Spatial and frequency selection of waves in pseudoperiodic slow-wave structures

The principles of the joint selection of spatial harmonics and the extension of passbands of pseudoperiodic slow-wave structures (SWSs) are considered. Relationships for calculating the continuous spectrum of spatial harmonics are presented. Recurrence formulas for determining the input reflection coefficient from an SWS section are derived and used for the analysis of frequency characteristics. Selection of spatial harmonics and transformation of passbands in pseudoperiodic folded SWSs (a folded waveguide, an interdigital structure, etc.) are investigated. The possibility of extraction of either the first or the fundamental spatial harmonic in a frequency band from 30% to one octave and simultaneous suppression of spurious harmonics, including backward waves, is demonstrated. Owing to this feature, pseudoperiodic SWSs can be used in high-power wideband traveling-wave tubes.     

Nonresonant perturbation measurements on dispersion and interactionimpedance characteristics of helical slow-wave structures

A nonresonant perturbation (NRP) theory is developed from first principles for the measurement of dispersion and interaction impedance characteristics of a helical slow-wave structure (SWS). The phase of the reflected signal from a test helical structure varies when a perturber, also in the form of a helix, is moved along the axis of the test structure. The variation of phase with perturber position is interpreted to find the phase velocity of the structure under test. The interaction impedance of the structure is found by measuring the change in the axial phase-propagation constant of the structure as a dielectric rod is placed along the axis of the structure. Measurements are carried out with the help of an automated setup using an HP 8510 vector network analyzer (VNA) and a PC to collect the phase informations for the various precisely controlled positions of the perturber using a stepper motor, which is also interfaced with the PC. The experimental and theoretical values of the phase velocity and the interaction impedance of a typical “cold” experimental helical structure for a wide-band TWT are found to be close within 0.5% and 5%, respectively, in an octave band of 8-16 GHz     

Analysis of the dispersion characteristics of slow-wave structures with two microwave propagation channels

Models of rectangular and axially symmetric resonator slow-wave structures, which are built using transmission matrix for determining the characteristics of the slow-wave structures in different operation modes, are investigated. Elements of the transmission matrix are determined from the results of 3D simulation with the use of the HFSS software. In the analysis of the dispersion characteristics, slow-wave structures with two microwave propagation channels are studied and simulated using a 4×4 transmission matrix.     

Measurement of dispersion and interaction impedance characteristics of slow-wave structures by resonance methods

The measurement of dispersion and interaction impedance of slow-wave structures from cold tests using resonance methods is described. The theory behind the measurements is given, stressing the assumptions made. Some of the shortcomings of the simple perturbation theory of interaction impedance measurement are explained. This simple theory is then developed to take account of two complicating factors which are often tacitly ignored: transverse fields and space harmonics other than the fundamental. It is made apparent that where these complications exist a reliable estimate of the interaction impedance can be made only if an approximate theory of the structure is available. Experimental details are given, including common difficulties and, where possible, methods of surmounting them.     

Output characteristics of high-power low-voltage broadband traveling-wave tubes with helical and ring-rod slow-wave structures

The output characteristics of high-power low-voltage broadband traveling-wave tubes (TWTs) of the C-D band are presented. The decisive role of a continuous high-perveance electron beam provided by a sectoral electron gun is demonstrated. The main features of the TWT computation procedure are described and the results of comparison between calculated and experimental data are presented.     

Dielectric slow-wave structures for the generation of power at millimeter and submillimeter wavelengths

Several new types of coupling structures, designed to extract energy from a megavolt electron beam at a harmonic of the frequency used to modulate the beam current, are considered. In particular, the advantages of a slow-wave device over a right cylindrical cavity are indicated. The slow-wave coupling device may be resonant or nonresonant; the latter corresponds to a Cerenkov radiator. Power measurements at the twelfth harmonic of the fundamental modulating frequency provide good correlation with the theoretical power output expected. The design of a submillimeter coupling device is described, and the theoretical pulsed power obtainable is shown to be at the milliwatt level for a harmonic current density of 74 ma/cm².     

One-third-of-pitch reduction technique for the analysis of ternary azimuthally periodic helical slow-wave structures

This paper presents a technique to reduce the standard single-pitch helical model when performing a full-wave analysis of helical slow-wave structures (SWSs). The technique makes use of azimuthally periodic boundary conditions applied to the conventional helical SWS; the ternary angular symmetry of its dielectric rods allows reducing the standard computational domain by two thirds. It has been demonstrated that this method, as implemented with a commercially available simulator (high-frequency structure simulator), has no impact on the stability and accuracy of the cold parameters but allows a significant reduction of simulation time, which increases with the accuracy of the results. The proposed technique is therefore perfectly suitable for the accurate modeling of complex geometries and is expected to be particularly attractive for optimization analyses and applications in which accuracy and short simulation time are main concerns.     

