The Measurement of Noise in Microwave Transmitters (Comments)

The recent comment by Ashley et al. as a reply to the remarks by Knöchel et al. drew my attention to the, work by Ashley Barley, and Rast, Jr., to which I would like to add three supplements. On an improved version of the frequency discriminator of Ondria and Ashley et al., the following results have been published.     

Comments on "The Measurement of Noise in Microwave Transmitters" (Letters)

In the recent paper, "The Measurement of Noise in Microwave Transmitters," J. R. Ashley et al. give a review of several methods for the measurement of AM and FM noise, respectively. The section, which deals with FM noise measurements at frequencies below 5 GHz, may be the source of erroneous conclusions, as will be pointed out in this comment.     

微波器件噪声参数的测量方法

作为微波低噪声器件研制和应用的一项关键技术,噪声参数的测量工作引起行业的广泛关注。论述了噪声参数测量原理,研究了测量系统校准方法,分析了噪声源的反射系数、噪声温度,阻抗调配器的反射系数、S参数、增益,接收机的反射系数、噪声功率等20余项物理量对噪声参数测量的影响,对比了直接冷源法和简化冷源法在接收机传输增益测量中的优缺点,提出了改进型冷源法。最后给出了噪声参数测量不确定度主要影响量的归类分析,为下一步开展噪声参数不确定度评定工作奠定了基础。     

Microwave Noise Characterization of GaAs MESFET's: Evaluation by On-Wafer Low-Frequency Output Noise Current Measurement

A simplified noise equivalent circuit is presented for submicron-gate-length MESFET's in the common-source configuration, consisting of five linear circuit elements: the gate-to source capacitance C/sub gs/, the total input resistance R/sub T/, the transconductance g/sub m/, the output resistance R/sub 0/, and a noise current source of spectral density S/sub io/ at the output port. All of these elements can be determined by on-wafer measurements, and the noise current can be measured at a low frequency. The minimum noise figure of the device calculated from this model, as well as the bias and frequency dependence of the noise figure, is shown to be in agreement with microwave noise figure measurements. Thus a technique has been established for determination of the minimum noise figure of a device solely by on-wafer measurements rather than by the usual microwave measurements. The proposed technique can be employed rapidly, conveniently, without the need for tuning, and at the wafer stage of device fabrication.     

Noise in Microwave Transistors

Details of noise measurement techniques in the L- and S-bands are discussed. The complete noise parameters of microwave transistors are presented in the frequency range 0.6 to 4.2 GHz. Noise figure, available power gain, and noise measure are shown as a function of the source admittance and of the source reflection coefficient. The equivalent circuit and the noise figure of a microwave transistor are evaluated using an analog model.     

微波回传系统发射机数字预失真线性化

微波回传系统是宽带无线通信基站信号回传的主要手段之一.对19GHz微波回传系统发射机的非线性特性进行了实验测试与分析研究,采用基于查找表(LUT)的数字预失真技术对其进行线性化以满足大容量无线基站信号传输的需求.利用指数加权移动平均算法(EWMA)提取发射机的静态非线性特性以构建数字预失真查找表.使用3载波WCDMA信号进行实验验证,实验结果表明采用查找表数字预失真器对该被测发射机进行线性化,3阶互调失真(IMD3)最大可以改善23dB.因此通过简单的查找表数字预失真技术可以有效地提高微波回传系统发射机的线性度,同时可以使微波功率放大器工作在较高的输出功率,增大回传距离,降低生产成本.     

On the Measurement of Noise Parameters of Microwave Two-Ports (Short Paper)

A novel procedure for determining the noise parameters of microwave two-ports is introduced. In this procedure, the computations necessary to find the noise parameters from the set of measurements of noise temperature (noise figure) are greatly simplified. The assessment of accuracy with which the noise parameters can he determined from a given set of measurement data is straightforward.     

遥测发射机中的微波锁相调频技术研究

本文介绍了再入遥测系统中发射机的微波锁相调频技术,分析了几种微波锁相调频方案构成及其电路的性能和应用。研究结果表明,两点注入式微波锁相调频适用于高码速率、宽频带与调制响应要求比较高的遥测系统。     

The Precision Measurement of Noise Temperature of Mismatched Noise Generators

By refining the technique and analysis of an earlier paper, it is shown that a compensation method is the basis of the most precise measurement of noise temperature, especially for cryogenic noise generators. The measurement system is adjusted so that it is in thermal equilibrium with the generator under test. As is typical for the compensation method, the generator under test may be mismatched, and the comparison errors and detector limitations can be verified experimentally. For generators with small reflection coefficients (|/spl Gamma/|is相似文献   

Microwave Thermal Noise Standards

Calibrated microwave thermal noise standards usually consist of a matched resistive element thermally isolated by a transmission line. They are used for microwave radiometry, antenna temperature calibrations, loss measurements, low-noise amplifier performance evaluation, and low-level CW signal level calibrations. The formula used to account for the distributed loss and temperature along the transmission line is derived and simplifying approximations and limitations are noted. Exact (hf/kT<<1) and approximate (hf/kT<<1, /spl pound/<<1) solutions for various loss and temperature distributions are tabulated. A FORTRAN computer program is available for a general solution that uses the transmission-line temperature and loss distributions for input data. The single largest source of calibration error is usually the microwave insertion loss measurements. The construction, calibration, and errors are discussed for a field-operational liquid-nitrogen-cooled waveguide noise standard. This standard is precisely calibrated and has a nominal noise temperature of (78.09 /spl plusmn/ 0.12 peak)/spl deg/K.     

