Small-signal Region Research Articles

Study of the Mechanism and Suppression of Group Delay Distortion of a Traveling-Wave Tube Using Eulerian Hydrodynamic Analysis

In this paper, a simplified Eulerian nonlinear beam-wave interaction (BWI) theory of a helix traveling-wave tube (TWT) is developed. Derived from this model, analytic solutions are first obtained by the method of successive approximation. Then, the linear analytic solution of group delay distortion (GDD) is obtained. Subsequently, the mechanism of group delay is studied. It is found that the main mechanism of GDD is the propagation time difference between the wave group and electron beam throughout the BWI region. Furthermore, a series of group delay suppression schemes is discussed by using the mechanism. Finally, the Eulerian formation and the suppression schemes are validated by an in-house code based on the Lagrangian theory. Results show that the analytic solutions of Eulerian model and GDD agree well with the Lagrangian theory in small-signal region. In addition, the suppression schemes are applied to a high-efficiency Ku-band space TWT. The GDD is greatly reduced by approximately 50% with a slightly drop of output power.

Linear and Nonlinear Analyses of a 0.34-THz Confocal Waveguide Gyro-TWT

In this paper, the dispersion relation of the beam wave interaction of the confocal waveguide gyrotron-traveling-wave tube (confocal gyro-TWT) is derived from kinetic theory for the first time; according to this dispersion relation, we can make the linear analysis of confocal gyro-TWT as well as the cylindrical waveguide gyro-TWT. At the same time, a numerical code based on the self-consistent nonlinear theory is written to simulate the behavior of electron beam and electromagnetic wave during beam wave interaction. When neglecting the spread of velocity and guiding center, the gain and growth rate calculated by the nonlinear theory code makes great agreement with that of linear theory in the small-signal region.

An Optimized Segmented Quasi-Memoryless Nonlinear Behavioral Modeling Approach for RF Power Amplifiers

This paper presents an optimized segmented modeling approach using a new quasi-memoryless (QM) behavioral model (BM) that allows for RF power amplifier (RF PA) modeling over a range of different solid state PA technologies. The presented model is a combination of an existing semiphysical amplitude-modulation-to-amplitude-modulation (AM/AM) memoryless BM, which correctly predicts third-order intermodulation distortion (3rd IMD) response in the small signal region, with the newly proposed amplitude-modulation-to-phase-modulation (AM/PM) model derived from the existing AM/AM model. Using the segmentation and optimization methods, performance comparisons with this new model are presented, showing normalized mean squared error AM/PM improvements up to 20 dB, as well as over 5-dB improvement in predicting the 3rd IMD using the proposed model. Comparisons against other well-known QM BMs are conducted using measured data as well as with data presented in the literature. The effects of these improvements on linearizer performance are also evaluated. The model significantly improves system-level modeling by allowing designers to accurately predict system performance using various RF PA devices over a range of technologies, based on data available through manufacturers’ data or simple tests.

Modal analysis based equivalent circuit model and its verification for a single cMUT cell

This paper presents the lumped equivalent circuit model and its verification of both transmission and reception properties of a single cell capacitive micromachined ultrasonic transducer (cMUT), which is operating in a non-collapse small signal region. The derivation of this equivalent circuit model is based on the modal analysis techniques, harmonic modes are included by using the mode superposition method; and thus a wide frequency range response of the cMUT cell can be simulated by our equivalent circuit model. The importance of the cross modal coupling between different eigenmodes of a cMUT cell is discussed by us for the first time. In this paper the development of this model is only illustrated by a single circular cMUT cell under a uniform excitation. Extension of this model and corresponding results under a more generalized excitation will be presented in our upcoming publication (Mao et al 2016 Proc. IEEE Int. Ultrasonics Symp.). This model is verified by both finite element method (FEM) simulation and experimental characterizations. Results predicted by our model are in a good agreement with the FEM simulation results, and this works for a single cMUT cell operated in either transmission or reception. Results obtained from the model also rather match the experimental results of the cMUT cell. This equivalent circuit model provides an easy and precise way to rapidly predict the behaviors of cMUT cells.

Polarized fiber optical parametric amplification in randomly birefringent fibers.

A comprehensive theoretical model to investigate phase matching in degenerate polarized fiber optical parametric amplifiers (FOPAs) in randomly birefringent fibers is developed. We show that in the small signal region, simulation results from the proposed model agree well with the experimental results. It was also shown that four waves mixing (FWM) effect could compensate polarization mode dispersion (PMD) induced phase mismatch. Similar to counter-propagating fiber Raman amplifiers (FRAs), the degree of polarization of FOPAs approaches unity exponentially with the gain but at a larger rate 1/Γ. Thus larger polarization-pulling can be achieved in FOPAs than the counter-propagating FRAs for the same gain.

Optimization of Raman-Assisted Fiber Optical Parametric Amplifier Gain

We studied the gain of Raman-assisted fiber optical parametric amplifiers (RA-FOPAs) both theoretically and experimentally. We investigated the relationship between the overall gain and different combinations of Raman and parametric pump powers using contour maps. We derived a normalized phase-matched model to determine the general behavior the peak gains of RA-FOPAs operating in the small signal region. The contour maps of the combined gain enhancement can be used to optimize both indirect and direct Raman gain of the signal/idler in RA-FOPAs. We showed that, in a given fiber, it is possible to optimize the Raman and parametric pump powers in RA-FOPAs for high gain and high efficiency.