Analysis of the dispersion characteristics in the vicinity of the passband boundaries of the slow-wave structures that represent chained cavities

A model of the slow-wave cavity structures that can be used for the analysis of electrodynamic parameters and excitation by the fixed current is electrodynamically substantiated. A possibility of the calculation of electrodynamic parameters using the 3D simulation is demonstrated for the slow-wave cavity structures. The calculated electrodynamic parameters of the two- and four-port slow-wave structures are presented.     

两种新型微波管慢波结构的高频特性仿真研究

慢波结构是微波管重要的部件,它是电子注与高频场相互作用进行能量交换以实现微波振荡或放大的场所。随着对微波管性能越来越高的要求,微波管慢波结构的效率和性能要求也随之提高。文中首先分析了如何求解微波管慢波结构的高频特性,并在此基础上使用了HFSS以及CST MWS等软件对两种新型微波管慢波结构(环杆慢波结构、折叠波导慢波结构)的高频特性(色散特性、耦合阻抗)进行了初步的仿真研究,并通过对结果的分析比较了两个结构的特性。     

Fault mode single-phase operation of a variable frequency inductionmotor drive and improvement of pulsating torque characteristics

Improved reliability and fault tolerant operation of power converter systems are extremely important for industrial AC drives. The paper considers variable frequency variable voltage operation of a three-phase induction motor in single-phase mode for two common faults of a three-phase inverter, i.e., open base drive and device short-circuit. The motor performance has been extensively analyzed in single-phase mode and remedial strategies have been developed to neutralize large second and other lower order harmonic pulsating torques. In a single-phase open loop volts/Hz control made of a faulty three-phase inverter, it has been demonstrated that odd harmonic voltages at appropriate phase angles can be injected to neutralize the low frequency pulsating torques so as to permit smooth drive operation. It has been shown that the pulsating torque can be further reduced by load dependent flux programming rather than operating with constant rated flux     

差频Ronchi光栅的频谱特性与在图象处理中的应用

用两个不同空间频率的Ronchi光栅相迭置,可得到差频Ronchi光栅,文中讨论了这种光栅的频谱特性,并以此作为滤波器对图象进行一阶、二阶微分处理以及对由于匀速运动而造成的模糊图象进行还原处理.     

Measurements of unity gain cutoff frequency and saturation velocity of a GaN HEMT transistor

The measured intrinsic saturation velocity (v/sub si/) of carriers in a gallium nitride (GaN) high electron mobility transistor (HEMT) is very much lower than that predicted using Monte Carlo simulation. A novel method of extraction of the intrinsic saturation velocity (v/sub si/) of carriers has been developed utilising the deembedded s-parameters, thus enabling the calculation of v/sub si/ over a wide range of bias conditions. The method is equally applicable for gallium arsenide (GaAs) and indium phosphide (InP) based transistors. The measurements indicate for GaN-based HEMT a maximum deembedded saturation velocity of 1.1/spl times/10/sup 5/ m/s close to the pinchoff voltage (V/sub P/). It was found that self-heating had only a weak effect on the saturation velocity up to junction temperatures approaching 140/spl deg/C above ambient.     

中心凹陷W型光纤截止特性的研究

对中心凹陷W型光纤严格按照矢量法,利用光场的电磁边界连续条件建立解析模型得到特征方程,通过数值计算分析了凹陷深度和宽度对中心凹陷W型光纤的基膜HE11和高次模TE01截止波长、单模工作区间和基膜能量损耗的影响,并与相同结构参数的W型光纤进行了比较。     

Upper cutoff frequency of the bound wave and new leaky wave on theslotline

Printed-circuit lines exhibit interesting behavior due to leakage of power. We have attempted to work toward a more profound understanding of uniplanar circuit properties when it comprehends planar transmission lines. Our work has focused on the slotline. We realized that the solution of its dispersion equation is multivalued. This enabled us to identify and report a new leaky wave on the slotline. The leaky wave brings down the upper cutoff frequency of the bound wave propagating over the slotline due to overlapping of the bound- and leaky-mode regions. For this case, we present some simple closed-form formulas providing this frequency limit when there is a frequency gap or when simultaneous propagation of the bound and the first or second leaky wave occurs. Propagation of the bound and leaky wave at the same time is a straightforward consequence of the multivalued nature of the solution of the dispersion equation. Evolution of the real and complex improper solutions of the equation in dependence on slotline dimensions demonstrates this clearly. We believe that conclusions drawn for the slotline also hold generally for other printed-circuit lines     

