四次谐波级联二阶非线性效应传输特性数值分析

得到四次谐波多级级联二阶非线性耦合方程的近似解析解.数值分析了各参数对基波非线性相移、二次谐波和四次谐波功率的影响.     

行波管高频参量对二次谐波的影响分析

慢波系统的高频参量决定了行波管的功率和增益特性,谐波与基波频率下的高频参量的关系决定了行波管输出的谐波与基波的比例。本文在较宽的参数变化范围内对比分析相速、耦合阻抗在频带内的不同分布状态对低端的二次谐波比的影响。计算结果表明,相速之比为0.96 附近对应为二次谐波比最大的状态,此变化规律与频率的相关度较小;而谐波与基波的耦合阻抗之比越大,二次谐波比越大。对于宽带行波管,在翼片加载的高频结构中调整翼片内径就可以使输出的二次谐波比产生较大变化。     

二次晶体中准相位匹配孤子的激发与传输

采用分步积分法,研究了形状为双曲正割平方的光束在线性和非线性极化率均被调制的一维准相位匹配(QPM)二次晶体中的传输特性.数值计算表明,在仪有基波(FW)注入的情况下,基波迅速激发出基态孤子,并呈现出固有的振荡态,二次谐波(SHW)虽然激发出谐波孤子,但相应的色散波现象比较明显;在同时注入基波与二次谐波的情况下,当它们的振幅和光束宽度满足一定条件时,两者均能够激发出稳定的孤子态,并且基态孤子的振荡更具周期性,二次谐波的色散波现象显著减弱.同时,注入的二次谐波的振幅存在一个临界值,可使激发的二次谐波孤子达到最佳孤子态.     

凹球面自聚焦声场非线性效应的研究

用球束方程(SBE)研究了声源参数和媒质特性对凹球面自聚焦声场非线性效应的影响。结果表明,谐波的最大幅值出现在声焦点附近,基波与线性声场的分布类似,而高阶谐波的聚焦性能更好。超声频率、声源表面初始声压幅值或非线性参数越大,即平面波冲击间断形成距离越短,声的非线性效应越明显。声衰减会使非线性效应减弱,而凹球面曲率半径增大会使谐波和基波最大值的位置偏离更明显。     

基于经验模态分解的管道超声回波信号识别

在管道超声无损检测中,超声回波信号常受到噪声干扰或者因管道壁缺陷原因导致回波波形重叠,故检测信号很难判断缺陷大小。现采用一种基于经验模态分解(Empirical Model Decomposition,EMD)的方法,对超声回波信号的到达时间进行准确识别。该方法首先把原始采集的超声回波信号进行经验模态分解,预处理回波信号中的噪声干扰,处理后的信号通过正交检波处理得到该信号的峰值包络,则该包络的峰值时刻对应了回波信号的到达时刻。通过对实测缺陷信号的试验,验证了该方法的可行性和准确性。     

三腔回旋速调管预群聚电流谐波分量研究

该文基于小信号理论导出多腔回旋速调管预群聚电流密度谐波分量与群聚参数之间的关系,并以三腔回旋速调管为例进行了相应的数值计算。结果表明:二次谐波分量明显地小于基波分量,并且二次谐波分量随第二腔群聚参数变化起伏相对于一次谐波分量变化较大;二次谐波分量与第二腔群聚参数依赖关系与群聚腔的场强幅度的相位,第一漂移区引起电子相位变化有关;输入腔Q值在一定范围对谐波分量影响极小。     

FET基波和谐波振荡器的大信号设计

本文根据测出的FET的小信号S参数和静态,I-V特性建立了场效应管的大信号模型,然后应用谐波平衡法对FET基波和谐波振荡器进行了分析和优化设计,得到了振荡器稳态时的电流值。并采用一种简化的CAD方法求出了最佳功率输出时的外电路参数。在此基础上,研制了基波和Q波段、二次谐波振荡器。实验结果与理论分析基本一致。     

非线性目标谐波散射特性建模研究

非线性目标的入射功率-散射谐波功率曲线（后文简称为谐波散射特性）对增强非线性探测系统的鲁棒性和后续的目标分类识别具有重大意义.本文研究了非线性目标谐波散射特性的建模方法和对应的参数求解方法.文章通过建立等效电路,导出了非线性伏安特性曲线与散射参数的关系模型,并提出一种基于优化的递进求精解法来提高模型参数的求解效率;以齐纳二极管的实测基波数据作为建模求解的测试示例,结果表明建模参数的仿真谐波曲线与测量的谐波曲线在测量功率段均符合较好.故本文建模方法可为后续更多非线性目标（如PIN管、三极管等）谐波散射特性的获取提供有益指导.     