Linear and nonlinear theories of a large-orbit gyrotron traveling wave amplifier

The linear and nonlinear theories of large-orbit gyrotron traveling wave amplifiers (gyro-TWAs) have been developed based on the corresponding theories of small-orbit gyro-TWAs. The linear theory is in good agreement with the nonlinear theory in the small signal region of large-orbit gyro-TWAs. The phenomenon that most electrons move toward the axis of interaction circuit during the beam-wave interaction is observed and its potential effect on the design of large-orbit coaxial gyro-TWAs is emphasized.

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.

A dual bias-feed circuit design for SiGe HBT low-noise linear amplifier

An SiGe HBT low-noise amplifier (LNA) with a novel diode/resistor dual base bias-feed circuit is described. The dual bias-feed circuit extends P1 dB without degradation of the noise figure (NF). In the small-signal region, a conventional resistor bias-feed circuit is a dominant base current source and, in the large-signal region, the diode turns on and the diode bias-feed circuit supplies the base current like a voltage source, which allows higher output power and linearity. In this paper, the operation principle of the dual bias-feed circuit is explained by using a virtual current source model, which indicates the increase of base current of the HBT in a large-signal region. The design method is also described for the idle current of the diode bias-feed circuit in a small-signal region from the points-of-view of NF and P1 dB. The effectiveness of the dual bias-feed circuit is evaluated by simulation and measurement. The fabricated 2-GHz-band dual bias-feed LNA has the P1 dB improvement of 5 dB and no degradation NF compared with the conventional resistor bias-feed LNA.

The clouds of Jupiter: Results of the Galileo Jupiter Mission Probe Nephelometer Experiment

The results of the nephelometer experiment conducted aboard the probe of the Galileo mission to Jupiter are presented. The tenuous clouds and sparse particulate matter in the relatively particle‐free 5‐μm “hot spot” region of the probe's descent were documented from about 0.46 bar to about 12 bars. Three regions of apparent coherent structure were noted, in addition to many indications of extremely small particle concentrations along the descent path. From the first valid measurement at about 0.46 bar down to about 0.55 bar, a feeble decaying lower portion of a cloud, corresponding with the predicted ammonia particle cloud, was encountered. A denser, but still very modest, particle structure was present in the pressure regime extending from about 0.76 bar to a distinctive base at 1.34 bars and is compatible with the expected ammonium hydrosulfide cloud. No massive water cloud was encountered, although below the second structure, a small, vertically thin layer at about 1.65 bars may be detached from the cloud above, but may also be water condensation, compatible with reported measurements of water abundance from other Galileo Mission experiments. A third small signal region, extending from about 1.9 to 4.5 bars, exhibited quite weak but still distinctive structure and, although the identification of the light scatterers in this region is uncertain, may also be a water cloud, perhaps associated with lateral atmospheric motion and/or reduced to a small mass density by atmospheric subsidence or other causes. Rough descriptions of the particle size distributions and cloud properties in these regions have been derived, although they may be imprecise because of the small signals and experimental difficulties. These descriptions document the small number densities of particles, the moderate particle sizes, generally in the slightly submicron to few micron range, and the resulting small optical depths, mass densities due to particles, column particle number loading, and column mass loading in the atmosphere encountered by the Galileo probe during its descent.

Enhanced Raman conversion by a two-longitudinal-mode beam in the para-hydrogen Raman laser

Using a longitudinally mode-controlled transversely excited atmospheric CO2 laser, we studied the conversion characteristics of single-, two-, and multimode pump pulses in a para-H2 Raman laser. In the small signal region, two- and multimode pump pulses showed higher Raman conversion efficiencies. In the saturation region, however, output energies pumped with single- and two-mode pulses exceeded those pumped with multimode pulses. Consequently, the two-mode pumping was the most efficient within the limit of pump energies used in the experiment. The results are explained in relation to the mode-mixing effect for the correlated pump and Stokes beams.

EFFICIENCY ENHANCEMENT OF FAR INFRARED FREE ELECTRON LASER BY USING A REVERSE TAPERING WAVEGUIDE

In the high efficiency and small signal region, we investigate theoretically the efficiency enhancement mechanism of far infrared free electron laser (FIR-FEL) with a reverse tapering waveguide. The numerical simulatiion with single particle model suggests that this kind of waveguide whose gap is gradually narrow along z axis substantially heightens the FIR-FEL efficiency.