Calculation of the fundamental cutoff frequency in a case of waveguides of doubly connected cross section

The lowest cutoff frequency of a circular waveguide with a concentric inner polygonal domain is determined using a conformal mapping variational approach. The results are verified by means of a modified Randall's empirical rule. It is shown that this technique leads also to good relative accuracy in the case of polygonal domains with a concentric circular domain.     

短相干半导体激光器的射频调制特性及应用

短相干激光光源在进行高精度的干涉测量时,可以消除被测光学元件前后表面反射形成的杂散光,是低相干干涉仪的理想光源。针对低相干干涉应用对光源的需求,依据速率方程和激光调制特性对射频调制下的短相干半导体激光器光谱特性进行了理论研究。搭建了短相干光源系统,研究了半导体激光器斜率效率η、偏置电流I_b、射频信号频率f_m和幅度A_m对其相干长度的影响。实验结果表明,斜率效率大的半导体激光器更有助于短相干特性的实现,随着调制信号频率和幅值增加,工作在阈值附近的激光器相干长度随之降低,该系统在I_b=1.3Ith、f_m=950 MHz、 A_m=19 dBm的条件下获得了相干长度为90μm的短相干光源。并成功应用于斐索干涉仪上,获得了对比度K=0.931 8的清晰干涉图像,与现有短相干光源相比,对比度提高了约51.1%,实现了对平行平板玻璃面形的测量。     

Influence of wafer thickness and carrier recombination on the cutoff frequency of alloy-junction transistors

The influence of wafer thickness and carrier recombination on the -cutoff frequency of the “intrinsic” transistor is studied. First, M' solution of the diffusion of minority carriers in a symmetrical junction transistor is used to find the d.c. transport factor. This is then converted to the a.c. case and finally an implicit equation is found for the cutoff frequency as a function of wafer thickness θ and surface recombination velocity S. It is shown that, for S < 3000 cm/sec, the influence of surface recombination is negligible.

At very narrow basewidths the current density is very high at the emitter edge and this decreases the diffusion length. More important seems to be the fact that the carriers' path (from slanted edge of emitter to slanted edge of collector) is longer than the geometrical basewidth. A reduction in wafer thickness decreases this effect and thus increases the cutoff frequency, in spite of increasing the current density at the emitter edge. The most important equations have been represented graphically for the particular case of the STC TK20 transistor.     

Effect of annealing on the spectra of nuclear quadrupole resonance in gallium-indium selenides and characteristics of structures based on these materials

The results of studying the effect of low-temperature annealing (at temperatures no higher than 250°C) on the spectra of nuclear quadrupole resonance in layered GaSe and InSe single-crystal semiconductors are reported. The electrical and photoelectric characteristics of the p-GaSe-n-InSe structures have also been studied. It is shown that, as the annealing temperature is lowered to room temperature, the quality of the samples improves due to a decrease in the defect concentration in the crystals and due to ordering in a system of polytypes. The temperature conditions for the heat treatments, at which the main parameters of the heterojunction are improved, are determined. Mechanisms affecting the behavior of the p-GaSe-n-InSe structure during the course of annealing are discussed.     

Comparative analysis of the Curnow and Malykhin-Konnov-Komarov (MKK) circuits as representations of coupled-cavity slow-wave structures

Two lumped element models of coupled-cavity slow-wave structures, one due to Curnow (1965) and another due to Malykhin, Konnov, and Komarov (MKK) (2003), are compared. The basis of comparison is the level of accuracy with which the models reproduce the cold circuit phase velocity and characteristic impedance of the structures as functions of frequency, as obtained from numerical solutions of Maxwell's field equations. Two distinct types of coupled-cavity structure are analyzed using these two models. These are a C-band double staggered ladder circuit and an L-band slot coupled "Hughes-type" structure. We find for the C-band case, both the Curnow and MKK models give excellent representations of both the cavity and slot bands, but for the L-band case the Curnow model has no solution when an attempt is made to fit both the cavity and slot bands, while the MKK model accurately represents both bands in this case.