特高频率测量新技术的研究

特高频率的测量是频率测量中的难点之一.所有针对特高频率测量最基本的方法都是建立在对频率信号处理的基础上,而最常用的处理方法是混频或谐波混频的方法.在利用该方法测量特高频率时是非常困难的,因为对高频进行倍频或分频是十分困难的,从而也就造成了特高频测量的主要困难.有人利用示波器实现了大频率比(105)的比对测量.该文对这种比对测量的方案做了进一步的分析,通过研究分析以及实验验证,指出了一种特高频测量的新思路.即采用变换测量的方式,将对很难测量的特高频的测量转变成对一种与之有一定对应关系且便于测量的对应量的测量.设计了一种对THz进行测量的原理框图,并对其做了分析说明.     

新型压电行走机构的振动模态分析

利用自行研制的浮动式压电振动机构,运用有限元分析软件ANSYS对机构振动模态进行了有限元分析发现,不同的工作频率其振动模态不同.当工作频率为934 Hz时,机构出现向前的滑移动或倒移动;工作频率为670 Hz时,在2个驱动足的底部形成"局部椭圆运动",机构向前移动;工作频率为1 176 Hz时,机构为向前滑移动或跳移动;工作频率为327 Hz时,机构出现侧移动或原地扭动;工作频率为498 Hz时,机构原地转动.这些理论上的分析对实际过程中的应用起到了一定的指导作用.     

Radio Signals with Large Relative Bandwidth for Over-the-Horizon Radar and Spread-Spectrum Communications

It is known that radio signals must have a small relative frequency bandwidth if structures and circuits resonating with sinusoidal functions are to be used for radiation and reception. This paper develops concepts showing that a small relative frequency bandwidth is also required for the use of amplitude or frequency modulation of sinusoidal radio carriers in the usual form. However, it is easy to modify the usual methods of amplitude and frequency modulation for signals with large relative frequency bandwidth. The primary application of such methods is for over-the-horizon radar and spread-spectrum communications in the short-wave region where the desired relative frequency bandwidths are neither small (in the order of 0.01 or less) nor close to 1.     

Errors in frequency parameters of EMG power spectra

Frequency shifts in random signals, e.g., EMG or Doppler ultrasound, can be followed by monitoring one or more parameters of the power spectrum. When such a frequency parameter is determined over a finite length of the signal, a random error and sometimes a systematic error or bias are introduced. Approximate expressions, in terms of moments of the power spectrum, have been derived for bias and standard deviation of the estimates for mean frequency, zero-crossing frequency, and fractile frequency (of which the median frequency is a special case). Experimental results from surface EMG recordings of three human muscles in constant force isometric contractions were in agreement with the theoretical predictions. In this case the mean frequency had the smallest random error. It turned out that the measured values of the zero-crossing frequency can deviate considerably from the predictions by the Rice formula when the amplitude distribution is not exactly Gaussian. In the presence of noise, all frequency parameters show a systematic deviation, depending on the signal-to-noise ratio. In addition to known results on this deviation for mean and zero-crossing frequency, an exact and an approximate expression for the fractile frequency are given. In the case of EMG plus wide-band white noise, the median frequency has the best immunity to noise.     

A novel frequency estimator for sampled Doppler signals

In multigate pulsed Doppler systems with serial processing the Doppler signals are retained in their sampled form. The time-discrete nature of the Doppler signals affects the procedure to estimate the average frequency of the Doppler signal. Based on computer simulation studies it is demonstrated that a time-discrete frequency estimator based on either the density of zero-crossings or the time average of the instantaneous frequency exhibit a large relative error under poor signal-to-noise conditions or in the case of relatively wide band signals. Especially, the frequency estimator based on the instantaneous frequency functions poorly for average Doppler frequencies close to the Nyquist frequency. However, restricting the detected instantaneous frequency to a specific interval around its average improves the estimator performance considerably, while it allows tracking of center frequencies beyond the Nyquist frequency. A hardware realization of this modified estimator as incorporated in a high-resolution multigate pulsed Doppler system is described. In vitro and in vivo registrations as assessed with this system demonstrate the ability of the system to track frequencies close to and beyond the Nyquist frequency.     

国际本地网络频率分配和监管框架研究

随着5G和工业互联网发展,世界上主要的工业制造发达国家都针对工业互联网快速增加的频率需求给出应对频率方案,针对工业4.0和垂直行业分配一定专有频率,用于部署本地网络.本地5G网络频率监管是一种新型的、灵活的、更加精细化的频率管理方式.对当前的国际本地网络频率分配以及监管框架进行梳理,主要调研各个区域和国家已经分配或者正...     

