稳定的锁模Nd:YAG激光器

本专利叙述了通过反馈回路控制激光腔长使锁模Nd:YAG激光脉冲振幅及重复率达到稳定的方法与装置。激光器终端反射镜安装在以低频振动的压电晶体上,激光辐射的一部分1.06微米基波转换成二次谐波频率,二次谐波频率的平均功率被积分检波器接收,二次谐波功率的大小决定于激光腔光学长度与锁模频率之间的匹配。腔长由反馈回路进行控制,该回路对二次谐波探测器的输出和压电晶体的振动信号进行比较。     

一种具有深度二次谐波抑制的微波振荡器

微波振荡器作为通信系统中的关键器件,已经被广泛地研究和设计。因此,设计具有优秀性能的微波振荡器是至关重要的。提出一种具有深度二次谐波抑制性能的新型微波负阻型振荡器。该设计的新颖性在于利用一个装配于双极结型晶体管射极的并联结构(由一段短微带线和电容并联组成)来实现二次谐波抑制。该结构作为振荡器基波信号的反馈元件,同时作为二次谐波处的带阻结构。因为二次谐波没有反馈回路(接地),所以能被极大地抑制。更重要的是在振荡器的输出端无额外的滤波器来抑制二次谐波,这使得电路尺寸得以减小。给出了一个振荡器设计实例,并给出其测试结果来论证理论的正确性。测试结果表明相较于传统振荡器的二次谐波抑制度有25 dB 的提高。     

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。     

星上双频段多通道微波光子链路传输性能的优化研究

利用星上微波光子技术,将多个频段微波信号调 制到光域,可解决数据在星上的高 速处理和星间远距离传输等问题。当多频段微波信号进行 光学调制时,交调失真是影响星上多频段微波信号光域传输性能的重要因素。研究了星上双 频段、每个频段内2信道的微波信号光学调制方法,分别推导了Ku、Ka波段微波信号的输出 信号噪声失真比(SNDR)和无杂散动态范围(SFDR)表达式,分析了 各次谐波和各阶交调失真分量对链路性能 的影响,获得了保证链路输出SNDR最优的最佳直流偏置相位和调制系 数。利用OptiSystem软件建立了仿真模型,并进行了仿真验证。研究结果表明 ,Ku 频段中非线性交调分量包括自频段三阶交调(IMD3)分量、频段间IMD3分量 和频段间二阶交调(IMD2)分量;Ka频段中非线性交调分量包括自频段IMD3分量、Ku频段IMD2分量、Ku频段二次谐波(HD2)分量以及频段间IMD3分量。对于Ku频 段信号,当调制系数和直流偏置相位分别为0.17和0.535π时,SNDR取得最优值21.50dB;对于Ka频段信号,调制系数和直流偏置相 位分别为0.22和0.525π时,SND R取得最优值15.32dB。     

基于二次谐波注入的Doherty功率放大器

针对传统Doherty放大器在提高效率后会恶化线性指标的关键问题进行了分析与讨论。提出了一种基于二次谐波注入（SHI）的Doherty结构。采用GaN功率管CGH21240的仿真模型,设计了一款Doherty功率放大器。仿真结果显示,该放大器的效率在输出大于50dBm后可以达到47％以上,比平衡式放大器改善约15％;三阶交调在输出为53dBm时仍低于-30dBc;在输出为50dBm时,比未采用二次谐波注入改善约10dBc。该放大器结构简单,且实现了效率和线性的同时改善。     

基于InP HBT工艺的C波段高谐波抑制有源三倍频器MMIC北大核心

基于0.7μm InP HBT工艺,设计了一款C波段高谐波抑制有源三倍频器MMIC。三倍频核心电路采用AB类差分级联三极管(cascode)结构,可产生丰富的奇次谐波信号,通过输出匹配网络滤出三次谐波信号并抑制其他谐波信号。输入端利用有源巴伦实现单端信号到差分信号的转换,提供较大的驱动功率同时节省面积;输出端级联缓冲放大器,提高输出功率。常温状态下,当输入驱动功率为-5 dBm时,该三倍频器在输出频率3.9~6.9 GHz范围内,输出功率大于10 dBm,偶次谐波抑制度大于33 dBc,基波抑制度大于35 dBc,五次谐波抑制度大于24 dBc。芯片供电方式为单电源+3.3 V供电,直流功耗为198 mW。     

基于场效应管阻抗参数测试的宽带功率放大器优化设计

设计了一个工作在800～1250MHz的宽带线性高功率放大器.用负载牵引方法测试了LDMOS场效应管宽带内的大信号阻抗参数,利用测得的阻抗参数优化设计了功放的匹配电路.实测功放的1dB压缩点输出功率大于44.5dBm,二次谐波小于-25dBc,输出功率为38.5dBm时双音测试三阶交调(IM3)优于-44dBc.     

