An active circulator-gyrotron traveling-wave amplifier

A recent experiment demonstrated that wide-band amplification of millimeter waves is feasible by using a tapered gyrotron traveling-wave amplifier (gyro-TWA) of the reflection type. In this paper, we show that the difficult problem of input/output coupling in such a reflection amplifier may be solved simply by the use of an almost square waveguide, with or without a dielectric lining. An input signal in the form of TEmin{01}max_{square} mode, say, is injected from the downstream of the electron beam of the gyro-TWA. It propagates upstream and is reflected by the constriction of the tapered waveguide. By a judicious choice of the waveguide dimensions and of the magnetic field profile, we find that it is possible for the reflected wave to be strongly amplified in the TEmin{10}max_{square} mode, which has a polarization orthogonal to the input mode, thereby permittting easy separation of the input and the output signal. This novel device thus performs the dual function of an amplifier and of a circulator with wide bandwidth and good power handling capabilities at millimeter wavelengths. This optimism is based on the numerical studies presented in this paper. Furthermore, the simultaneous presence of the TEmin{01}max_{square} and TEmin{10}max_{square} modes is found to strengthen the beam-circuit interaction. All of the known advantages of the reflection gyro-TWA, such as the lack of the 9-dB launching loss and the insensitivity to the beam velocity spread, are expected to be preserved in this device. The effects of reflection from the load is considered in some detail. A Proof-of-Principle experiment is suggested.     

Relativistic effects in the traveling-wave amplifier

A relativistically correct large-signal theory is developed for the analysis of high-power, axially symmetric traveling-wave amplifiers in order to investigate the physical phenomena involved in the interaction process. The nonlinear integro-differential system equations are developed from the Lorentz force equation, the one-dimensional equivalent circuit equation, the wave equation, and the continuity of charge relation. These equations are applied to two electron stream models: a ring model which permits the effects of nonlaminar flow and space-charge forces to be evaluated, and a disk-electron model in which these effects are ignored. The ring model space-charge fields are obtained from the appropriate Green's function for Poisson's equation in a moving frame of reference. Numerical solutions are presented and discussed with major emphasis on the disk-model solutions. The principal results are that the gain per unit length decreases with increasing beam velocity, the circuit phase velocity for optimum power output approaches the dc beam velocity u0, asu_{0}/capproaches unity, and the conversion efficiency is almost independent of u0for the synchronous case. The linearized one-dimensional theory of the traveling-wave tube is also discussed. Several of the large-signal results are predicted from the small-signal theory.     

An experimental wide-band gyrotron traveling-wave amplifier

Initial tests of a fast-millimeter-wave wide-band gyrotron traveling-wave amplifier (gyro-TWA)of novel design have demonstrated a small-signal 3-dB bandwidth of 13 percent with 18-dB gain at midband (35 GHz)using a 70-kV 1-A annular electron beam. This reflection-type amplifier using the TE01circular-electric mode has a linear tapered Waveguide circuit with an axial magnetic field profiled to maintain synchronism.     

A large-signal analysis of the traveling-wave amplifier: Theory and general results

Equations are derived describing the large-signal operation of the traveling-wave amplifier, including the effects of ac space charge and attenuation along the helical slow-wave structure. The equations constitute a system of nonlinear partial-differential-integral equations valid with reasonable approximations for all values of the parameters which are encountered in typical high-power traveling-wave amplifiers. The parameters which appear in the equations are the relative injection velocity b, the gain parameter C, the large-signal space-charge parameters K and B, the loss parameter d, and the input-signal level A0. The working equations were programmed for and solved on the Michigan Digital Automatic Computer, MIDAC, located at the University of Michigan's Willow Run Research Center. The rf voltage amplitude A(y), the phase lag of the rf wave relative to the electron stream θ(y), and the velocity deviation 2Cu(y, φ0) were computed and plotted for several values of C, K, b, and B at A0= 0.0025, and d = 0. Also, distance-phase plots are presented for each of the above cases. These flight-line diagrams for the traveling-wave amplifier are similar to the well-known "Applegate diagram" associated with klystrons. Zero-space-charge solutions are presented for C = 0.05, 0.1, and 0.2 with b as the parameter in order to determine the value of b which gives the maximum saturation gain and the optimum tube length. For C = 0.1 similar solutions are obtained for several values of the space-charge parameter K. Presented in graphical form, the results of these various solutions shed a considerable amount of light on the high-level operation of the traveling-wave amplifier.     

