采用LMS算法消除开关电源对CDMA接收机的影响

研究了开关电源开关频率对CDMA接收机的影响,拟提高开关电源的应用领域。分析了开关电源的噪声及常用抑制噪声的方法。通过Simulink建立CDMA通信系统模型,以单频正弦为噪声干扰CDMA接收机,并利用自适应陷波器和LMS算法在接收机基带处进行处理。处理前后误码率、EVM值均有不同程度的下降。该方法为开关电源在射频领域的应用提供了基础,且具有良好的应用前景。     

应用渐近波形估计技术快速计算宽带雷达散射截面

将渐近波形估计技术应用到矩量法中,计算了任意形状二维理想导体目标的宽带雷达散射截面.计算中使用矩量法和奇异值分解技术求解电场积分方程,得到一展开频率点的表面电流密度,通过Padé近似求出给定频带内任意频率点的表面电流密度分布,进而计算出散射场和雷达散射截面.奇异值分解技术的使用消除了电场积分方程的内谐振问题.对数值计算结果与矩量法逐点求解的结果进行了比较,两者吻合良好,且计算效率提高了约一个数量级.     

Synthetic bandwidth method and experimental research based on a wideband multi-channel SAR

Synthetic bandwidth technique is used to increase frequency bandwidth of the system and provides an effective way to achieve the ultra high resolution in the field of Synthetic Aperture Radar (SAR). But in the actual SAR system, the synthesis result will be seriously deteriorated by the inner-channel and inter-channel phase error. A frequency domain synthetic bandwidth method based on transfer function extracting technique is proposed in an actual SAR system which consists of single wideband transmit channel and 8-way down-conversion receive sub-channels. The method can accurately get the amplitude and phase characteristics of the sub-channel and compensate the amplitude-phase errors. The final experimental results demonstrate the validity and feasibility of the method and the range resolution down to 0.1 m is obtained.     

凹球面双频聚焦超声声场的线性声学分析

在线性声学条件下,研究了差频相干模式下的双频聚焦声场的空间-时间特性,分析了换能器分割面积、不同频差对声场的影响.通过计算两波在不同初始相位时轴上瞬时声压起伏的周期性变化规律,证明其合成声场是统计平稳和均匀的.结果表明,适当选择分割面积比和频差,双频声场的"损伤声焦域"相对于单频有明显扩大,并在离体牛肝的损伤实验中得到初步验证,为双频高强度聚焦超声(HIFU)换能器的设计及提高治疗效率提供参照.     

Optical Millimeter-Wave Signal Generation Using Frequency Quadrupling Technique and No Optical Filtering

This letter demonstrates a novel method to generate high-purity optical millimeter-wave signals with carrier suppression by using a frequency quadrupling technique. To the authors' knowledge, this is the first time that a frequency quadrupling system requires only a single integrated Mach-Zehnder modulator without a narrowband optical filter to remove undesired optical sidebands. Since no optical filter is needed, fast frequency tuning is straightforward and this approach will be particularly attractive for optical up-conversion in wavelength-division-multiplexing radio-over-fiber systems. This letter provides both theoretical analysis and experimental demonstration. The generated optical millimeter-wave signals have very high quality with an optical carrier and harmonic distortion suppression ratio of more than 38 and 36 dB at 40 and 72 GHz, respectively.     

An aperture-matched compact range feed horn design

The moment method and the uniform geometrical theory of diffraction are used to obtain two separate solutions for theE-plane far field pattern of an aperture-matched horn antenna. This particular horn antenna consists of a standard pyramidal horn with the following modifications: a rolled edge section attached to the aperture edges and a curved throat section. The resulting geometry provides significantly better performance in terms of the pattern, impedance, and frequency characteristics than normally obtainable. The moment method is used to calculate theE-plane pattern and voltage standing-wave ratio (VSWR) of the antenna. However, at higher frequencies, the moment method requires large amounts of computation time. On the other hand, the uniform geometrical theory of diffraction provides a quick and efficient high frequency solution for theE-plane field pattern. In fact, the uniform geometrical theory of diffraction may be used to initially design the antenna; then the moment method may be applied to "fine tune" it. In both methods, a two-dimensionalE-plane model of the antenna is used, but these two-dimensional solutions yield excellent agreement with measured data of the actual three-dimensional antenna. This procedure has been successfully applied to design a compact range feed horn.     