用外推法测量微波低噪声部件的三次交调特性

<正> 各种微波电路部件正日益广泛地应用于各种通讯设备中,三次交调特性的测量是对部件各种特性测量的重要环节。特别是对于各种低噪声前端,往往要测量它们小信号时的交调特性,由于仪表灵敏度的限制或由于背景噪声的影响,三次交调这个参数用常规方法往往测不准或根本无法测出。下面介绍一种用外推法测量微波低噪声部件三次交调特性的方法。 众所周知,理想的线性电路输入输出信号的频谱是不变的,也就是说信号通过这种部件并不会产生新的频率分量。但是由于实际电路总是或多或少的带有非线性,因此当有两个以上的载波频率输入到部件中后,其输出端除了输入频率分量之外,还会出现一系列的组合频     

应用于WiFi6的新型高线性度功率放大器设计

针对WiFi 6的设备需求,设计了一款工作在5.15 GHz～5.85 GHz的高线性度砷化镓异质结双极型晶体管射频功率放大器。为了保证大信号和高温下功率管静态工作点的稳定性,采用了一种新型有源自适应偏置电路。对射频功率检测电路进行了设计和改进,有效降低了射频系统的功耗。针对各次谐波分量产生的影响,对输出匹配网络进行了优化。仿真结果表明：该射频功率放大器芯片小信号增益达到了32.6 dB;在中心频率5.5 GHz时1 dB压缩点功率为30.4 dBm,功率附加效率超过27.9%;输出功率为26 dBm时,三阶交调失真低于-40 dBc。实测数据表明：小信号增益大于31.4 dB;5.5 GHz时1 dB压缩点功率为29.06 dBm;输出功率为26 dBm时,三阶交调失真低于-30 dBc。当输出功率为20 dBm时,二次三次谐波抑制到-30 dBc和-45 dBc。     

高效率小型化行波管的二次谐波抑制

以罗埃大信号理论为基础，利用两节螺距具有正负变化的双跳变输出电路对提高宽带行波管效率的二次谐波抑制问题进行了模拟。对输出电路的跳变位置和跳变螺距进行了详细研究。模拟与测试结果证明：采用双跳变输出线路，在低频端二次谐波受到很大抑制，正向基波分量得到明显增强，在宽频带(6—18GHz)范围内，获得了均衡的饱和功率输出。     

Hard-limiting of two signals in random noise

Two sinusoidal signals and Gaussian noise lying in a narrow band are passed through an ideal band-pass limiter that confines the output spectrum to the vicinity of the input frequencies. The output spectrum, consisting of both discrete and continuous components, is studied in terms of its corresponding autocorrelation function. The discrete output components are identified with the output signals and intermodulation products due to interference between the two input signals. The continuous part of the spectrum is associated with the output noise. The effects of limiting are expressed by ratios among the average powers of the output spectral components. Performance curves are given that show signal suppression, the ratio of output to input SNR's, and the relative strength of the intermodulation terms.     

The notch filter test method simulation for the intermodulationnoise of return path CATV amplifiers

CATV return path is mainly carrying QAM signals. The frequency spectrum of QAM digital signals is noise-like. This means, that a return path amplifier is loaded with wideband noise, and intermodulation products will be noise-like too. This article describes the numerical simulations of the notch filter test method for intermodulation noise distortion in return path CATV amplifiers. The calculation is based on the frequency dependent intermodulations coefficients of the second and third order as well as clipping effect. It is possible to calculate the return path distortion spectrum and the output level limit for any channel plan. The simulation proved to be in good accord with measurement     

Intermodulation Characteristics of X-Band IMPATT Amplifiers

The intermodulation products produced when two equal-amplitude signals are applied to the input of an X-band IMPATT-diode amplifier have been measured. An Si p+nn+ IMPATT diode was operated in a double-slug-tuned coaxial reflection amplifier circuit that was tuned to provide 20 dB of small-signal gain at 9.340 GHz. The intermodulation tests consist of measurements of the magnitudes and frequencies of the amplifier output signals as a function of the input-signal drive levels and frequency separations. The gain and single-frequency characteristics of the amplifer were also measured, and are used along with the theoretical device and circuit admittance characteristics as a basis for explanation of the intermodulation results. A low-frequency dominance mechanism is found to exist in which the low-frequency signals are amplifed more than the high-frequency signals. This mechanism becomes more significant as the amplifier drive level is increased.     

