单翼圆柱电磁散射的混合解

本文利用混合法分析和计算了单翼理想导电圆柱远场散射。这种混合法应用了物理光学近似（ＰＯ）、ＦＯＣＫ理论、物理绕射理论（ＰＴＤ）、几何绕射理论（ＧＴＤ）和矩量法。计算结果与矩量法和Ｍｉｃｈｅａｌｉ的计算和测量结果一致。与Ｍｉｃｈｅａｌｉ的方法相比，混合法对于任意尺寸的圆柱半径与翼宽和任意的入射角都适用。     

毫米波多单元线散射体的雷达散射截面计算

采用分域基（分段正弦函数）Ｇａｌｅｒｋｉｎ法计算了多散射单元一体化结构在８ｍｍ和３ｍｍ两个波段的雷达散射截面σ￣θ（散射角）曲线。结果表明：由于散射单元间的耦合作用,存在适当的结构形式,其雷达散射截面在毫米波段远大于单一谐振单元的散射效果;而且单元间间隙极小,具有较高的散射效率。     

基于NURBS曲面的目标电磁散射物理光学分析

随着计算机辅助设计与制造（CAD／CAM）技术的发展，非均匀有理B样条（NURBS）曲面被广泛应用于各种复杂物体（如：飞机、坦克、舰艇等）的设计与制造中。本文利用物理光学（PO）法，分析了由NURBS曲面构造的目标的雷达截面（RCS）．通过对NACA3317型机翼的计算机模拟，说明了本文的方法是有效的．     

基于积分方程的阵列信号的反演方法

本文将收敛速度快的变莆玻恩迭代法（ＤＢＩＭ）结合数值模式匹配法（ＮＭＭ）用于实际工程中的阵列感庆成象仪（ＡＩＴ）的测量的反演和剖面成象。在反演迭代过程中，利用ＮＭＭ解的Ｚ向解析性质，避免了双重数值积分，提高了计算效率，同时也提高了反演质量，文 中利用不完备的测量数据对ＡＩＴ进行了反演，表明该方法非常适合实际工程应用。     

裸地散射特性分析

本文详细地研究了裸地（农用耕地）的散射特性。根据实验现象提出了新的散射系数与入射角关系模型，与实验数据获得了很好的吻合性。通过分析裸地散射系数的雷达参数（入射角、极化、频率）和地面参数（粗糙度、土壤湿度）的响应特性，得到微波遥感土壤湿度时的最佳工作参数。     

一种有效的数值吸收边界条件与MEI方法的比较

本文给出了一种新的吸收边界条件，并与不变性测试方程法（ＭＥＩ）、矩量法在计算时间、存贮空间方面进行比较，结果表明运用这个条件在计算时间和存贮空间上都具有优点，是计算电大尺寸媒质柱体电磁散射特性的一种有效手段。     

三维大纵横比目标散射的快速精确求解

采用积分方程法严格求解三维大纵横比目标的电磁散射。在积分方程法的迭代求解中用快速我极子法（ＦＭＭ）加速矩阵与矢量的相乘计算,同时运用快速傅里叶变换（ＦＦＴ）进一步提高快速多极子方法中的转换预计算,数值结果表明：这种快速多极子法－快速傅立叶变换方法（ＦＭＭ－ＦＦＴ）特别适合于三维大纵横比目标的散射求解。     

布里渊散射在光纤拉伸应变分布测量中的应用

论述了布里渊散射测量光纤拉伸应变的原理,对近年来布里渊光时域反射计法（ＢＯＴＤＲ）和布里渊光时域分析技术（ＢＯＴＤＡ）的研究概况进行了评述,并提出了这些技术尚存的问题和可能的解决办法。     

N阶色散媒质的瞬态散射特性

本文提出了Ｎ阶色散媒质瞬态特性的时域分析方法，结合Ｚ变换对常规的时域有限差分（ＦＤＴＤ）法进行了修正，改进后的ＦＤＴＤ法能分析和与频率有关的电磁场问题，具有方法简洁、易实现等优点。为验证此方法的有效性和可靠性，对Ｎ阶色散媒质的反向系数进行了分析与计算，并与已知的解析结果进行了比较，同时，采用此时域方法对Ｎ阶色散媒质和导体覆盖Ｎ阶色散媒质散射场进行了计算和分析。     

