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.     

Tele-education at the Open University

Although the lack of non-verbal cues exacerbated everyday teaching problems, tele-teaching was a viable alternative to no personal contact at all.     

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.      

Low-voltage operation of the retarding-field oscillator at X band and in the millimeter wavelength region

This paper concerns the partial development of two low-voltage designs of the retarding-field oscillator. These designs differ fundamentally in their power coupling system. TheX-band model has coaxial-line coupling to a waveguide while the millimeter wavelength model has double-cavity coupling to a waveguide. The design developed atXband allows operation with the anode voltage as low as 200 volts and as high as 600 volts. Radio-frequency output power of 20 milliwatts at 200 volts and better than 1 watt at 600 volts is possible. In the millimeter wavelength range, three double-cavity designs have been investigated. These tubes operate in the range of from 4.30 to 5.20 mm, 5.00 to 6.4 mm, and 5.80 to 6.8 mm, respectively. All of these oscillators have anode potentials of 800 volts or less. An output power of 175 milliwatts has been obtained at a wavelength of 6.00 mm. A digest of characteristics possessed by important models of the retarding-field oscillator investigated as of November, 1957, also is included.     

Recent developments in digital image processing at the image processing laboratory at the jet propulsion laboratory

Image processing of spacecraft images has been carried on at the Jet Propulsion Laboratory since 1964. The most recent advances in removal of geometric distortion and residual image effects along with various types of mapping projections are covered. The recent applications of image processing to the areas of bio-medicine, forensic sciences, and astronomy are discussed. These treatments are of a tutorial nature and should serve as a guide to more complete discussions on the subjects.     

Complex Permittivity of GaAs and CdTe at Microwave Frequencies

The microwave dielectric constant and loss tangent of Cr-doped semi-insulatiug GaAs have been measured in the frequency range 2.5-36.0 GHz and the temperature range 300-400 K. The room temperature dielectric constant is 12.95 and the temperature coefficient alpha ( /spl equiv/ epsilon(0)/sup -1/ d epsilon/dT) is 1.6 x 10/sup -4/ /K. The dielectric constant and loss tangent of CdTe have been measured as functions of temperature at 15.95 GHz. The room temperature dielectric constant is 10.39 /spl plusmn/ 0.04 and the temperature coefficient alpha is 2.5 x 10/sup -4/ /K.     

The Measurement of Phase at UHF and Microwave Frequencies

A theoretical analysis and a unifying classification of methods of measuring phase at UHF and microwave frequencies are presented. The coherent phase bridge circuits are analyzed in terms of the type of modulation applied to the channels of the bridge and the type of combiner and mixer employed at the output of the bridge. In this analysis and classification, identifying characteristics, and some of the relative advantages and disadvantages of these circuits become obvious.     

Microwave emission and reflection from the wind-roughened seasurface at 6.7 and 18.6 GHz

Microwave radiometric observations were made with specially designed microwave radiometers at 6.7 and 18.6 GHz, and the results were compared with those of other investigators, over the frequency range of 1-40 GHz. Dependences of sea surface emission and reflection on wind speed, frequency, incidence angle, and polarization type are discussed in detail, following discussions of the reflective processes of sky radiation and error estimation in the retrieval of mainlobe-averaged brightness temperature. The wind speed sensitivity of brightness temperature, emissivity, and reflectivity is formulated with respect to frequency and incidence angle in each polarization. The brightness temperature, emissivity and reflectivity at arbitrary wind speed are derived employing this formulation. Based on the results obtained it is suggested that the 10-19-GHz band may be optimal for satellite microwave radiometer observations of sea-surface wind     

Microwave propagation through the melting layer at grazing anglesof incidence

A propagation model of the snow-melting layer has been proposed and analyzed. The model is based on two key postulates, namely, that the melting layer has an effective (complex) permittivity which is higher than that of rain or dry snow and that the layer could be inclined by small angles (1°-2°) under certain climatic conditions. The model is successfully used to explain certain anomalous phenomena recently observed on a slant microwave path in the 4-8 GHz range. A further and particularly useful application of the model would be for the analysis of low elevation angle paths to satellites, such as might occur in wet northerly latitudes, e.g. coastal Alaska, eastern Labrador, or coastal Norway     

电路设计中对时钟晶体振荡器的考虑

当在一个抖动敏感电路中使用时钟振荡器时,有一些因素系统设计者必须考虑     

Microwave systems-then and now-examples at the 50th reunion of theMIT Radiation Laboratory

A brief history of the MIT Radiation Laboratory established by the National Defense Research Committee (NDRC) is presented. The focus is on Radlab Projects 2, a gunlaying system including a radar for target acquisition and tracking, a computer to establish tracks and to make fire-control predictions, and the guns and the shells with their fuses, and Project 3, a navigation system. The current situation is discussed, including the impact of advances in technology, both in the microwave field and in complementary fields essential to the design of modern microwave systems. Three examples are briefly reviewed: the Army Patriot, the Navy Aegis, and the AF Navstar of GPS navigation system     

