基于Agilent 86100取样示波器的时域网络分析系统

本文根据Nose-to-Nose校准技术的基本原理，提出了利用NTN技术和Agilent86100取样示波器，构建时域网络分析系统的新方法。该方法成功地实现了对标称带宽50GHz的同轴适配器、同轴电缆等器件的测量。通过数字信号处理不仅可以得到这些器件的全部时域特性（冲激响应、阶跃响应、上升时间和过冲等），而且还能得到其全部频域特性（幅频特性、相频特性和带宽等）。扫频源比对实验证明该方法是有效的。     

Broadband electron spin resonance at low frequency without resonant cavity

We have developed a nonconventional broadband electron spin resonance (ESR) spectrometer operating continuously in the frequency range from 0.5 to 9 GHz. Dual antenna structure and the microwave absorbing environment differentiate the setup from the conventional one and enable broadband operation with any combination of frequency or magnetic field modulation and frequency or magnetic field sweeping. Its performance has been tested with the measurements on a 1,1-diphenyl-2-picrylhydrazyl (DPPH) sample and with the measurements on the single molecular magnet, V6, in solid state at low temperature.     

一种长周期的宽带任意波形发生器

描述了一种基于直接数字波形合成(DDWS)技术的长周期宽带任意波形发生器(AWG)。采用PC机内存常用的超大容量高速缓存SDRAMMODULES来实现输出信号的长周期,采用内部具有双路数据分时切换结构的D/A实现输出信号的宽带,采用一片CPLD完成整个系统的时序逻辑控制。还给出了一个实际的AWG系统及其输出信号的测试结果。     

堆叠型太赫兹通信透镜天线设计

为了提高太赫兹通信天线的增益和定向性,提出了"井"字堆叠型透镜天线。该透镜天线工作在太赫兹第一大气传播窗口内,由初级馈源天线和透镜两部分构成。设计了角锥喇叭天线作为透镜天线的初级馈源;根据菲涅耳-基尔霍夫衍射理论和傍轴近似条件设计了"井"字堆叠型透镜用于聚焦太赫兹波,并分析了透镜结构在平面波入射时的聚焦场分布。利用控制变量法分析了透镜天线的全波周期和焦径比等结构参数对其远场辐射性能的影响。对所设计的透镜天线进行了实物加工和测试。实验结果表明:"井"字堆叠型透镜天线的加工和组装工艺简便,具有对称的辐射模式,在320~380GHz的工作频段内的增益高于26.4dB,3dB主瓣宽度低于4.8°,基本满足太赫兹通信系统对天线的高增益和强定向性等要求。     

Ultrafast time-domain spectroscopy based on high-speed asynchronous optical sampling

High-speed asynchronous optical sampling (ASOPS) is a novel technique for ultrafast time-domain spectroscopy (TDS). It employs two mode-locked femtosecond oscillators operating at a fixed repetition frequency difference as sources of pump and probe pulses. We present a system where the 1 GHz pulse repetition frequencies of two Ti:sapphire oscillators are linked at an offset of Deltaf(R)=10 kHz. As a result, their relative time delay is repetitively ramped from zero to 1 ns within a scan time of 100 micros. Mechanical delay scanners common to conventional TDS systems are eliminated, thus systematic errors due to beam pointing instabilities and spot size variations are avoided when long time delays are scanned. Owing to the multikilohertz scan-rate, high-speed ASOPS permits data acquisition speeds impossible with conventional schemes. Within only 1 s of data acquisition time, a signal resolution of 6 x 10(-7) is achieved for optical pump-probe spectroscopy over a time-delay window of 1 ns. When applied to terahertz TDS, the same acquisition time yields high-resolution terahertz spectra with 37 dB signal-to-noise ratio under nitrogen purging of the spectrometer. Spectra with 57 dB are obtained within 2 min. A new approach to perform the offset lock between the two femtosecond oscillators in a master-slave configuration using a frequency shifter at the third harmonic of the pulse repetition frequency is employed. This approach permits an unprecedented time-delay resolution of better than 160 fs. High-speed ASOPS provides the functionality of an all-optical oscilloscope with a bandwidth in excess of 3000 GHz and with 1 GHz frequency resolution.     