计算腔体散射的GRE—FDTD混合方法

在飞机雷达截面（RCS）的理论预估中，飞机进气道的电磁散射计算是其难点之一。对于厘米波段雷达而言，进气道属于电大尺寸目标，而其终端一般还存在涡轮叶片之类的复杂结构，单用高频近似方法难以解决。本文介绍GRE－FDTD混合方法可用于进气道的电磁散射计算。该方法用广义射线展开法（GeneralizedRayExpansion，GRE）计算进气道前端的缓变部分，用时域有限差分法（FDTD）计算包括涡轮叶片的复杂结构段。计算结果与波导模式法（Modal）－炬量法（MoM）混合方法的结果相比较，二者有很好的一致性。     

一种雷达目标极点提取方法及极点特性的分析

散射物体复自然谐振频率(极点)是目标识别可以利用的一个重要特征。使用传统求解极点的方法,通常得到的极点数目比较多,并且存在TE、TM两种模式。因此,对极点的规律分析较多的是对其模式变化趋势的分析。这些特性对于极点的实际应用没有太大的意义。本文从频率矩量法得到的散射数据出发,提出了一种波形拟合的极点提取方法。以有限长柱和椭球为例。分析了极点与入射波模式、目标姿态的关系,得到有实际指导意义的结论。     

地物目标红外热像理论建模中的蒙特卡罗法与并行计算

蒙特卜罗法结合区域人解算法，求地物目标温度场和红外辐射出射度场，将三维复杂几何形体解为若干个规则的子区域，不同的子域选用不同的坐标系，用控制容积法分别处理，整体结构用热网络法，用蒙特卡罗法计算辐射传递系数，可考虑办面的复杂辐射特性，引入辐射传递系数，分离了计算的难点，并可小段并行处理，在空间域（计算区域）上将目标分解为若干个子域，也可使用多个处理器并行计算。     

基于OFDM循环前缀LS信道估计的构造方法

提出了一种在正交频分复用系统中循环前缀频域序列（CPFS）用于最小二乘信道估计的子载波构造方法。该构造方法基于比较CPFS序列和梳状子载波序列的相关性,可使LS信道估计的精度增加。该相关性利用凸优化的方法,以子载波总体为变量及LS信道估计的最小均方误差（MSE）机制建立约束,得到优化模型并通过拉格朗日方法求得最终构造解。仿真验证表明,该构造方法得出子载波新解能使得LS估计模型下,CPFS序列的估计精度更优。     

Novel Design Approach for X-Band GaAs Monolithic Analog 1/4 Frequency Divider

A novel analog frequency divider which can generate a 1/4 frequency component is proposed. The frequency divider consists of a dual-gate FET and a two-stage capacitor-resistor coupled amplifier. This circuit configuration also enables achieving a small-size GaAs MMIC analog frequency divider. In this analog frequency divider, the input signal f/sub 0/ is mixed with signal component f/sub 0//x caused by noise or transients in a feedback loop. Then, a (1 -- 1/x)f/sub 0/ IF component is induced and is again mixed with the input signal. This process delivers the f/sub 0//x component regeneratively. Resultant continuous signal components f/sub 0//x and (1-1/x)f/sub 0/ have a harmonic relation when the system reaches a steady state. The f/sub 0//x component can be mainly obtained at an output port of the frequency divider. The operation band was simulated using a SPICE II computer program. The designed bandwidth and conversion gain for the 1/4 frequency divider are 8.5-10.6 GHz and -3 dB, respectively. Based on the simulation, a GaAs monolithic analog 1/4 frequency divider was made and tested. The developed 1/4 frequency divider provides a 8.5-10.2-GHz operation bandwidth and --5+-1-dB conversion gain. The designed and experimental values are in good agreement. The frequency division band can be shifted to higher frequency (10.65-11.2 GHz) by adopting the external matching circuit at the GaAs chip output port. The proposed analog frequency divider circuit can be applied not only for 1/4 frequency division, but also for 1/n frequency division (interger n > 2).     

Fast algorithms for single frequency estimation

In this paper, some new estimators of the frequency of a single complex sinusoid are presented. The rotate-add-decimate (RAD) method of Crozier is first refined to more closely approach the Cramer-Rao Bound (CRB). An additional modification yields an unbiased estimator (ERAD) that essentially achieves the CRB above a signal-to-noise ratio (SNR) threshold comparable to that of RAD. In addition, this estimator is proven to achieve the CRB for high SNR. The ERAD method requires approximately 2N complex multiply-adds and log/sub 2/N arctangents. A modified ERAD (MERAD) is proposed that matches the SNR threshold and computational complexity of the RAD method (approximately 3N complex multiply-adds and log/sub 2/N arctangents) but achieves the CRB for high SNR.     

