Limitations of Microwave and Millimeter-Wave Mixers Due to Excess Noise

Previous analytical work on microwave and millimeter-wave mixers concentrated on circuit aspects, utilizing for the analysis a simple noise model consisting of shot and thermal noise sources at a constant temperature. However, measurements show that the excess noise created in the diode by hot electrons, intervalley scattering, and traps at the metal-semiconductor interface can be important, especially in millimeter-wave mixers. In this paper, the method of calculation of mixer noise performance in the presence of excess noise is given and its influence discussed for room-temperature, as well as for cooled, mixers.     

Carrier Pulses at Microwave and Millimeter-Wave Frequencies

This paper discusses some recent experimental results obtained using special gallium arsenide point-contact diodes for the generation of phase-locked carrier pulses in the microwave and millimeter-wave bands. Several methods of generating such pulses are described. 11.2-Gc microwave phase-locked carrier pulses of about 1.0-nanosecond base duration have been generated at a 160-megabit/second rate. These microwave pulses, which are generated directly from a baseband signal, normally have peak power levels in excess of 0.5 mw. Millimeter-wave phase-locked carrier pulses have also been generated at 56 Gc. These very high frequency pulses have a base duration as short as 0.25 nanosecond and occur at a 160-megabit/second rate. Furthermore, phase-locked carrier pulses have been generated at frequencies as high as 89.6 Gc. A simple method of generating nonphase-locked 0.3-nanosecond millimeter-wave carrier pulses directly from 1.92 gigabit/second rate baseband pulses has also been investigated. The experimental arrangement used to demonstrate the "turn on" and "turn off" principle of transient carrier pulse generation is described.     

Millimeter-Wave Attenuation Due to Fog and Clouds

The parameters of gamma drop size distribution model of fog and clouds are derived based on the liquid water content and optical visibility, the attenuation are calculated and discussed with this model and empirical relations of the liquid water content and the visibility or other parameters of fog and clouds. A new empirical formula to estimate fog and clouds attenuation is presented based on the Reyleigh absorption approximation, which is more accurate in general and can be used in wider frequency and temperature range than other empirical formulas.     

反射面天线欧姆损耗噪声温度的计算

在超低噪声系统中,天线欧姆损耗噪声也是很重要的。利用金属导体表面的电磁波传播的反射系数,推导出不同极化波的反射面天线金属表面欧姆损耗引起的噪声温度计算公式。以铝合金面板为例,计算了多频段65 m射电天文望远镜天线欧姆损耗的噪声温度。依据计算结果论述了天线欧姆损耗噪声的变化规律。     

On Noise in Distributed Amplifiers at Microwave Frequencies

Formulas for the noise figure, and the minimum noise figure of a multi-link distributed amplifier have been developed. In addition, a relatively simple approximation formula has been devised that predicts the minimum noise figure of a practical amplifier design with good accuracy up to frequencies of 9 GHz. Finally, after the dependence of the noise characteristics on the circuit parameters is discussed, the noise figures of a 2--18-GHz three-link module are computed and compared with those measured on an actual amplifier. The measured data across the 2--18-GHz band compare favorably with the computed results. Measurements and theory agree that only small improvements in noise figure may he achieved, when noise matching the module's input impedance.     

Permittivity Measurements of Lossy Liquids at Millimeter-Wave Frequencies

A measurement system is described which allows the determination of the complex permittivity of high-loss liquids at millimeter waves. Basically, the setup consists of a waveguide interferometer whose unknown arm embodies a liquid holder irradiated by an open-ended rectangular waveguide. The sample thickness is varied by means of a piston driven by a micrometer screw. The bridge output then is read as a function of the liquid thickness. Best fitting between experimental and computed data through a suitable model of the system enables the permittivity to be determined. The system can operate, with high sensitivity, over the whole frequency range of the dominant mode propagating in the waveguide setup employed. System performance is described through a set of experimental results obtained on ethanol, methanol, and pure water at 20° C and 70 GHz.     

Television Broadcasting at Microwave Frequencies

Over 125 Multipoint Distribution Service (MDS) transmitting stations have been constructed over the past seven years. Each of these stations is equivalent to a low power television broadcast station operating on a microwave frequency at approximately 2,150 MHz. The problems encountered in the design and construction of an MDS station differ markedly from a VHF or UHF television station. The propagation characteristics, likewise, are significantly different than for either UHF or VHF frequencies. The solution to the problem of effective coverage and reception throughout a service area requires innovative designs and techniques, and these are described.     

Duplexing Systems at Microwave Frequencies

The paper reviews the various methods of duplexing at microwave frequencies. General principles, including the use of passive and solid-state devices, are first discussed. The characteristics of gaseous-discharge duplexing tubes of both self- and externally-excited types are examined and data for typical examples given. The various arrangements of discharge tube duplexers and methods of measuring their performance are described. The survey concludes with a bibliography.     

微波频段金属接触非线性引起的无源互调功率电平的分析和预测

微波频段由于金属接触非线性引起的无源互调可对系统性能造成严重影响。本文讨论了微波频段金属接触非线性的主要机理和简化模型 ,推导了双正弦输入时任意奇数阶无源互调幅度的多项式表示式和矩阵表示式 ,并给出了三阶和五阶无源互调功率的表示式。作为应用实例 ,利用微波频段金属接触引起的低阶无源互调功率电平的测量值 ,对其高阶无源互调功率电平进行了预测 ,通过比较发现 ,预测结果与测量结果基本一致     

Noise Due to Pulse-to-Pulse Incoherence in Injection-Locked Pulsed Microwave Oscillators

It is demonstrated that partial pulse-to-pulse coherence in a pulsed oscillator system gives rise to no excess noise, which may be significantly reduced by injection Iocking.     