Reflection insensitive erbium-doped fiber amplifier

It is experimentally and theoretically examined how the insertion of an isolator within the erbium-doped fiber influences the sensitivity of the fiber amplifier to external reflections. We examined the EDFA in various regions of saturation, and compared the configuration with the isolator to the traditional configuration without an isolator. The most significant improvements were found in the small-signal region, where the requirements to reflections may be relaxed by as much as 13 dB. This, together with an improved gain and noise figure, makes the configuration with the isolator very attractive for preamplifier applications. >

A highly sensitive on-chip charge detector for CCD area image sensor

A novel on-chip charge detector for charge-coupled-device (CCD) image sensor applications was fabricated and evaluated. The device, called the double-gate floating surface detector, achieves a charge/voltage conversion gain of 220 mu V/electron, a noise equivalent electron of 0.5 electrons r.m.s. and a dynamic range of 79 dB over 3.58-MHz video bandwidth at room temperature. In the small-signal region under 20 electrons, which is the photon counting region for highly sensitive imaging devices, the device was evaluated by observing the discrete voltage levels corresponding to the number of signal electrons on an oscilloscope. This evaluation confirmed that the high charge voltage conversion gain is also maintained in this region.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Bridge measuring method of active impedance of crystal oscillator circuits

AbstractCrystal oscillator circuits have been used widely in such electronic equipment as communication devices and measurement instruments. However, until the crystal is connected, usually it is uncertain if the circuit oscillates or it is difficult to determine how one adjusts the circuit for a desired oscillation frequency. With a view to alleviating these situations and improving the design method for the crystal oscillator circuits, a method is developed for accurately measuring with a bridge the two‐terminal impedance (equivalent series capacitance and negative resistance) of the active circuit seen from the connecting terminal of the crystal. A bridge measurement method for the small‐signal negative resistance related to the starting characteristics of the oscillator is discussed. In conjunction with the bridge measurement developed earlier for large signal operations under oscillation, a complete bridge measurement has become possible from the small signal region to the large signal region. The present bridge measurement method is useful in providing a basic specification for the active circuit side for a given crystal. It is also shown that the present bridge method is useful for evaluation of accuracy of other measurement instruments such as impedance analyzers.

High-efficiency extraction study of an electron beam pumped ArF laser amplifier with an atmospheric-pressure Ar-rich mixture

The characteristics of an electron beam excited ArF laser amplifier were investigated from the small-signal region to the strongly saturated region (≥10 MW/cm2) as a function of Ar concentration. A single-pass (L=50 cm) amplifier experiment was performed with atmospheric Ar/F2 and Ne/Ar/F2 gas mixtures pumped by an intense electron beam (1.3 MV, 90 kA, 65 ns full width half-maximum). The extracted intensity (output intensity minus input intensity) from this single-pass amplifier was maximized at input intensities ranging from 6.7 to 9.5 MW/cm2. The power efficiencies obtained were 13, 14.4, and 15.7%, and the extraction efficiencies were 65, 59.7, and 59.4% for Ar concentrations of 40, 70, and 99.6%, respectively. The amplifier parameters (small-signal gain g0, nonsaturable absorption coefficient α, and saturated intensity Is) were estimated for each mixture using a Rigrod analysis [J. Appl. Phys. 36, 2487 (1965)].

電子ビーム加工における高速ビーム偏向の研究

A frequency band required for an oscillation technique on an electron beam welding was discussed by analyzing vibration frequencies of molten metal. Lower limits of beam scanning velocity not melting surfaces of work-pieces were also discussed by calculating temperature rise. A high-speed beam deflecting device to satisfy above conditions was developed and some applications of high-speed beam deflection were studied.The conclusions obtained are summarized as follows:(1) The vibration frequencies of the molten metal are less than 10 kHz and a beam oscillation with higher frequencies than 10 kHz is necessary to control distribution of an input power to a work-piece regardless of molten metal vibration.(2) A beam scanning velocity of more than 10000 m/min is required not to melt a steel surface for a beam power of 10 kW(3) A cutoff frequency of 60 kHz (-3dB) in small signal region and a maximum scanning velocity of 23000 m/min (deflection distance 300 nun) are realized using a deflecting device newly developed.(4) The high-speed deflection technique is very effective for the new-field of electron beam application such as marking, patterning, simultaneous multi-beam welding, surface hardening, and so forth.

Two-element free-electron lasers

The interaction between the electrons and the radiation in a free-electron laser leads to a shift and a spread of the electron velocity distribution. The electron dynamics of a two-element system are studied in the small signal region. It is found that the efficiency and gain can be increased through introduction of an adjustable drift distance between two identical wigglers.

New Instability Concept in Avalanche Diode Oscillation

The essential nature of the avalanche diode oscillator is discussed on the basis of the Volterra's ecological system utilizing a nonlinear competition equation which has an oscillatory solution. The solution describes the IMPATT diode mode in a small-signal region, and in a large-signal region, transforms into the TRAPATT diode mode. The characteristics of the two modes are treated in such a way to suggest a unified fundamental concept. The importance of the nonlinear nature of the avalanche process is stressed.

Analysis of nonlinear systems with multiple inputs

Analytical modeling of communication receivers to account for their nonlinear response to multiple input signals is discussed. The method is based on the application of the Wiener-Volterra analysis of nonlinear functionals. The derived analytical relations were embodied in a computer program which provides nonlinear transfer functions of large circuits specified by their parameters. This method was applied to the prediction of behavior of communication receivers in the presence of interference. Examples illustrate the method and demonstrate its validity in the small-signal region.