Signal and Interference Output of a Bandpass Nonlinearity

This paper deals with the passage ofmsignals along with additive Gaussian noise through a memoryless bandpass nonlinearity. It offers a method for finding the fundamental zone output attributable to anyninput signals (including their intermodulation) which at the same time specifies the equivalent new nonlinearity seen by these signals. The fundamental (i.e, bandpass) transfer characteristic of the original nonlinearity is arbitrary and may include AM-to-PM conversion. The approach is a generalization of Blachman's treatment of the problem for a signal-plus-noise jnpdt. The analysis is based on the author's previously reported stochastic decomposition method for multiple signals feeding a bandpass nonlinearity.     

Prediction of Gain Expansion and Intermodulation Performance of Nonlinear Amplifiers

A mathematical model for the input‐output characteristic of an amplifier exhibiting gain expansion and weak and strong nonlinearities is presented. The model, basically a Fourier‐series function, can yield closed‐form series expressions for the amplitudes of the output components resulting from multisinusoidal input signals to the amplifier. The special case of an equal‐amplitude two‐tone input signal is considered in detail. The results show that unless the input signal can drive the amplifier into its nonlinear region, no gain expansion or minimum intermodulation performance can be achieved. For sufficiently large input amplitudes that can drive the amplifier into its nonlinear region, gain expansion and minimum intermodulation performance can be achieved. The input amplitudes at which these phenomena are observed are strongly dependent on the amplifier characteristics.     

Large signal analysis of optical directional coupler modulators

Expressions are obtained for the output harmonic and intermodulation products of optical electrical coupler modulators driven by multisinusoidal input signals. The special case of relatively small input amplitudes is considered. The results are verified by comparisons with previously published results     

Analysis of semiconductor diodes with multifrequency input signal

In this paper a closed form expression for the intermodulation output power from a semiconductor diode driven by an arbitrary number of "small-level" input signals is obtained. The effect of the intrinsic resistance of the diode material is taken into consideration through the use of the modified exponential function for the diode characteristic. It has been found that the relative harmonic distortion depends on the bias voltage, which agrees with the experimental observations. This dependence would not have been obtained had the intrinsic resistance been neglected. Also, the calculated intermodulation output power shows good agreement, for small input signal, with the published experimental results.     

Optimization of Third-Order Intermodulation Product and Output Power from an X-Band MESFET Amplifier Using Volterra Series Analysis

A third-order analysis for accurately predicting large-signal power and intermodulation distortion performance for GaAs MESFET amplifiers is presented. The analysis is carried out for both single- and two-tone input signals using the Volterra series representation and is based only on small-signal measurements. Simple expressions for the nonlinear power gain frequency response, the output power, the gain compression factor, and the third-order intermodulation (IM/sub 3/) power are presented. The major sources of gain compression and intermodulation distortion are identified. Based on the developed nonlinear analysis in conjunction with the device nonlinear model, a systematic procedure for designing a MESFET amplifier under large-signal conditions for optimum output power and IM/sub 3/ performance is proposed. The method utilizes out of band computed matching compensation through a nonlinear model of the amplifier. The accuracy of the device large-signal and IM/sub 3/ distortion characterization and the practicability of the proposed method are illustrated through comparison between measured and predicted results.     

Prediction of Mixer Intermodulation Levels as Function of Local Oscillator Power

During intermodulation testing with diode mixers an increase of intermodulation interference was observed due to an increase of LO power incident to the mixer. This phenomenon conflicted with the theory that increase of LO power reduces intermodulation output of the diode mixer. In these tests the intermodulation decreased as expected when the LO power was further increased. Results of a theoretical and experimental study of how the level of incident LO power affects the intermodulation output levels emanating from the mixer are presented. The predicted results lead to the following experimentally verified conclusions. 1) A drop in power at some intermodulation frequencies occurs for an increase of LO power, depending on LO operating point and order of intermodulation. 2) Power at each intermodulation frequency will repeatedly increase, reach a maximum, and then decrease as power in LO signal increases, where the number of repetitions follows the orders of intermodulation. 3) The maximum intermodulation power at low-order intermodulation frequencies occurs for higher LO power than higher order intermodulation frequencies. LO power operating point is shown to be a significant factor in mixer intermodulation consideration. Application of these results to receiver intermodulation improvement is discussed.     

面向宽带接入与泛在感知应用的基于双波长的线性化光载无线链路

Radio-over-Fiber ( RoF ) technologies have been considered to be a promising solution to broadband access and ubiquitous sensing. We present a novel approach using dual-wavelength lights to suppress the nonlinear intermodulation distortion in intensity-modulated RoF link both theoretically and experimentally. The system we proposed mainly consists of two Laser Diodes (LDs ) at different wavelengths, a commercial available Mach-Zehnder Modulator (MZM) and a Photo Detector (PD). More than 25 dB suppression of the Third-order Intermodulation Distortion (IMD3) is achieved by adjusting the wavelength and optical power of the laser. Besides , the output of the MZM is then sent to the photodetector via a single fiber, which simplifies the system complexity for distribution of RF signals over long distances .