Procedure for phase discrimination applicable to homodyne reflectometers for plasma density measurements

A phase discrimination method for homodyne reflectometers applied to plasma density fluctuations is proposed and tested in the laboratory simulating the plasma fluctuations by a vibrating metallic mirror. Applicability conditions for plasma measurements are established. The method can be used in broadband operation. Application to density profile measurements is also possible.     

Six-port and four-port reflectometers for complex permittivitymeasurements at submillimeter wavelengths

The frequency range of six-port reflectometry is extended into the submillimeter wavelength range. The complex permittivity of low-loss microwave materials is determined using novel six-port and four-port reflectometers. These either consist of quasi-optical components or utilize oversized waveguide techniques. Permittivity measurements of materials possessing a wide range of values of ϵ' (2 to 7) and of the loss tangent (0.0003 to 0.03) were carried out at frequencies of about 380 GHz to 390 GHz. Good agreement with published permittivity data is shown. Moreover, the equivalance of the simple waveguide four-port reflectometer (which is preferred because of its easy handling and high stability against temperature fluctuations) to the quasi-optical reflectometers is shown     

A Novel Calibration Algorithm for a Special Class of Multiport Vector Network Analyzers

A new error model for a special class of multiport vector network analyzers (VNAs) is presented in this paper. This model can be applied to multiport network analyzers with noncomplete reflectometers, i.e., when the measurement of the incident waves at each port is not always available. The method used to compute the error coefficients proposed here is based on a compact and easy formulation. This method is an extension of the already existing general theory for complete reflectometer multiport network analyzers. Furthermore, the new error model generalizes the theory for three-sampler two-port VNAs. The proposed model has been tested against the complete reflectometer one and exhibits the same accuracy level.     

Application of microwave reflectometry for plasma density diagnostics in a reversed-field pinch machine

The implementation of reflectometry as a means of measuring plasma density is examined in relation to the reversed-field pinch machine. The effects of magnetic shear and density fluctuations are studied. Ray-tracing and simulation results are presented and the proposed reflectometer system for the RFX reversed-field pinch machine is described.     

The charactization of high-speed swept reflectometer for plasma diagnostics on the RFX reversed-field pinch

An ordinary mode IMPATT-based reflectometer operating over 26.5–110GHz has been developed for density diagnostic application on the RFX reversedfield pinch experimental fusion machine. The reflectometer uses polarization rotators located at the antennas for optimizing the polarization of the emitted E-field A sweep speed of 1.25ms for the full band is possible. Single subbands may be swept at a rate of 200us. The provision of polarization rotators and high-speed solid-state oscillators maximises the immunity of the system to the effects of high fluctuation frequencies and mode mixing due to high magnetic shear. The reflectometer uses an IMPATT oscillator system for the source which has not been used in previous reflectometer circuits. A previously unachievable temporal resulution is therefore available with this system. The reflectometer is the first to be developed for use on a reversed-field pinch (RFP) machine. Verification of reflectometer operation was achieved using plane metal targets to simulate the reflecting plasma cut-off layer. Targets were located at various distances from the antennas to cover the expected spatial reflection range. The theoretical and experimental characteristics were obtained by processing the intermediate frequency output of the detectors. Spurious signals are removed by calibrating the target data using residual fringe data. A zero-crossing detection algorithm was developed to accurately identify the beat fringes and to deduce the phase/frequency characteristic. Single subband and full sweep results are presented.     

非均匀等离子体包覆平板模型微波反射功率测量与分析

介绍了等离子体隐身技术的原理性试验。在大气环境中利用已有的微型固体火箭发动机作为等离子体发生器进行试验,控制发动机喷流流场中的电子密度分布,采用微波反射仪测量金属平板在有无以及不同电子密度喷流包覆情况下的微波反射功率。试验结果表明,峰值电子密度为1011 e/cm3的非均匀等离子体对9.5GHz的微波具有明显的吸收作用,并且试验结果和数值计算结果吻合较好。通过试验,验证了等离子体隐身的特性,为下一步开展等离子体隐身研究打下基础。     

Ten-channel coherent optical fibre transmission

A laboratory ten-channel coherent fibre-optic broadband transmission system is reported. The frequency-division-multiplexed optical carriers are separated by 6 GHz and are demultiplexed by a tunable heterodyne receiver having a sensitivity of -46 dBm at a bit error rate of 10-9. In this system a maximum number of 64 channels can be installed.     

