矩量法分析平面等角螺旋天线的脉冲辐射特性

对等角平面螺旋天线进行RWG边元建模,利用矩量法求天线表面电流,并进一步得到天线的输入阻抗、天线转移函数和脉冲辐射波形.研究显示:在工作频带内,天线的输入阻抗值约为自互补结构天线的输入阻抗理论值188.5Ω(满足巴比涅-布克原理[1]),即空间本征阻抗之一半,在超宽频带内,天线的转移函数具有平坦的幅频特性和较好的线性相频特性,用作脉冲辐射天线时,辐射电场波形具有高斯二次微分特性.     

平面火山烟雾形天线的脉冲辐射特性

设计了一种火山烟雾形平面印刷超宽带天线.研究显示其阻抗带宽低频端可达0.8GHz,在加载电阻回路后带宽低频端可扩展至0.5GHz,在1ns宽的高斯微分脉冲激励下,双锥天线作为发射天线,比较了加载电阻和未加载电阻天线的接收波形,由结果可知,加载天线可以进一步减小脉冲信号波形失真。     

平面阵列天线轴线能量的慢衰减特性

根据电磁理论,给出了平面阵列天线在皮秒高斯脉冲激励条件下,轴线能量传播特性的解析计算公式和数值模拟结果。用实验直接验证了瞬态电磁波的慢衰减特性。在实验误差范围内,理论计算与实验结果符合较好。对布阵方式的初步实验表明,适当的稀疏布阵可提高传输效率。     

圆环天线的时域有限差分分析

采用时域有限差分算法（FDTD）计算了圆环天线在高斯脉冲激励下的瞬时电流分布，通过付里叶变换，获得天线在不同频率下的稳态电流分布，经过进一步计算，得出天线在这组频率下的辐射方向图和输入阻抗。     

一种应用于卫星通信地面站的新型单臂螺旋天线及其阵列的研究

研究了一种应用于卫星通信地面站的新型单臂平面螺旋天线,该天线采用圆柱螺旋激励同轴线馈电,可以形成倾斜的波束,通过改变圆柱螺旋的参数可以调整其输入阻抗以达到阻抗匹配的目的.用矩量法求解了天线的电流分布和三维辐射方向图以及增益轴比等参数,计算结果与参考文献很吻合.为了增强天线的方向性系数和增益,以四元天线阵为例,研究了这种天线组成的天线阵的辐射特性,给出了天线阵的三维辐射方向图.计算结果表明,该天线组成的天线阵同样具有倾斜的波束指向,各天线单元的输入阻抗为接近50 Ω的纯电阻,增益比单个天线单元提高6.3 dB.     

具有金属平面反射器的振子天线

本文用混合法(MoM GO GTD)分析和计算了具有金属平面反射器的振子天线的输入阻抗和辐射波瓣图。实验表明,理论计算的波瓣图与实验结果是吻合的。当反射器尺寸很大时,输入阻抗数据与文献中的结果一致。随着反射器尺寸的减小,其电阻与电抗分量都有一定起伏是正确的,从而证实了用混合法分析这种型式天线是简单和有效的。     

曲线分段的矩量法分析阿基米德平面螺旋天线

从混合位积分方程出发,采用矩量法结合曲线分段的三角基函数和脉冲检验函数分析了阿基米德平面螺旋天线,给出了输入阻抗,电流分布以及辐射方向图结果.从曲线形式的海伦积分方程出发结合折线分段的脉冲基函数点匹配法比较结果与文献[2～4]十分吻合.由于采用了曲线分段,在相同分段数情况下其结果的精度将比采用折线分段的高.     