基于STM32与FPGA的数字示波器设计

为实现高采样率、宽频带的数字示波器,设计了以STM32和FPGA为控制核心的数字示波器。硬件平台主要采用了AD603电压程控增益放大器作为前端信号调理电路,ADS830高速宽带模数转换器和IDT7208高速缓存作为数字采集电路,以Labview界面显示。另外,通过采用自适应频率采集处理算法采集和还原信号波形。经实验测试,性能达到设计要求。     

67 GHz宽带谐波相位参考及其定标技术

作为非线性矢量网络分析仪的重要参考测量通道,谐波相位参考能够提供多频点、多波量以及复频率下的绝对相位测量能力。设计了基于共面波导非线性传输线方案的原型谐波相位参考样机,并提出了基于EOS光电采样系统的完整谐波相位参考定标技术,主要包括时基失配、平均去噪、相位对准、连接器失配与示波器复频率响应修正等流程。定标实验结果表明,原型样机能够在1 GHz功率27 d Bm信号激励下输出半峰值脉宽为22 ps的周期脉冲序列,其频带覆盖范围超过67 GHz,并在超高次谐波频点上拥有小于±10°的相位精度与小于±5°的相位可重复性。最后将原型样机装配到非线性矢网中,通过测量2 GHz信号激励下超窄时域脉冲发生器的输出时域信号,并将之与采样示波器测量结果进行比对,结果证实了谐波相位参考设计与定标技术的有效性与正确性。     

含氮固体物质的核四极共振远程探测仪

本文介绍一台结构简单，造价低廉的１４Ｎ核四极共振远程探测仪。它利用脉冲傅立叶变换技术，将获得的核自由感应衰减信号或回波信号进行相干累加以提高信噪比。整个系统分硬件和软件两部分。前者由射频脉冲放大器（有效值功率输出约３００Ｗ）、探头、接收机和ＩＢＭ—ＰＣ机构成。后者由ＰＣ机上的脉冲序列程序和数字信号处理程序组成。利用这台谱仪，能够在几十秒时间内得到距离探头线圈１０厘米以内的典型含氮化合物的核四极共振谱     

Repetitive sub-gigawatt rf source based on gyromagnetic nonlinear transmission line

We demonstrate a high power repetitive rf source using gyromagnetic nonlinear transmission line to produce rf oscillations. Saturated NiZn ferrites act as active nonlinear medium first sharpening the pumping high voltage nanosecond pulse and then radiating at central frequency of about 1 GHz: shock rise time excites gyromagnetic precession in ferrites forming damping rf oscillations. The optimal length of nonlinear transmission line was found to be of about 1 m. SINUS-200 high voltage driver with Tesla transformer incorporated into pulse forming line has been designed and fabricated to produce bursts of 1000 pulses with 200 Hz repetition rate. A band-pass filter and mode-converter have been designed to extract rf pulse from low-frequency component and to form TE(11) mode of circular waveguide with linear polarization. A wide-band horn antenna has been fabricated to form Gaussian distribution of radiation pattern. The peak value of electric field strength of a radiated pulse at the distance of 3.5 m away from antenna is measured to be 160 kV/m. The corresponding rf peak power of 260 MW was achieved.     

示波器的发展与合理选择

结合工作实践,介绍模拟示波器、数字存贮示波器、数字荧光示波器等三代示波器的概念、结构、工作原理及其特点,针对影响示波器价格的多种因素,如带宽、采样速率、内存深度等,讨论示波器的合理选取方法。针对第三代数字荧光示波器的应用特点,展望示波器的发展趋势。     

An Instrument for Measuring the Frequency Content of High-Power Nanosecond Microwave Pulses

An instrument for measuring the frequency content of single high-power nanosecond S-band microwave pulses was developed and tested. The measurement technique is based on the comparison of microwave signals arriving from two frequency-dependent channels with the use of a digital oscilloscope, a personal computer (IBM PC), and the MathCad software package. The meter allows one to record the spectrum and time variation of the carrier frequency of the radiation of a vircator-type relativistic oscillator in a frequency band of 2.7–3.7 GHz.     