次随机分块PTS-Clipping峰均比抑制算法

针对正交频分复用信号存在高峰均比问题,本文提出了一种基于次随机分块的部分传输序列(partial transmit se-quence,PTS)与传统限幅剪切联合处理的峰均比抑制算法.该算法在时域得到随机分块的子块序列,子块序列乘以相位旋转因子得到多个备选序列,从多个备选序列中寻找低峰值OFDM信号,最后利用频域滤波剪切算法限幅.仿真结果表明,所提算法在低复杂度下可以有效降低PAPR.     

单芯双向通信的研究

介绍了实用化的单芯双向通信的基本方法 ,分析了波分复用 ( WDM)单芯双向通信方式并给出了指标要求。重点讨论了副载波 ( SC)单芯双向传输技术 ,通过在电域采用频分制技术解决自发自收问题 ,确定了方向滤波器技术指标。最后给出了采用副载波技术所实现的单芯双向传输系统的性能。     

Power spectrum analysis of the cross/intermodulation in the nonlinear LNA

This study deals with the effects of the cross/intermodulation (CM/IM) on the communication performance when both Tx (transmit) leakage and external single tone interference pass through LNA in code division multiple access (CDMA)/frequency division duplex (FDD) transceiver. The CM/IM powers happen because of the nonlinearity of the LNA and these get work as interference to the desired signal. The CM/IM interference powers are analyzed with the frequency change of external single tone interference in Rx (receive) band. The relationship between these interference powers, input third-order intercept point (IIP/sub 3/), and the dependence of the allowable noise figure (NF/sub allowable/) on the IIP/sub 3/ are presented in this study. If IIP/sub 3/ is large enough for CM/IM interference power spectrum slightly to overlap with the Rx band, the interference power in Rx band gets smaller but NF/sub allowable/ increases as IIP/sub 3/ is increased. Thus, the bit-error-rate (BER) performance is degraded. On the other hand, when the interference power spectrum largely overlaps with the Rx band, it is important to increase the IIP/sub 3/ to get the better BER performance since the performance improvement by the linearity growth is larger than the performance degradation caused by the increment of NF/sub allowable/.     

Approximation of SNR degradation due to carrier frequency offset for OFDM in shadowed multipath channels

We derive an approximate expression for signal-to-noise ratio (SNR) degradation of orthogonal frequency division multiplexing due to carrier frequency offset over a shadowed multipath channel, to explicitly show the effects of system and channel parameters on the degradation of the received SNR. The results show that, for small frequency offset, the SNR degradation is proportional to the square of the frequency offset and the square of the number of subcarriers. It is also shown that, if E/sub s//N/sub 0/ is reasonably large, the SNR degradation becomes insensitive to E/sub s//N/sub 0/, which is contrary to the case of the additive white Gaussian noise channel.     

Downlink transmission of broadband OFCDM Systems-part I: hybrid detection

The broadband orthogonal frequency and code division multiplexing (OFCDM) system with two-dimensional spreading (time and frequency domain spreading) is becoming a very attractive technique for high-rate data transmission in future wireless communication systems. In this paper, a quasianalytical study is presented on the downlink performance of the OFCDM system with hybrid multi-code interference (MCI) cancellation and minimum mean square error (MMSE) detection. The weights of MMSE are derived and updated stage by stage of MCI cancellation. The effects of channel estimation errors and sub-carrier correlation are also studied. It is shown that the hybrid detection scheme performs much better than pure MMSE when good channel estimation is guaranteed. The power ratio between the pilot channel and all data channels should be set to 0.25, which is a near optimum value for the two-dimensional spreading system with time domain spreading factor (N/sub T/) of 4 and 8. On the other hand, in a slow fading channel, a large value of the channel estimation window size /spl gamma/N/sub T/, where /spl gamma/ is an odd integer, is expected. However, /spl gamma/=3 is large enough for the system with N/sub T/=8 while /spl gamma/=5 is more desirable for the system with N/sub T/=4. Although performance of the hybrid detection degrades in the presence of the sub-carrier correlation, the hybrid detection still works well even the correlation coefficient is as high as 0.7. Finally, given N/sub T/, although performance improves when the frequency domain spreading factor (N/sub F/) increases, the frequency diversity gain is almost saturated for a large value of N/sub F/ (i.e., N/sub F/ /spl ges/ 32).