FDTD法计算高频单极天线特性

用时域有限差分法（Ｆｉｎｉｔｅ Ｄｉｆｆｅｒｅｎｃｅ Ｔｉｍｅ Ｄｏｍａｉｎ Ｍｅｔｈｏｄ）计算天线阻抗特性,可以使用不同的激励方式,文章比较了采用不同激励方式时,天线的输入阻抗。文中的主要内容是将表面阻抗法用于ＦＤＴＤ中,计算架设在介质平面上单极天线的辐射特性,并用ＦＤＴＤ法计算了介质平面上铺设不同尺寸的导体平面时,单极天线的输入阻抗随导体平面尺寸变化的特性。     

电光调Q脉冲激光外差研究

采用高斯函数模拟电光调Q射频激励波导CO2 激光器输出脉冲激光的波形 ,在理论上研究了脉冲激光外差的波形及其傅里叶变换频谱成分 ,并在实验上测量了脉冲激光外差的波形及其傅里叶变换频谱 ,理论分析与实验结果一致。     

球面螺旋天线的研究

研究了一种新型的球面螺旋天线,与传统螺旋天线相比,具有结构紧凑、尺寸小、增益高的特点,分析了两种不同模式下球面螺旋天线的辐射特性和输入阻抗;并首次提出了一种工作在圆锥模式下的半球面螺旋天线,具有更小的尺寸和良好的赋形波束,可应用于近地卫星通信。     

Plane wave pulse propagation through random media

The theory of plane wave pulse propagation through a random medium, under the forward-scattering assumption is presented. Since pulse propagation characteristics are determined by two-frequency mutual coherence functionGamma, a set of normalized curves is given forGammafor different propagation parameters (operating frequency, propagation distance, turbulence strength or density of scatterers, etc.). From the curves one can obtain the coherence bandwidth of a wave for a variety of situations. A received pulse form due to an input delta function is given in a normalized form which is applicable to the whole range of strong fluctuation. The results are applied to optical pulse propagation in dense clouds. It is shown that the high data rate optical pulse communication through clouds may be limited due to a narrow coherence bandwidth of the order of megahertz. A good agreement between the theoretical prediction and the available experimental data has been demonstrated for both the received pulse shapes and the pulse durations of an optical pulse in clouds.     

Amplification of ultrashort solitons in erbium-doped fiberamplifiers

Pulse amplification in erbium-doped fiber amplifiers is studied by considering a general model that includes both gain saturation and gain dispersion. The effects of gain dispersion are studied numerically for the case in which a fundamental soliton is launched at the amplifier input. The results show that fiber amplifiers may be useful for simultaneous amplification and compression of weak optical pulses. Under high-gain conditions the input pulse is found to split into a train of amplified subpulses whose width and repetition rate are governed by the gain bandwidth. The numerical results are in qualitative agreement with recent experiments     

Ultrashort optical pulse transmission characteristics of verticallycoupled microring resonator add/drop filter

The ultrashort optical pulse transmission characteristics of a vertically coupled microring resonator (VCMRR) filter were measured at 1.55 μm wavelength, and the transmission capacity per channel was evaluated. The pulsewidth at the output was measured to be 3.4 ps, when 1.2 ps input pulse with a sech pulse shape from a fiber laser was incident on the microring resonator filter with a fullwidth at half-maximum (FWHM) of 0.75 nm (94 GHz). From this result, the maximum transmission capacity of the filter was estimated to be approximately 50 Gb/s. The pulse broadening through the filter was theoretically analyzed, and it was confirmed that the pulse broadening evaluated from the bandwidth of the filter spectrum response were in good agreement with the measured results     

折返点匹配的宽带二倍频实验研究

在二次谐波转换中,基频光和倍频光的群速失配是限制转换带宽的主要因素。利用折返点匹配的宽带谐波转换技术能同时实现基频光和倍频光的相位匹配和群速匹配,理论计算表明在折返点匹配的情况下,倍频转换带宽将显著增加。分别利用厚度10 mm,氘含量12%的KD*P晶体和厚度12 mm的KDP晶体对中心波长为1053 nm,谱宽为31 nm,能量为620μJ的基频光进行折返点匹配二倍频和传统二倍频的对比实验,前者取得了22 nm的转换带宽,远大于后者7 nm的转换带宽。实验结果证实了理论计算的正确性,显示了折返点匹配宽带谐波转换技术的优越性。相应地,前者转换效率为25%,大于后者20%的转换效率,导致倍频转换效率较低的主要因素是入射基频光的光束质量和光谱质量较差。     

On Reducing the Period of Input Pulse Trains Using Coupled-Line Networks

The theoretical and experimental results on converting input pulse trains into bipolar pulse trains of higher speed are presented. The network used here for such functions consists of two strip-coupled lines and three resistors. The experiment shows good agreement with theory.     