Intermediate frequency band digitized high dynamic range radiometer system for plasma diagnostics and real-time Tokamak control

An intermediate frequency (IF) band digitizing radiometer system in the 100-200 GHz frequency range has been developed for Tokamak diagnostics and control, and other fields of research which require a high flexibility in frequency resolution combined with a large bandwidth and the retrieval of the full wave information of the mm-wave signals under investigation. The system is based on directly digitizing the IF band after down conversion. The enabling technology consists of a fast multi-giga sample analog to digital converter that has recently become available. Field programmable gate arrays (FPGA) are implemented to accomplish versatile real-time data analysis. A prototype system has been developed and tested and its performance has been compared with conventional electron cyclotron emission (ECE) spectrometer systems. On the TEXTOR Tokamak a proof of principle shows that ECE, together with high power injected and scattered radiation, becomes amenable to measurement by this device. In particular, its capability to measure the phase of coherent signals in the spectrum offers important advantages in diagnostics and control. One case developed in detail employs the FPGA in real-time fast Fourier transform (FFT) and additional signal processing. The major benefit of such a FFT-based system is the real-time trade-off that can be made between frequency and time resolution. For ECE diagnostics this corresponds to a flexible spatial resolution in the plasma, with potential application in smart sensing of plasma instabilities such as the neoclassical tearing mode (NTM) and sawtooth instabilities. The flexible resolution would allow for the measurement of the full mode content of plasma instabilities contained within the system bandwidth.     

A Computer-Controlled Magnetic Resonance Spectrometer with a Pulsed Magnetic Field

An automatic magnetic resonance spectrometer with a pulsed magnetic field is described. It has the following characteristics: a field range of 0–100 kOe, a frequency band of 25–140 GHz, a temperature range of 4.2–300 K, and a pulse duration of 12.6 ms. The spectrometer is automated to the CAMAC standard using standard modules. To record a magnetic-resonance spectrum, the following procedure is applied: the resonance-absorption signal is determined by a 10-bit analog-to-digital converter, and the magnetic filed is scanned by simulating a current pulse in a discharge circuit of the solenoid using a single input parameter—the initial charge voltage of the capacitor bank. In calibration measurements performed with spherical yttrium–iron-garnet samples, the average measurement error was 0.15%.     

Cutoff probe using Fourier analysis for electron density measurement

This paper proposes a new method for cutoff probe using a nanosecond impulse generator and an oscilloscope, instead of a network analyzer. The nanosecond impulse generator supplies a radiating signal of broadband frequency spectrum simultaneously without frequency sweeping, while frequency sweeping method is used by a network analyzer in a previous method. The transmission spectrum (S21) was obtained through a Fourier analysis of the transmitted impulse signal detected by the oscilloscope and was used to measure the electron density. The results showed that the transmission frequency spectrum and the electron density obtained with a new method are very close to those obtained with a previous method using a network analyzer. And also, only 15 ns long signal was necessary for spectrum reconstruction. These results were also compared to the Langmuir probe's measurements with satisfactory results. This method is expected to provide not only fast measurement of absolute electron density, but also function in other diagnostic situations where a network analyzer would be used (a hairpin probe and an impedance probe) by replacing the network analyzer with a nanosecond impulse generator and an oscilloscope.     