Development of a medium power L-band traveling-wave amplifier

The development and performance of a high gain medium power traveling-wave amplifier are described. Powers up to 7 watts at 15 per cent efficiency have been achieved. The small signal gain approaches 50 db in the middle of the band, and exceeds 35 db over a 2 to 1 range of frequencies. The tube itself consists of a glass-supported helix with a metal shell at one end housing the cathode structure, and a copper collector at the other end. The input and output couplings are made by means of coupled helices which are mounted in a brass tube or matching structure which is external to the vacuum envelope. The matching structure is supported in the focusing solenoid.     

Theory of a wide-band distributed gyrotron traveling-wave amplifier

We present the concept of an ultra-wide-band distributed gyrotron traveling-wave amplifier for millimeter and submillimeter waves. The radius of the waveguide in the interaction region is increased along the axis, while the strength of the dc magnetic field is decreased in such a way that the wave cutoff frequency is kept nearly equal to the electron cyclotron frequency. The basic principle of operation, peak gain, and saturated efficiency are analyzed. It is shown that instantaneous bandwidth over at least two octaves is theoretical possible. Technological requirements for achieving such an amplifier are assessed, including proposed structures for distributed input wave coupling.     

All-optical frequency conversion in a traveling-wave semiconductorlaser amplifier

All-optical frequency conversion over the entire gain spectrum of a traveling-wave semiconductor laser amplifier is analyzed by numerical solution of a nonlinear wave equation system. The wavelength dependence of the gain coefficient g, the linewidth enhancement factor α, the differential gain dg/dN, and the gain saturation effect are contained in the model. The method yields a high conversion efficiency and a converted signal output power up to 10 dBm is obtainable. It is shown that the input signal power can vary by three orders of magnitude with nearly no degradation of the conversion efficiency. By means of the input powers, the conversion efficiency can be maximized. The dependence of the conversion efficiency is analyzed for fixed input powers. Simultaneous conversion of an optical data signal to several wavelengths is analyzed. The requirements for the output filter are outlined     

返波激励的级联折叠波导行波放大器

利用折叠波导返波振荡器(FW-BWO)作为激励源,用于激励工作频率为216 GHz的折叠波导行波放大器.利用3D-Magic进行仿真实验,通过仿真优化,最终得到96 W的输出功率,整个电路的长度被设计为只有1 cm左右.通过该方法,显著地缩短了高频结构长度,有利于实现小型化的真空电子学太赫兹源,对集成化的太赫兹源设计具有重要的参考价值.     

A monolithic GaAs 1 - 13-GHz traveling-wave amplifier

This paper describes a monolithic GaAs traveling-wave amplifier with 9-dB gain and ± 1-dB gain flatness in the 1-13-GHz frequency range. The circuit is realized in monolithic form on a 0.1-mm GaAs substrate with 50-Ω input and output lines. In this approach, GaAs FET's periodically load input and output microstrip lines and provide the coupling between them with proper phase through their transconductance. Experimental results and the circuit details of such a structure are discussed. Initial results of a noise analysis and predictions on the noise performance are also given.     

Ring-plane traveling-wave amplifier: 40 KW at 9 MM

A 9-mm traveling-wave tube (TWT) amplifier using a ring-plane circuit is described. This tube has produced a peak power of 43 kw at an efficiency of 12 per cent(2C)with a solid beam. Several guns producing solid and hollow beams have been used with comparable results at high voltages (15 to 100 kv) and low currents (0.11 to 3.8 a). A waveguide transition (special coupler) incorporating a magic tee is used to couple independently to the two modes that can exist on the slow-wave circuit. The circuits, due to their good heat dissipation capability, can be operated either pulsed or CW. Their large size (ka= 1, 2, 3 ...) with useful cross sections comparable with those of ordinary waveguides, makes them attractive for producing kilowatt powers even at much higher frequencies.     

1.5 µm GaInAsP traveling-wave semiconductor laser amplifier

This paper presents a theoretical and experimental study in terms of small-signal gain, signal gain saturation, and noise characteristics of a 1.5 μm GaInAsP traveling-wave amplifier (TWA), realized through the application of SiOxfilm antireflection coatings. This TWA, having a residual facet reflectivity of 0.04 percent, exhibits a wide, flat signal gain spectrum and a saturation output power of +7 dBm at a 20 dB signal gain. The TWA also has a noise figure of 5.2 dB, which is the smallest value reported for semiconductor laser amplifiers. The experimental results are confirmed to be in good agreement with the theoretical predictions based on the multimode traveling-wave rate equations in conjunction with the photon statistic master equation analysis, which takes into account the amplifier material and device structural parameters. Signal gain undulation, saturation output power, and noise figure are also theoretically evaluated as functions of the facet reflectivity. The superior performance of the TWA demonstrates that the device is favorable for use in linear optical repeaters in fiber transmission systems.     