Microwave radiometric imaging at 3 GHz for the exploration ofbreast tumors

A process of microwave radiometric imaging at 3 GHz permits the mapping of radiometric intensities on a square area about half a decimeter on a side. These data, translated in terms of a colored image, point out the existence of lateral temperature gradients in tissues. This system was initially used for examining large breast tumors; at present, it is also used for detecting smaller, impalpable tumors. The rules for characterizing benignancy or malignancy of small tumors which appear in a mammographic examination (X-rays) are defined. The definition of an appropriate parameter, deduced from this image processing, makes it possible to indicate benignancy or malignancy. In experiments conducted on 18 patients, all the malignant lesions had a radiometric ratio greater than 65%, while benign lesions were below 55%. However, a zone of uncertainty (between 55% and 70%) exists where it is wise not to assert malignancy or benignancy     

The regenerative receiver and the synchronous oscillator

The regenerative receiver [1] and the synchronous oscillator (SO) [2]-[4] have one common functional property, that is, their sensitivity is inversely proportional to the input signal level While the regenerative receiver operates in a threshold condition where noise is high, the stability and the selectivity are poor, the SO functions when stable oscillations are maintained and selectivity is good and the noise is low. Although the regenerative receiver is an AM-to-AM converter, the SO is an AM-to-PM converter.     

The Generation and Propagation of Acoustic Surface Waves at Microwave Frequencies

The generation and propagation of acoustic surface waves is reviewed with particular emphasis on the microwave-frequency range. Theoretical work on optimizing the generation efficiency and the bandwidth of interdigital transducers is compared with recent experimental results. The minimum Iinewidth of 0.9 /spl mu/m which can be produced by optical photolithographic techniques places an upper limit of about 1 GHz on the maximum frequency that can be generated at the fundamental mode. Overtone operation has been used to generate 3 GHz surface waves on LiNbO/sub 3/ but this method has the disadvantage of reduced efficiency plus the complication of volume-wave generation. A better solution for generation above 1 GHz is the fabrication of interdigital transducers by means of electron beam exposure of the photoresist. The surface-wave propagation loss gives a significant contribution to the total insertion loss of delay lines operating at microwave frequencies. Losses of 1.1 dB//spl mu/s and 3.8 dB//spl mu/s at 0.9 GHz and 2 GHz, respectively, have been measured for propagation along the Z-direction of Y-cut LiNbO/sub 3/ by means of a laser deflection method. Larger losses have been observed for quartz. The additional complexities for surface-wave propagation due to the anisotropic single-crystal substrates which are necessary at microwave frequencies are also described.     

Dielectric Constant Ferrites and Loss Tangent of Microwave at Elevated Temperatures

Experimental data are given on the effect of elevated temperature on the dielectric properties of ferrites intended for microwave applications. Measurements were made at X band. The real part of the dielectric constant generally increases slowly with temperature, the maximum temperature coefficient observed being 300 parts per million per degree C. The dielectric loss tangent also generally increases with temperature. Measurements were made in a rectangular waveguide cavity, using a modified perturbation technique. It is shown that the simple perturbation technique may cause an appreciable error in the measurement of the real part of the dielectric constant. The effect of the finite resistivity of the cavity walls and the effect of the cavity irises on the measurement of the dielectric loss tangent, are also considered.     

1616MHz微波介质滤波器的设计及制作

提出了一种利用Ansoft-HFSS软件辅助设计微波介质带通滤波器的设计方法。通过公式初步计算出器件结构参数,再利用软件建立器件模型,仿真优化,最终提取准确的结构参数,并采用传统的电子陶瓷生产工艺制备样品。结果表明,样品的中心频率为1 616.7 MHz,3 dB带宽为23 MHz,插入损耗为1.48 dB,电压驻波比小于1.23,带内纹波小于0.1 dB。测试结果与仿真结果相吻合,验证了该设计方法的可行性和正确性。     

Spherical near-field scanning at the Technical University ofDenmark

The early work (1969-79) on spherical near-field antenna measurements at the Technical University of Denmark (TUD) is outlined. A spherical near-field transmission formula is described and the first probe-corrected spherical near-field measurements are discussed. The TUD-ESA (European Space Agency) joint effort on spherical near-field testing is also described     

Research in computational electromagnetics at the University ofMichigan

The history of the Radiation Laboratory at the University of Michigan is briefly recounted, and its present composition of staff, faculty, and graduate students is described. Research in electromagnetic scattering at the laboratory is reviewed, covering high-frequency scattering and two- and three-dimensional numerical simulation. Work on passive monolithic circuits and antennas, including numerical modeling of planar discontinuities and antennas, planar discontinuities and transitions, and antenna feeding networks, is discussed