数字荧光示波器1.2GHz带宽前置放大器设计

本文介绍了数字荧光示波器1.2GHz带宽前置放大器的设计方法。首先介绍了系统的总体设计,然后给出了各个模块的设计,主要包括无源衰减网络的设计、阻抗变换网络的设计以及数控增益放大器的设计这三个部分。经过分析证明,该前置通道放大器实现了示波器基本功能,各项功能均能达到指定要求。与传统前置模拟通道放大器相比,该模拟通道放大器具有更高的带宽、更小的插入损耗等优点。     

A digital method for pulse-shape discrimination between particles

Results from experimental and theoretical investigations of a digital technique for pulse-shape discrimination are presented. Pulses from a scintillation (stilbene-based) detector are recorded by a digital oscilloscope and transmitted to a computer for carrying out particle identification. For a stilbene scintillation detector irradiated by neutrons and γ rays, the γ-ray suppression factor is ～0.5 × 10³?10⁴ and the neutron identification efficiency is ～0.70-0.90 over an energy range of ～30–500 keV at a counting rate up to ～10⁵ pulse/s. It is shown that this technique can form the basis for developing a detector unit that comprises a fast ADC and a digital signal processor and provides online identification of particles by scintillation pulse shape.     

Ground-based microwave spectroradiometer for thermal sounding of the troposphere

The laboratory model of a mobile solid-state uncooled microwave spectroradiometer, operating in the frequency range of 50 to 55 GHz is described. It is designed for remote passive monitoring of the tropospheric temperature. The spectroradiometer consists of a heterodyne receiver with a low noise amplifier at input and 8-channel spectrum analyzer. To ensure the internal calibration of the intensity of the received atmospheric radio emission using the built-in unit type modulator-calibrator based on GaAs diodes with the Schottky barrier. The antenna system of the spectroradiometer consists of a teflon enlightened lens and conical corrugated horn. The device is equipped with an automated control system process measurement, calibration, and data pre-processing.     

基于结构合成法的微型化双频WLAN印刷天线设计

针对当前WLAN技术的快速发展和已有的双频WLAN印刷天线存在增益不足、带宽较窄、尺寸偏大、制作成本高等缺陷的现状,本文借鉴了传统倒F印刷天线和蛇形单极子印刷天线的设计经验,提出了一种新的双频印刷天线设计方法,即结构合成法,并采用该方法设计了一种应用于IEEE 802.11a标准和IEEE 802.11b标准、占用面积仅13.6 mm×9.3 mm的新型微型化双频WLAN印刷天线。采用Ansoft HFSS对比研究了合成前后单频天线和双频天线的性能变化情况,并对双频天线的主要结构进行了分析和优化。仿真结果表明,天线在2.45 GHz和5.45 GHz两个谐振频点上的最高增益分别达2.74 d Bi和2.44 d Bi,相对带宽分别为15.5%和10.6%。此外,文中采用矢量网络分析仪对天线实物进行了测试,实测结果与仿真结果吻合,天线在低频和高频的谐振频点分别为2.53 GHz和5.71 GHz,S11-10 d B的有效带宽分别超过了400 MHz和500 MHz,展现出了良好的带宽特性。     

Variable resolution capability for multichannel filter spectrometers

In this paper we describe a new electronic instrument called a spectrum expander, which is a two-port digital signal-processing device whose output power spectrum Sout(f) is (approximately) a frequency-expanded replica of its input spectrum Sin(f): Sout(Ef) approximately Sin(f), where E is the expansion ratio (usually E>2). When inserted between a signal source and a spectrometer, the spectrum expander improves the effective resolution of the spectrometer, thereby permitting real-time, high-resolution measurements to be made. This capability is especially important in radio astronomy, where fixed-resolution multichannel filter spectrometers are common. Our treatment of the spectrum expander includes a discussion of its basic principles, formulation of design rules, a brief study of random noise and quantization effects, and presentation of data illustrating expander performance. The prototype expander, constructed from Schottky-TTL components, accepts any signal of bandwidth< or =12.5 MHz and expands it to fill a 128-channel spectrometer with 32-MHz total bandwidth. Signal degradation caused by processing with the spectrum expander is minimal; the signal-to-noise ratio at its output is measured to be approximately 0.1 dB lower than at its input.