高强度飞秒脉冲单块BBO晶体三倍频实验

针对脉冲宽度100 fs,带宽25 nm,能量6 mJ左右的超短脉冲基频光(经过透镜缩束后峰值光强为200~900 GW/cm2),采用单块厚度为1.5 mm的BBO晶体进行了三倍频实验研究。在入射基频光强度约300 GW/cm2时,得到的三倍频转换效率约0.8%。采用分步傅里叶变换及四阶龙格-库塔算法,对描述飞秒脉冲单块晶体三倍频的耦合波方程组进行了数值计算。研究结果表明,三倍频光主要是由三阶非线性效应产生的;基频光带宽较大是限制三倍频转换效率的主要因素之一;对基频光的入射角度及方位角进行优化,可较好地补偿非线性相位失配,提高单块晶体三倍频转换效率。     

光纤放大器中有限增益带宽对自相似脉冲放大演化的数值研究

通过求解包含超高斯增益系数滤波项的分布增益非线性薛定谔方程,模拟研究了短脉冲在有限增益带宽指数增益光纤放大器中的自相似演化行为及其差异。结果表明脉冲在不同指数增益分布放大器中传输时都会受到增益带宽的限制。相同输入脉冲在相同长度、相同总增益的指数上升、下降和双向分布放大器中放大时,在双向分布放大器中输出能量最高,输出脉冲线性啁啾特性最好,指数下降放大器输出能量最低,输出脉冲线性啁啾特性最差,指数上升放大器居两者之间。另外,总增益相同时,无论是指数上升、下降和双向分布放大器,初始增益系数较小,输出脉冲能量较高,脉冲线性啁啾特性较好。     

Analysis of stacked microstrip patches with a mixed potentialintegral equation

A method based on the mixed potential integral equation for the analysis of flat microstrip antennas in a double-layer substrate is presented. The method is used to compute the input impedance of a stacked patch configuration. This structure permits a larger bandwidth and may also provide dual-frequency operation. The Green's functions are discussed in detail, and numerical results are obtained for the propagation constant of the dominant surface wave. Theoretical and experimental results are compared for a dual-frequency and a broadband stacked patch antenna. Theoretical results for the input impedance are in good agreement with measurements. The difference between theoretical and experimental results for the resonant frequency is less than 4.5% in all cases     

A Switching Logic Digitizer for Analog-to-Digital Conversion

The design and simulation of a complementary output switching logic (COSL) compatible, voltage state, switching logic comparator (SLC), and a flash analog-to-digital converter (ADC) for high-speed applications, with multigigahertz input bandwidth, is presented. A detailed design for the SLC is provided and verified with simulations. The comparator is then optimized utilizing Monte Carlo yield predictions. The optimized comparator is incorporated into the construction of a 4-bit quantizer of an ADC. The Gray-code output is converted into binary using COSL gates. The functionality, linearity, maximum input bandwidth, and dynamic range of the 4-bit ADC is verified by simulation, using a number of special input waveforms. The performance of the comparator and the 4-bit ADC are also evaluated with thermal noise incorporated into simulations. Beat frequency simulations and Fourier spectra are also used in the evaluation of the ADC performance. A fully functional 4-bit ADC, with a maximum input bandwidth of 10 GHz for a clock speed of 20 GHz, was achieved through simulations. Beat frequency simulations revealed that the comparators have an input bandwidth greater than 19 GHz with sufficient dynamic range for an ADC of greater than 6 bits of resolution. Due to the fact that the aperture time for the ADC is dependent on the rise time of the sampling pulse and not the width of the pulse, a much smaller aperture time is obtained which directly translates to higher input bandwidth.     

Cavity length detuning characteristics of the synchronously mode-locked CW dye laser

We present both theoretical and experimental details on the effects of cavity length deturning of the synchronously mode-locked CW dye laser. The theory predicts an increase in cavity length sensitivity with intracavity bandwidth, and an asymmetric variation in the pulsewidth and pulse power with length detuning from the "matched" position. The predictions are shown to be in close agreement with the results of our experiments on the Rhodamine 6G dye laser.