A 0.18μm CMOS 3-5 GHz broadband flat gain low noise amplifier

A 3-5 GHz broadband flat gain differential low noise amplifier (LNA) is designed for the impulse radio uitra-wideband (IR-UWB) system. The gain-flatten technique is adopted in this UWB LNA. Serial and shunt peaking techniques are used to achieve broadband input matching and large gain-bandwidth product (GBW). Feedback networks are introduced to further extend the bandwidth and diminish the gain fluctuations. The prototype is fabricated in the SMIC 0.18 μm RF CMOS process. Measurement results show a 3-dB gain bandwidth of 2.4-5.5 GHz with a maximum power gain of 13.2 dB. The excellent gain flatness is achieved with ±0.45 dB gain fluctuations across 3-5 GHz and the minimum noise figure (NF) is 3.2 dB over 2.5-5 GHz. This circuit also shows an excellent input matching characteristic with the measured S11 below-13 dB over 2.9-5.4 GHz. The input-referred 1-dB compression point (IPldB) is -11.7 dBm at 5 GHz. The differential circuit consumes 9.6 mA current from a supply of 1.8 V.     

Mobile broadband system (MBS): trends and impact on 60 GHz bandMMIC development

The RACE mobile broadband system (MBS) project aims to extend the broadband integrated services digital network (B-ISDN) to mobile users. To meet the future demand for broadband wireless picocell networks, frequencies have been allocated in the 62-63 and 65-66 GHz bands. However, for the use of a mobile broadband system to become widespread it is necessary to develop relatively low cost transceivers based on millimetre wave GaAs P-HEMT MMICs. A transceiver architecture and elementary building blocks have been defined. 60 GHz transistor models have been refined and circuit design, layout and simulation achieved. Future cost decrease is a function of the MMIC manufacturing yield, since a high yield allows a higher layout density and consequently fewer MMICs per transceiver, and of the improvement in packaging techniques above 60 GHz     

Explicit solution of calibration equations for a dual 6-port network analyser

Application of the 6-port reflectometer for the measurement of complex reflection coefficient, without the direct measurement of phase, is extended to a dual 6-port system for the characterisation of 2-port networks in terms of S-parameters. The system is self-calibrating and no additional standards are needed if the two reflectometers are first calibrated individually by measurements referred to calculated standards of impedance.     

Signal processing aspects of fusion plasma broadband reflectometry

Microwave reflectometry is a radar technique utilized by nuclear fusion diagnostics to evaluate the plasma electron density distribution (density profile) and its local fluctuations in experimental devices, e,g., tokamaks. It exploits the fact that an electromagnetic wave launched into the plasma is reflected at the layer where the refractive index vanishes. By mixing the incident and reflected waves, a phase-modulated reflectometric signal is produced. In O-mode broadband reflectometry, the density profile is determined by sweeping the frequency of the incident wave, estimating the phase-rate of the reflectometric signal and computing its Abel inversion integral. In this paper, a stochastic nonlinear filtering approach is adopted for the estimation problem. The joint phase and phase-rate dynamics is modeled as a vector Gauss-Markov process from which only the first component is observed. A suboptimal nonlinear filter tailored to the features of the problem under study is developed and tested by simulation and applied to real data. This estimator exhibits significant advantages over the extended Kalman-Bucy filter, which is used in this work as a benchmark     

Bottom shape control of optical fiber soot preform by modified VADmethod

Control of the bottom shape of an optical fiber soot preform fabricated by a modified vapor-phase axial deposition (VAD) method is proposed as a way to realize indirect control of the refractive index profile exponent during soot deposition. The technique is based on the close correlation between the profile and the bottom shape. Diameter and refractive index profile fluctuations of the preform with and without control are analyzed. In the case of no control, the fluctuations are larger, and unstable growth of the preform is observed. By controlling the bottom shape, axial fluctuations in the refractive index profile of a transparent preform are reduced to half the magnitude for preforms with no control, and axial diameter fluctuations of the soot and transparent preform are reduced to below ±0.5%. As a result, fibers with a bandwidth of about 1 GHz km at a wavelength of 0.85 μm can be stably fabricated     

The Calibration and Performance of a Microstrip Six-Port Rdlectometer

The calibration and performance of a microstrip six-port reflectometer consisting of only one six-port coupler is discussed. The positions of the centers of the impedance-locating circles are determined from the calibration constants and their frequency behavior is illustrated. The results of measuring some terminations by the reflectometer and two HP network analyzers are compared within the frequency range from 0.5 GHz to 8 GHz. From this comparison tke useful bandwidth of the reflectometer is found to be from 0.5 GHz to 5.5 GHz.     

