions on Electron Devices publishes original and significant contributions relating to the theory, modeling, design, performance and reliability of electron and ion integrated circuit devices and interconnects.

 

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Editor-in-Chief
John D. Cressler
School of Electrical and Computer Engineering
Georgia Institute of Technology