腔内二次谐波发生器

日本东京芝浦电气公司发表了一种腔内二次谐波发生器。在光谐振腔内置放一个二次谐波发生器件,对由激光振荡器发射出的射束的倍频有影响。在这种情况下,要求作为二次谐波发生器件用的非线性光学晶体应符合以下条件: 1.此晶体要能够从基波到谐波之间进行极为有效的变换。 2.此晶体的光损耗一定要小,尤其要具有良好的光均匀性,即基波和谐波之间的相     

晶体球中非相位匹配二次谐波产生测量铌酸锂非线性系数

本文利用晶体球中非相位匹配二次谐波产生测量晶体二阶非线性系数的理论分析和实验结果。用 35皮秒脉冲光源泵浦的非相位匹配二次谐波转换效率可达 12 % ,测得的LiNbO3 晶体非线性系数d3 1=- 6 .48± 0 6 pmV-1,d2 2 =2 .2 6± 0 .3pmV-1。     

Performance comparison of three different estimators for theNakagami m parameter using Monte Carlo simulation

Nakagami distribution has proven useful for modeling the multipath faded envelope in wireless channels. The shape parameter of the Nakagami distribution, known as the m parameter, can be estimated in different ways. In this contribution, the performance of the inverse normalized variance, Tolparev-Polyakov, and the Lorenz estimators have been compared through Monte Carlo simulation, and it has been observed that the inverse normalized variance estimator is superior to the others over a broad range of m values     

Mode Competition and Self-Consistent Simulation of a Second Harmonic Gyrotron Oscillator

A nonlinear numerical simulation of a second harmonic gyrotron oscillator is presented in this paper. Mode competition from a competing fundamental mode is investigated. In addition, a self-consistent nonlinear theoretical model, including the effect of velocity spread, is applied to analyze the second harmonic gyrotron. A series of numerical calculations is carried out for different electron beam parameters. The results are compared with that of calculations using the cold-cavity, fixed field approximation and with experiments. Good agreement is found between our calculations and an experiment at Fukui University. The azimuthal polarization of the field and the choice of the electron beam radius are also discussed.     

宽带功率放大器的非线性研究

功率放大器更多时候是工作在饱和区,此时其非线性特性成为需要考虑的重要因素之一。在宽带功率放大器中,低频段信号的二次谐波也在其工作频带之内。当前级功放模块产生的二次谐波与基频信号同时进入末级功放时,产生的二阶交调信号频率与基频相同,对输出造成影响。文中从理论上分析了放大器的非线性表现形式以及产生的机理,介绍了 X参数的优势,利用NVNA网络分析仪提取X参数,并且使用ADS软件进行谐波平衡仿真,研究了宽带功率放大器中二次谐波的相位对基频功率的影响。     

Statistical modeling of the indoor radio channel at 10 GHz throughpropagation measurements .I. Narrow-band measurements and modeling

The aim of this paper is to report the results of a propagation measurement experiment to reach a statistical model of the indoor radio channel at 10 GHz using directive antennas at both terminals. The measurements were conducted on a floor of a university building. The distribution of the received fading envelope was tested to fit the Rayleigh and Rician distributions, but were not satisfactory. The Nakagami distribution was found to give an excellent fit with its parameter, m, depending on the separation between transmitter and receiver. The results of the level crossing rate (LCR) and the average duration of fades (ADFs) confirmed this result. The effect of using reception diversity to improve the quality of the received fading signal was tested. Frequency, space and polarization diversity were applied and the cross correlation between the envelopes of the received fading signals (magnitude and power) in the diversity branches was evaluated. The diversity gain achieved was also evaluated. The effect of three different combining techniques (selection, equal gain and maximal ratio) and the effect of applying a global or moving means to the recorded data was studied     