应用于音频芯片的高精度ΣΔ调制器设计

低阶单比特量化ΣΔ调制器简单稳定且特别适用于音频领域的模数转换器。提出了一款应用于音频芯片的二阶单比特量化ΣΔ调制器,利用Simulink对调制器进行建模并确定调制器参数与电路子模块指标。该调制器电路采用CSMC0.35μmCMOS工艺实现,工作的电源电压为5V,采用全差分开关电容技术,功耗为12mW,核心面积为390μm×190μm。在采样频率为12MHz、输入信号频率为20kHz时,调制器精度达到16bit,测试结果验证了设计技术和建模方法。     

Broadband vibration control of a structure by using a magnetorheological elastomer-based tuned dynamic absorber

A passive dynamic vibration absorber (DVA) is a mass-spring system that suppresses the vibration of a structure at a particular frequency. The DVA is especially effective when its excitation frequency is close to its tuned frequency. Fixing the physical properties of the DVA limits the application to a narrowband, harmonically excited vibration problem. A frequency-tunable DVA that can modulate its stiffness provides adaptability to the vibration control device against non-stationary disturbances. In this paper, we suggest a broadband frequency-tunable DVA whose natural frequency can be extended to more than 300% of the base value by using magnetorheological elastomers. We first conducted a magnetic field analysis by using a finite element method, through which the formation of a strong magnetic field within the core was observed. By taking full advantage of the frequency adjustability of the proposed DVA, we evaluated the real-time vibration control performance for an acoustically excited plate having multiple resonant peaks. The results show that the vibration of the structure can be effectively reduced with an improved performance by using a DVA instead of a passive absorber.     

探地雷达频率域2.5维正演

该文从频率域电磁法满足的控制方程出发,采用有限单元法实现了频率域2.5维探地雷达(GPR)正演模拟。重点分析了波数域电磁场谱随相对介电常数和收发距变化的规律,探讨了2.5维GPR正演模拟的波数选取问题;基于Open MP并行算法与串行算法的计算效率对比,表明频率域2.5维GPR数值模拟方法具有高效率、高精度和高度并行性的特点,为雷达正演提供重要理论参考依据和技术支撑,是GPR全波形反演的重要基础。     

The Method of Series Expansion in the Frequency Domain Applied to Multidielectric Transmission Lines (Short Papers)

In this short paper a method of expanding the phase constant and the field of a multidielectric transmission line as a power series of the frequency is developed. The method provides a theoretical justification for the widely used "static" approximations and indicates the reason why their accuracy is frequently good. This expansion may also be useful for estimating an upper limit to the frequency band in which the dispersion does not exceed a specified value. A numerical example is included.     

Direct measurement of base drift field in bipolar transistors

The authors have developed a method to measure an effective base drift field and the base transit-time reduction factor of bipolar transistors, by measuring the excess phase of the base transport factor. This technique relies on measuring small-signal characteristics of the transistor at a low frequency and following the phase of the transconductance at the frequency approaching and exceeding the unit current gain frequency (f_T). With this technique, the authors verify that the effective drift inside the base of Si bipolar transistors decreases with increased base implantation energy and thermal treatment. Such directly measured drift-dependent base transport provides additional insight for optimizing processing used in bipolar technology development     

Velocity-matching techniques for integrated optic traveling wave switch/modulators

We propose and analyze a new technique for achieving velocity match between the traveling wave electrical drive and guided optical signal for modulators in substrates for which there is an inherent mismatch. The traveling wave electrodes are laterally shifted periodically to reverse the direction of the applied electric field within the optical waveguide which exactly compensates for the polarity reversal caused by the microwave-optical walkoff. Consequently, the electrooptically induced phase shifts of each section add in phase and several sections can be used to reduce the required drive voltage at the design frequency. This artificial velocity-matching technique moves the mismatch-limited bandwidth to an arbitrarily high design frequency. In addition, we extend the new concept of phase reversal and the previously suggested technique of intermittent interaction by proposing electrode structures with large inactive to active aspect ratios. This generalization provides increased flexibility for manipulating the total available bandwidth to, for example, allow efficient modulation by a train of arbitrarily short electrical pulses. These techniques are ideally suited for several proposed integrated optic devices, including picosecond samplers and gates, which require strong overmodulation at a single high frequency.     

未知衰落信道中MPSK信号的非数据辅助载波频率估计方法

未知衰落信道中的MPSK信号的非数据辅助载波频率估计是通信参数估计中的复杂问题,目前尚缺乏有效的针对性研究成果.针对该问题,提出采用先补偿信道影响,再去调制,然后进行非衰落信道单频信号频率估计的方法.该方法比进行频率和信道冲激响应联合估计的方法简洁和高效,而且解决了联合估计中难以有效去调制的问题.通过和非衰落信道的频率...     

基于FOLP的STBC-OFDM信号盲识别方法

针对STBC-OFDM信号盲识别中存在着识别所需样本数多、对频偏敏感和不适用于单接收天线等问题,提出一种基于FOLP（Fourth Order Lag Product）的识别方法.根据不同空时分组码元素的相关性,推导了接收信号的FOLP,构造了基于FOLP的峰值检测算法.推导和仿真结果表明,该算法能够在单接收天线下运行,且不需要知道信道信息、噪声信息、调制信息以及OFDM块的起始位置;且该算法不受调制方式的影响,对时延、相位噪声和频率偏移鲁棒性能好,能够应用于认知无线电、频谱监控等工程领域中.     