Excess Noise in Microwave Detector Diodes

The dependence of available excess noise in type microwave crystal-diode rectifiers on applied microwave power was measured. This may be approximated by a power law with stants characteristic of the particular crystal. As a consequence of the dependence of both excess noise and dc rectified power on power level, there is a level which minimizes the ratio of these tities. Similarly, in the case of a modulated microwave carrier there is an input level which minimizes the ratio of excess noise to power, and so provides optimum detection of small modulation.     

A Method for Measurement of Losses in the Noise-Matching Microwave Network While Measuring Transistor Noise Parameters

A new method for measuring the loss of a tuner network used as the noise-source admittance transformer in a noise parameter test set is presented. Since the method is based on noise figure measurements, the tuner losses are determined on-line while performing measurements for determining transistor noise parameters. Experiments carried out on a coaxial slide-screw tuner by means of a computer-assisted measurement setup are reported.     

The Simultaneous Measurement of Gain and Noise Using Only Noise Generators

The gain and noise of a linear two-port device can be measured simultaneously using two noise generators as the only signal sources. While this method is usable for measuring all linear two-port devices except those with high loss, it is particularly convenient for low-gain devices, for which it replaces three conventional measurements. The terms "minimum output temperature" and "standard output temperature" are introduced.     

A Method for the Accurate Measurement of the Noise Temperature Ratio of Microwave Mixer Crystals

For the precise measurement of noise temperature ratio of a microwave mixer crystal it is common practice to employ a Roberts coupling network in order to make the Y factor independent of crystal conductance. It is shown here that a number of errors are introduced in this method, the chief of which is failure to consider the effect of transit time loading. It is also shown that the use of cathode lead inductance leads to a much improved measurement of noise temperature ratio.     

A Low-Temperature Microwave Noise Standard

An X-band thermal noise source is described that consists of a waveguide termination, cooled in a cryogenic environment, along with temperature and pressure monitors and controls. With liquid helium as the cryogen, the effective noise output at the room temperature flange can be set to values around the boiling point of helium (4.2/spl deg/K) with an accuracy of /spl plus mn/ O.O5/spl deg/K. With liquid nitrogen as the cryogen, the output temperature can be set to values around 77/spl deg/K with an accuracy of /spl plus mn/ 0.13/spl deg/K. This accuracy is made possible by several unique features. First, the terminating waveguide section is a vapor bulb thermometer with the absorbing load surrounded with the cryogenic liquid. Second, heat exchangers are used to permit an unusually short waveguide transition seetion between cryogenic and room temperature. Third, an absolute pressure regulator is used to control the cryogen boil-off rate resulting in a temperature stability of 0.003/spl deg/K for helium and 0.02/spl deg/K for nitrogen. At present, the useful accuracy of the standard is limited to /spl plus mn/0.1/spl deg/K because of uncertainties in the insertion loss (about 0.001 dB) of mating room temperature flanges.     

微波低噪声SiGe HBT的研制

利用3μm工艺条件制得SiGeHBT(HeterojunctionBipolarTransistor),器件的特征频率达到8GHz.600MHz工作频率下的最小噪声系数为1.04dB,相关功率增益为12.6dB,1GHz工作频率下的最小噪声系数为1.9dB,相关功率增益为9dB,器件在微波无线通信领域具有很大的应用前景     

微波低噪声SiGe HBT的研制

利用3μm工艺条件制得SiGe HBT(Heterojunction Bipolar Transistor),器件的特征频率达到8GHz.600MHz工作频率下的最小噪声系数为1.04dB,相关功率增益为12.6dB,1GHz工作频率下的最小噪声系数为1.9dB,相关功率增益为9dB,器件在微波无线通信领域具有很大的应用前景.     

An Ultra-Low Noise Microwave Synthesizer

A silicon bipolar transistor together with a barium titanate dielectric resonator were used to design a low noise microwave synthesizer. The oscillator was phase locked to a low-frequency (LF) reference with microwave frequency selection provided by a high-speed digital programmable divider within the phase-locked loop. The resulting FM noise Delta f/sub rms/ was 0.0003 Hz in a 1-Hz band greater than 1000 Hz from the 1-GHz carrier.     

微波低噪声放大器机助噪声分析的一种方法

本文提出了微波网络计算机辅助噪声分析的一种方法,推导了所需的等效噪声参数变换公式,这些公式考虑了所有电路元件引入的噪声源.该法可用来解决具有反馈、有耗匹配微波低噪声放大器的噪声分析问题.文中给出了较为详细的噪声分析程序框图.     

金属桁架式透波天线罩的噪声温度

分析了充气式及多层电介质式透波天线罩的优缺点。阐述了在测控系统及射电观察系 统中采用新一代金属桁架式透波天线罩的必然性及其所具有的无线电技术特性稳定、频带宽、可靠性高 和使用方便等一系列优点。按照透波天线罩安装时天线的直接变化而试验性地评估了天线罩对天线噪 声温度的影响，给出了测量金属桁架式透波天线罩对天线噪声温度影响程度的过程、原理、方法和结果。