Posttuning Drift of a Transferred-Electron-Device Voltage-Controlled Oscillator (Short Papers)

An experimental study was done on the parameters affecting the frequency drift of a transferred-eletron-device (TED) controlled oscillator (VCO) after tuning from one frequency to another within its tuning band. For the VCO measured, reduction in frequency drift was observed and measured when: 1) the output power was reduced voltage either by decoupling the load or by using a lower power TED; 2) the voltage swing was restricted so as to draw less than 10 mu A forward or reverse current; and 3) when a varactor with a high Q was used. With 5-mW output the TED VCO had a frequency drift less than 2.5 MHz from 1 mu s to 100 ms when step tuning the frequency anywhere in the frequency band from 6.8 to 9.1 GHz.     

Blind self-noise-free frequency detectors for a subclass ofMSK-type signals

Frequency offset due to Doppler shift and/or oscillator instabilities degrade the receiver performance. A family of frequency detectors for frequency offset estimation and compensation in digital receivers is introduced. The proposed detectors are best suited for frequency offset compensation of a subclass of binary continuous phase modulation with h=1/2 that includes modulation schemes with nonnegative frequency pulses. For the considered modulation schemes, the modulation-induced self-noise term is absent from the variance of the frequency estimate. The estimator is nondata- and nontiming-aided and its estimation range is either half or a quarter of the bit rate (R). With larger frequency offsets, the estimators that have a ±R/2 estimation range introduce a frequency ambiguity of R that is of no relevance to the performance of a differential detection based receiver     

微波变频组件杂散信号分析与抑制设计

微波变频组件是通过一次或多次变频将微波信号变频至所需频率的器件,在变频过程中生成所需信号的同时也会混频产生多余的频率分量,这些频率分量对所需信号构成杂散信号必须予以抑制。基于降低杂散信号对输出信号的影响阐述了变频原理,具体分析了射频信号和本振信号混频后的频率分量,最后给出了一种变频组件的实现方法,实现了抑制杂散信号分量的目的。     

布里渊增益谱特征参数提取准确性影响因素分析

基于实测布里渊（Brillouin）增益谱确定了合适目标函数。数值产生了大量的布里渊增益谱,利用这些谱信号系统研究了信噪比、扫频间隔、扫频点数、扫频范围和谱特征参数g0、vB、△vB的取值对布里渊增益谱特征参数提取准确性的影响规律。结果表明:特征参数提取误差随信噪比增加成指数规律下降,随扫频点数增加（或扫频间隔减少）而下降;vB的提取误差随△vB的增加而线性增大,△vB的值对其他参数的提取准确性几乎无影响;扫频点数固定时扫频范围选择太大或太小时的误差均较大,实际应该选择2△vB左右。研究结果对基于布里渊散射的传感时相关参数选择具有参考价值。     

Ka 波段应用的捷变频高频率分辨率频率合成器

传统基于锁相环(PLL)实现带宽信号输出的频率合成方案,常常为了获得高输出频率而降低频率分辨率和缩短跳频时间。相较而言,基于直接数字频率合成器(DDS)实现带宽信号输出的频率合成方案,其频率分辨率更高,跳频时间更快。然而,DDS 输出频率低,须经多次混频或倍频操作以提升输出频率,对频率源中的滤波器设计造成极大压力,并且这种压力随着频率源输出频率的升高而不断上升。对此,基于高性能、小型化无源滤波器的设计能力,实现了基于DDS 变频的34-35GHz 捷变频、高频率分辨率频率源。实验结果表明,其工作相位噪声优于-85dBc/Hz@1kHz,杂散和谐波抑制优于45 dBc,频率分辨率达到1.86Hz,跳频时间最快4ns。     

Synthesis of the frequency response of a resistive strip with a piecewise constant profile

A new approach is proposed here to synthesize a desired frequency response of a resistive strip with a piecewise constant resistive profile. The strip can be attached at both ends to resistive (with constant resistance) or perfect electric conducting half-planes. The main feature of this method is the use ofutd solutions for the scattered field in a cost function which depends on the desired frequency response. The cost function is minimized by an iterative numerical scheme to determine the piecewise constant resistive profile. The scattered field in the frequency or spatial domains is then calculated usingutd or method of moments techniques. Several examples are shown for a Chebyshev frequency response.     

Waveform Selective Surfaces

The role of frequency is very important in electromagnetics since it may significantly change how a material interacts with an incident wave if the frequency spectrum varies. Here, a new kind of microwave window is demonstrated that has the unique property of controlling transmission and reflection based on not only the frequency of an incoming wave but also the waveform or pulse width. This is achieved by designing a planar periodic surface with circuit elements including diodes, which convert most of the incoming signal to zero frequency. This surface can preferentially pass or reject different kinds of signals, such as short pulses or continuous waves, even if they occur at the same frequency. Such a structure can be used, for example, to allow long communication signals to pass through, while rejecting short radar pulses in the same frequency band. It is related to the classic frequency selective surface, but adds the new dimension of waveform selectivity, which is possible only by introducing nonlinear electronics into the surface. Thus, the study is expected to provide new solutions to both fundamental and applied electromagnetic issues ranging from traditional antenna design and wireless communications to emerging areas such as cloaking, perfect lenses, and wavefront shaping.     