基于CFS-PML的高阶有限元在地质雷达数值模拟中的应用研究

为衰减地质雷达数值模拟时因截断区域厚度或者参数影响产生的倏逝波,提出了一种利用复频移完美匹配层(complex frequency shifted perfectly matched layer,CFS-PML)作为吸收边界,并结合频域高阶有限元算法（higher order finite element method,HO-FEM）求解电磁总场分量分布情况的新方法.该方法改善了截断域介质本构张量矩阵的特性,利用矩阵频移参量α吸收倏逝波,提高掠射角处吸收性能.数值实验结果表明,与传统PML相比,结合CFS-PML的HO-FEM方法精度得到明显提高,反射误差额外降低10～30 dB,节省了17%～30%的计算时间.此外,该方法能应用于复杂地质结构模型的电磁总场计算,为地质雷达数值模拟提供了一种新的方法.     

Multitone Feedback Through Demodulating Log Detector for Detection of Spurious Emissions in Software Radio

This paper provides an analysis of a log detector in order to determine its response to a multitone input for detection of spurious emissions in a radio frequency transmitter. Treatment is given to the single tone response of the log detector and extended to a two-tone log detector system, where a large signal and a small signal are present. The large signal is observed to experience logarithmic processing with an output at zero frequency. The small signal produces an output at the difference frequency of the large signal frequency and small signal frequency that is approximately proportional to the ratio of the small signal voltage to the large signal voltage. The two-tone results are generalized to an m-tone input. Experimental results are presented to show the accuracy of the model. The log detector circuit analyzed is able to detect a spurious emission within 45 MHz of the main signal with plusmn1 dB of accuracy.     

Application of the TLM method to half-space and remote-sensingproblems

The problem of scattering and radiation in the presence of a material half-space is solved using the transmission line matrix (TLM) method. The TLM method is a general numerical method for obtaining an approximate solution to the time-dependent form of Maxwell's equations in the presence of complex environments. The method requires the discretization of the entire spatial domain of the problem and provides the transient response as well as (through discrete Fourier transform) the frequency domain response. The three-dimensional symmetric-condensed TLM node is applied. A total/scattered field formulation is applied to excite the space. The source used is an electrically short electric dipole and is described analytically in the time-domain. The method is used to calculate near field distributions (in both the time and frequency domain) and the change in source input impedance of a dipole radiator in the presence of a half-space. Numerical simulations relevant to the detection of buried objects are provided     

Line Width and Bandwidth of Millimeter-Wave Resonance Isolators

A theoretical derivation is made of bandwidth as a function of resonant frequency of a single crystal ferrite resonance isolator at millimeter wavelengths. The derivation takes into account the ferrite isolator as a bounded system. Using the derived relation of bandwidth and resonant frequency, and Kittel's relation between resonant frequency and applied field, equations are derived which relate line width to resonant frequency, line width to the applied magnetic field, and line width to frequency bandwidth. These resulting equations are compared with experimental data obtained with a single crystal barium ferrite isolator from 58 to 59 kMc. The theoretical relations agreed closely with the experimental data within the accuracy of the measuring equipment at these frequencies. In general, the results showed that for small frequency ranges (1 kMc) bandwidth and line width increase almost linearly with frequency, bandwidth and line width are linearly related, and line width is a fairly complicated but increasing function of applied field.     

The simultaneous interpolation of antenna radiation patterns inboth the spatial and frequency domains using model-based parameterestimation

The Pade rational function fitting model commonly used for model-based parameter estimation (MBPE) in the frequency domain is enhanced to include spatial dependence in the numerator and denominator coefficients. This allows the function to interpolate an antenna radiated electric field pattern in both the frequency and spatial domains simultaneously, such that a single set of coefficients can be used to accurately reconstruct an entire radiation pattern at any frequency in the fitting-model range. A simple procedure is introduced for transforming interpolated electric fields into gain patterns using input impedance versus frequency curves also obtained via MBPE. The utility of this method is demonstrated by applying it to a dipole antenna over a frequency range of 150-950 MHz and using a polynomial representation in &thetas; for the coefficient spatial dependence. It is also used to estimate radiation patterns for a three-element Yagi array between the frequencies of 470 and 500 MHz using a binomial representation for the spatial variation that includes terms dependent on &thetas; as well as φ. The use of this method for interpolating radiation patterns has at least two significant advantages; one being large compression ratios for the amount of data that must be stored to accurately reproduce patterns and the other being a significant decrease in the amount of time required for modeling problems with large computational domains     

Analysis and Optimization of Leaky-Wave Radiation at Broadside From a Class of 1-D Periodic Structures

Radiation at broadside from leaky waves is studied for one-dimensional periodic structures modeled by means of a transmission line periodically loaded by series or shunt loads. Radiation at broadside occurs via an axially fast spatial harmonic in a neighborhood of the open-stopband frequency; operation in such a frequency range is studied here by means of an approximate asymptotic Bloch analysis of the adopted equivalent network and a simple array-factor calculation of the radiated far field. The condition of equal values for the phase and attenuation constants of the radiating spatial harmonic is shown to give rise to maximum radiation at broadside in the lossless case and to the splitting of a single peak of the radiation pattern at broadside into two distinct peaks in both the lossless and the lossy cases. The 3 dB frequency band for broadside radiation is characterized in terms of the leaky-pole locations in the complex plane and an approximate formula for the antenna bandwidth is provided. Numerical results illustrating these properties are provided, including full-wave simulations of a specific structure through the method of moments.