Approximation of envelope statistics with Nakagami distribution foroutput of noncoherent diversity combiners

A simple relationship for estimating the fading parameter m of the Nakagami distribution is obtained for the output of L-branch noncoherent diversity combiners when the branch signals of unequal mean powers are independently Rayleigh faded. Comparisons between the exact distributions and the Nakagami distribution with approximated ms for L=2 and L=3 show good agreement over wide ranges of relative mean powers between the branch signals     

Time-domain envelope measurements for characterization and behavioral modeling of nonlinear devices with memory

This paper presents a calibrated four-channel measurement system for the characterization of nonlinear RF devices such as power amplifiers. The main goal of this study is to perform the characterization of the bandpass response of a nonlinear device-under-test (DUT) driven by modulated carriers. The proposed setup enables the generation of L- or S-band (1-4 GHz) carriers with a modulation bandwidth up to 100 MHz. The carrier harmonics generated by the nonlinear DUT are ignored and considered to be sufficiently filtered. This characterization setup enables calibrated time-domain measurements of the complex envelopes of both incoming and outgoing RF waves at the input and output of the DUT. This means that the fundamental and harmonic frequencies of the envelope are measured and processed. A large set of modulation formats can be generated by using a computer-controlled arbitrary waveform generator. Complex envelopes are measured by using a four-channel sampling scope. The proposed calibrated setup can be used to study or to validate linearization techniques of power amplifiers. This characterization tool is also well suited for the extraction and validation of behavioral bilateral models of nonlinear RF analog equipment exhibiting memory effects.     

Proposal for generation of intensive single-frequency beam by second harmonic generation of an FM laser beam

An arrangement that allows the generation of a single-frequency beam at the second harmonic is proposed. Essentially, frequency addition is performed of two signals that are frequency modulated with equal and opposite frequency excursion. For maximum efficiency, the modulator and the nonlinear crystal are arranged inside optical resonators for fundamental and harmonic frequencies.     

Outage probabilities of cellular mobile radio systems with multipleNakagami interferers

Closed-form expressions for outage probabilities of mobile radio channels experiencing multiple, cochannel, independent Nakagami interferers are derived. This is done for the case of Nakagami fading alone with an arbitrary number of interferers. Analytical results for the case of Nakagami fading combined with log-normal shadowing are obtained for a single interferer. The case of multiple shadowed interferers is examined by simulation. The fading severity parameter in the Nakagami distribution may be varied to model different fading conditions. Interferers with similar and different Nakagami statistics are analyzed. The probability of cochannel interference is related to the reuse distance, which is one of the key parameters in the design of cellular mobile radio systems. In addition, the effects of specifying a minimum signal power requirement for satisfactory reception are investigated. A number of system examples that illustrate applications of the results are included     

射频SAW器件非线性信号的测量及产生机制分析

射频前端的高度集成和高能量密度使声表面波(SAW)器件的非线性问题愈发严重。该文搭建了射频SAW器件非线性信号的测量系统,对SAW谐振器的二次谐波(H2)和三次谐波(H3)信号进行了准确测量。分析测量结果,讨论了非线性谐波信号的产生机制,并通过非线性有限元(FEM)模型仿真结果与测量结果拟合对比,验证了介电非线性和声应变的非线性效应对谐波产生的影响,为进一步研究非线性抑制方法,设计高线性度SAW器件提供了重要支撑。     

Evaluation of Nakagami fading behaviour based on measurements in urban scenarios

It is well known that the short-term fading conditions of the received envelope in wireless communications channels can be modelled by means of the Nakagami distribution. The value of the m parameter, also called shape factor, indicates the severity of multipath fading, and is a measure of channel quality, making its estimation necessary in many applications. In this letter, a range of possible values of the m parameter based on the analysis of a measurements campaign in urban scenarios is presented.