Computer simulation of the helix traveling-wave amplifier with harmonic signals

Both fundamental and second-harmonic output powers have been computed with an axially symmetric three-dimensional model of a helix traveling-wave amplifier. They agree reasonably well with measurements. For three beam power levels, the computed transfer curves show RF drive powers consistently about 3 dB below the measured powers and saturated output powers about 2 dB below the measured values. Inaccuracies in the assumed initial beam radius, density and velocity may have caused these differences. Suppressing the second harmonic raises the computed fundamental output power by 3 dB. The model accurately reproduces a measured 11 dB dip in the second harmonic as the fundamental signal saturates.     

A broad-band slow-wave structure for a millimeter traveling-wave tube amplifier

A new filter-type slow-wave structure, which is considered as an interdigital line loaded with inductance in shunt, is described in this paper. The results of the cold-test study of the structure are presented in terms of the phase velocity and impedance measurements. For the structure studied, interaction takes place between multiple electron streams and the axial electric field of the +1 space harmonic. The circuit has broad-band properties of phase and interaction impedance as a circuit for a traveling-wave amplifier. The maximum deviation of the phase velocity for a 30 per cent bandwidth has a value on the order of ±0.3 per cent. The structure is suitable for use as a high-power amplifier operating with a 20 per cent bandwidth in the millimeter-wave region.     

Waveguide-vane coupled slow-wave structure suitable for a high-power traveling-wave amplifier

A class of slow-wave structures, previously proposed for use in the magnetron amplifier, is examined in the linear version for application in a high-power, traveling-wave amplifier. Two versions are studied, both theoretically and experimentally, with particular emphasis on the frequency range suitable for wide-band, high-voltage application.     

The GaAs traveling-wave amplifier as a new kind of microwave transistor

A versatile solid-state microwave amplifier has evolved from a combination of transistor mechanisms and the transferred-electron effect. The prototype device, called a "traveling-wave transistor," employs a 2-µm layer of n-type GaAs grown epitaxially on a semi-insulating substrate. A transistor-like input launches a traveling space-charge wave that grows exponentially as it moves along the surface to a relatively distant output. There it is converted back into an electromagnetic wave. The long distance between input and output minimizes the feedback capacitance that often limits gain and bandwidth in high-frequency devices. Twelve experimental units show broad-band net gain in X band, with 10-30-dB built-in isolation. One unit exhibits instantaneous net gain from 6.7 to 15.3 GHz; another yields 28 dB at 9.2 GHz. All devices are good for linear microwave signal processing: voltage-controlled phase modulation at constant net gain, or voltage-controlled gain modulation at constant phase. Different bias conditions make possible threshold-sensitive saturated-amplitude amplification of pulses or sinusoids for logic or digital functions.     

Wideband traveling-wave tube for a X/Ku-band vacuum solid-state amplifier

Results of the numerical simulation of the slow-wave structure and the electron-optical system of a wideband continuous-wave traveling-wave tube with an output power of 250 W and gain of 23 dB, which is designed for operation in an X/Ku-band vacuum solid-state amplifying module, are given.     

A UHF traveling-wave amplifier tube employing an electrostatically focused hollow beam

The increasing importance of beam-type microwave devices has stimulated interest in focusing methods other than the usual uniform magnetic field. One such method applicable to hollow cylindrical beams, proposed by L. A. Harris, utilizes a radial electric field acting on a spinning beam to counterbalance the space-charge divergence forces. A traveling-wave amplifier operating in the 300 to 600 mc region, employing this focusing method, was designed and constructed. Experimental results obtained with this tube are presented. Beam transmissions as high as 90 per cent and net gain over 15 db were obtained. Practical considerations and tube design factors are discussed. The primary advantage of this kind of focusing is in the elimination of the solenoid, and consequent reduction in power supply requirements and weight, accessibility of rf connections to the tube, and elimination of capsule and aligning adjustments. This focusing method appears to have great potential usefulness in hollow-beam applications, and particularly in devices where the spiral motion of the beam can be made to interact with a spirally traveling wave.     

Characteristics measurement of gain and refractive index of traveling-wave semiconductor optical amplifier

A novel method to measure the gain and refractive index characteristics of traveling-wave semiconductor optical amplifier（TMA） is presented. In-out fiber ends of TWA are used to construct an external cavity resonator to produce big ripple on amplified spontaneous emission（ASE） spectrum. By this means,Hakki-Paoli method is adepted to obtain the gain spectra of TWA over a wide spectral range. From measured longitudinal mode spacing and peak wavelength shift due to increased bias current, we further calculate the effective refractive index and the refractive index change. Special feature of refractive index change above lasing threshold is revealed and explained.     

A nonlinear image contrast amplifier

Thermal picosecond light scattering involving the amplification of weak beams interfering with a strong beam in absorbing liquid media provides a mechanism for amplifying the contrast of weak optical images.