A millimeter-wave six-port reflectometer based on thesampled-transmission line architecture

This letter presents a proof-of-concept implementation of a millimeter-wave reflectometer for measuring complex reflection coefficients. The reflectometer is based on the six-port architecture and consists of a single section of WR-10 rectangular waveguide and a set of three Schottky power detectors. Design considerations as well as measurements in the 75 to 110 GHz range are described and discussed. Because of its simple architecture, the reflectometer is amenable to scaling for measurements well into the submillimeter-wave region of the spectrum     

A millimeter-wave six-port reflectometer using dielectric waveguide

A six-port reflectometer circuit that is particularly suited to dielectric-type waveguides is described. Its scattering matrix is derived, allowing for flexibility in design. A phase-shifting network is incorporated in the circuit, and it is shown that a quadrature hybrid can be configured for this purpose. The reflectometer was implemented in a dielectric waveguide for W-band (75 GHz-110 GHz) operation, and measurements are presented     

Ultra‐wideband Coexistence with WiBro

Interference effects of ultra‐wideband devices using the frequency band from 3.1 to 10.6 GHz on wireless broadband are evaluated. The ultra‐wideband emission power spectral density that would be necessary to protect a wireless broadband station is considered. Also, an analytic scheme based on a system level simulation of a WiBro system is proposed.     

Frequency fluctuation of spacecraft radio signals in the circumsolar plasma

Frequency fluctuation data of monochromatic radio waves propagating through the circumsolar plasma in 1975–2002 are systematized and analyzed. The radial dependences of the intensity of the frequency fluctuations are obtained for the decimeter radio waves in the circumsolar plasma from the results of radio sounding using the Ulysses and Galileo spacecrafts. It is demonstrated that the radial profile of the rms frequency fluctuations can be approximated by a power-law function whose exponent is determined by the intensity of the plasma inhomogeneities, the velocity of solar wind, the spectral index of the spatial spectrum of the plasma fluctuations, and the outer scale of turbulence. It is also shown that three different frequency fluctuation regimes are found in the solar wind acceleration region and in the inner and outer regions of the stable solar wind.     

CLBO晶体的宽带三倍频模拟分析

为了研究高效的宽带三次谐波转换技术，采用了分步傅里叶变换和四阶Runge-Kutta法对CLBO晶体的宽带三倍频过程进行了数值模拟，分析了单倍单混和单倍双混模式下三倍频转换效率随入射基频光强度、频谱带宽的变化关系，并与KDP晶体的宽带三倍频转换特性进行了对比。在强度为3GW/cm2的40阶超高斯脉冲入射下，得到单倍双混模式下三倍频转换效率达到60%时对应的频谱宽度为650GHz，这与利用KDP晶体在相同条件下获得的频谱宽度相比，提高了近250GHz。研究结果表明，在单倍双混模式下使用CLBO晶体作为频率转换的非线性晶体可以有效地提高宽带三倍频的转换效率。     

长波长PIN／HBT集成光接收机前端噪声分析

文章研究磷化铟(InP)基异质结双极晶体管(HBT)和PIN光电二极管(PIN-PD)单片集成技术,利用器件的小信号等效电路详细计算了长波长PIN/HBT光电子集成电路(OEIC)光接收机前端等效输入噪声电流均方根(RMS)功率谱密度.分析表明:对于高速光电器件,当频率在100 MHz～2 GHz范围内时,基极电流引起的散粒噪声和基极电阻引起的热噪声起主要作用;频率大于5 GHz时,集电极电流引起的散粒噪声和基极电阻引起的热噪声起主要作用.在上述结论的基础上,文章最后讨论了在集成前端设计的过程中减小噪声影响的基本方法.     

A broadband PHEMT MMIC distributed doubler using high-pass drain line topology

A broadband frequency doubler, based on distributed amplifier techniques, has been designed to operate from 11 to 21 GHz. In order to reject the fundamental signal over a broadband frequency range, the conventional low-pass drain line structure was replaced with the high-pass structure. This topology can suppress fundamental signals over broadband without any balanced structure so that the chip size can be more compact. Measured conversion losses of better than 10 dB from 11 to 21 GHz input frequencies are achieved with fundamental signal rejection better than 12 dB. To the best of our knowledge, this is the first demonstration of distributed doubler using the high-pass drain line topology.