New Measuring Apparatus for Complex Permittivity at Millimeter-Wave Frequencies

A dielectric rod resonator excited by a nonradiative dielectric waveguide is used for measuring complex permittivity of low loss dielectric materials. The complex permittivties of single crystal sapphire, polycrystalline Ba (Mg_1/2 W_1/2) O₃ and Mg₂ Al₄ Si₅ O₁₈ (cordierite) have been obtained at 60 and 77 GHz by the new apparatus. The first time the measurement results of complex permittivity of brain grey and white matters from 15 to 50GHz utilizing a two-port microstrip test fixture is presented. S-parameters of Test fixture are simulated employing the finite-element method. A new spectrometer for the precision measurement of dielectric permittivity and loss tangent, which is capable of providing high resolution data for the first time over an extended W-band (68-118 GHz) frequency for specimens with a large range of absorption values, including highly absorbing specimens that otherwise would not be possible.     

A Dual-Mode Beam Waveguide Resonator and Frequency Stabilizer at Millimeter-Wave Frequencies

By applying perturbation theory to one of the higher modes that may exist in the beam waveguide resonator (also known as the focused Fabry-Perot interferometer), it can be shown that the degeneracy of the mode system can be reduced, resulting in two mode systems with slightly different resonant frequencies. Using this result, a dual-mode frequency discriminator was constructed and used as a reference element for stabilizing the frequency of microwave sources. The stability of a 34-GHz stabilized source was better than 1 part in 5X10/sup 7/ short term and better than 1 Part in 1.5X10/sup 6/ long term. The frequency sensitivity of this dual-mode resonator to changes in the properties of the dielectric medium between the end plates was utilized to determine the dielectric constant of gases at 34 GHz with an accuracy of a few parts in 10/sup 7/.     

Biological Tissues Characterization at Microwave Frequencies

The present work is concerned with the measurement of dielectric permittivity and conductivity of various high loss tissues from freshly sacrificed animals. The measurement makes use of the 'infinite sample' technique which involves mounting of the sample in a rectangular waveguide system excited in the TE/sub10/ mode at 9.4 GHz. A more complex system consisting of skin-fat-muscle combination is also studied. An evacuation of relaxation times is made in all the cases. It is hoped that these data will be relevant in further quantifying the available results in this frequency range.     

Temperature Effects on Attenuation Due to Rain for Millimeter and Centimeter Waves

Radio wave operating in millimetrewave and microwave frequency bands are adversely affected due to rain. Particularly the attenuation is of immense significance for sensitive remote measurements by satellites using frequencies greater than 10 GHz. Maintenance of an uninterrupted communication link requires a precise knowledge of the attenuation effect due to rain for commissioning right kind of transmitting sources for various purposes required in present day situation. Precise measurement of attenuation at various frequencies will enable us to choose the right frequency, polarization, incident angle and power of the source for different purposes. In this paper we have compared the results of earlier works using aR^b Olsen et al, (1) and the formulation by Moupfouma, (2) on the basis of theoretical analysis for explaining the observed results. Effect of temperature, considered in detail in this communication, has contributed the necessary correction factor of the rain attenuation for explaining the observed results. Theoretical analyses to measure the attenuation of the propagating wave due to temperature variation in the rain path have been presented. Correction factor due to temperature profile (temperature from the ground to the rain height within which the radio wave traces its path) has been incorporated in two models by using the concept of dipole energy changes. The effect of this temperature is noted to be quite significant and incorporates an error to the extent of 7–8%.     

遥感微波辐射计逆向辐射噪声对天线温度标定的影响

本文分析了遥感微波辐射计的逆向辐射噪声温度和口面定标源的亮度温度，建立了口面定标源的亮度温度模型。深入分析用口面定标方法反演微波辐射计的天线温度时过向辐射噪声对天线温度标定的影响。     

Frequency Scalable Model for MEMS Capacitive Shunt Switches at Millimeter-Wave Frequencies

This paper presents an approach to RF microelectromechanical systems (MEMS) capacitive shunt switch design from $K$-band up to $W$-band based on the scalability of the RF MEMS switch with frequency. The parameters of the switch's equivalent-circuit model also follow scaling rules. The measurement results of the fabricated switches show an excellent agreement with simulations that allow to validate the MEMS model in the entire band from 20 up to 94 GHz. This model is going to be used in the phase shifter circuit design for antenna array applications. The first 60-GHz phase shifter results are also reported here.      

有源阵列天线的噪声温度

有源阵列天线系统的噪声是有源相控阵雷达系统噪声的主要成分,通过建立基于有源阵列天线系统的噪声分析模型,给出该系统噪声温度的具体计算方法,得到该系统噪声温度的计算公式,进一步推导出该系统增益与噪声温度比值的计算和测试方法.并通过实际计算分析,验证了该方法的有效性.     

Power and Area-Efficient Adaptive Equalization at Microwave Frequencies

We present a low power analog adaptive equalization technique suitable for combating inter-symbol-interference at very high data rates. The proposed technique, which we term the lumped parameter equalizer, addresses several of the problems associated with conventional microwave equalizers based on the tapped delay line structure. The theory is given, and simulation results comparing it with the performance of ideal tapped delay line filters are shown. Circuit implementations are discussed, along with the effect of nonidealities on equalizer performance.