一种改进型增强图像处理算法研究与应用

常规的基于高斯或拉普拉斯模板的锐化或增强算法应用中,都会出现包边的现象,即在与邻域有强烈对比的目标上会出现明显的暗或亮包边问题。常规方法未对该现象进行处理,导致部分场景目标存在明显的包边现象。基于常规算法产生的包边问题的原因分析,发现主要是在获取高频图像信息时,采用高斯或拉普拉斯这种基于位置差异计算权重的方式导致；因此在进行获取高频细节时,通过增加以灰度差值来调整权重方式来获取细节,或采用更简单的高频细节截止的处理方式,可有效改善增强算法中的包边问题。     

A transmit MIMO scheme with frequency domain pre-equalization for wireless frequency selective channels

In this paper, we introduce a transmit multiple-input multiple-output (MIMO) scheme with frequency domain pre-equalization for a multipath or frequency selective channel. In this scheme, MIMO processing in the frequency domain is performed at the transmitter or base station so that the receiver or mobile station only requires limited processing. This scheme provides high data rates and also inherits from the frequency domain equalization the property of relatively low complexity in severe multipath environments. The MIMO transmit processing is derived by minimizing the minimum mean square errors (MMSE), and expressions for the signal-to-interference-plus-noise ratio and error probability based on the Gaussian approximation of the interference term are provided. Some important associated issues, such as channel errors and computational complexity, are also investigated. Numerical simulations are also provided and these demonstrate the improved performance of our proposed scheme compared to other transmit MIMO schemes. In particular, they show that the proposed system can attain multipath or frequency diversity of the channel.     

对数线性调频频控阵双基站探测系统

频率分集阵列又称频控阵(FDA),具有距离和角度依赖性。在FDA 中使用线性调频可以通过增大带宽来提高定位效果,但依然存在FDA 方向图的能量汇聚的周期性特点。合理使用非线性的频率增量或阵元间距可以破坏FDA 原有的周期性(如距离周期性),在定位目标时可以更加准确。文中提出一种频控阵与线性调频技术、对数非均匀频率增量相结合的发射波束形成方式,使用双基站进行收发定位,与常规频控阵及对数增量频控阵两种体制的双基站收发方向图进行了对比,说明其具有更好的定位单目标及多目标的效果。     

混合式频率合成技术在提高频谱纯度与扩频速度上的应用研究

单纯的DDS技术在与PLL技术在频率合成应用中各有优缺点，采用混合式频率合成技术可以将两者结合，做到取长补短。利用DDS激励PLL混合式频率合成技术实现了一种频率纯度较高、可快速数字扩频的频率合成器，并对设计过程中的问题进行了讨论。得到了优于传统技术的测试结果和频谱图。     

Memory-controlled frequency divider for fractional-N synthesisers

A new programmable frequency divider technique based on the memory-control of a prescaler is presented. It is particularly suited to FPGA or PLD implementations and for use in conjunction with stored-sequence or other fractional-N frequency synthesiser architectures     

基于精细化频带的脑磁信号跨频耦合特征分析

脑信号跨频耦合现象与人的意识活动密切相关。本文将精细化的频带划分方法和多种跨频耦合的度量方法相结合,研究不同类型手腕运动的脑磁信号跨频耦合特征。首先对四类手运动脑磁信号进行精细化的频带分解,采用了三种具有主次关系的耦合度量方法（相干、虚部相干、调制指数）,在高频耦合低频、低频耦合高频两种耦合形式下对某一运动方向类型信号显著区别于其它运动方向类型信号的频带数、通道对、频带对进行了统计分析,可以区分出不同方向手腕运动的MEG信号;进一步利用通道间的频带耦合关系以及源频带及其激励通道与响应通道等概念,采用相干耦合度量方法对上述两种耦合形式下的统计结果进行分析,获得相应的源频带、激励通道、响应通道,从而可以更加有效地区分不同方向手腕运动的MEG信号。      

Practical consideration for bandpass sampling

The uniform bandpass sampling theorem has been modified to cope with sampling frequency instability and carrier frequency variations. Minimum sampling rates for given sampling and carrier frequency variations are derived. A robust bandpass sampling method is proposed which requires the sampling frequency to be such that the carrier frequency is on the 1/4 or -1/4 sampling frequency grid