The Coupled-Cavity Transmission Maser-Analysis

This paper discusses an analysis of a maser amplifier structure (developed at Hughes Research Laboratories) consisting of a cascade of iris-coupled /spl pi/ / 2 cavities intermixed with isolators. Starting from the basic media susceptibility, narrow-band equivalent networks and matrix representations are derived for maser and isolator cavities. A rational function approximation to the over-all gain function is thereby derived by matrix methods. From one viewpoint, the over-all amplifier may be regarded as a negative-resistance inverse-feedback amplifier. The key design parameter is shown to be the isolator roundtrip attenuation. Excess isolation yields an overly rounded gain-frequency characteristic, while deficient isolation yields a characteristic with excess ripple or instability in the extreme cases. The feedback effects associated with intermediate "optimum" values of isolation reduce the effective gain per cavity below the normal gain of a single cavity, but in return one obtains a reduced gain sensitivity which may be reduced to a value comparable to or lower than that of the pure traveling-wave maser.     

Staggered heat sinks with aerodynamic cooling fins

The effect of aerodynamic shaping of the cooling fins in staggered heat sinks is numerically studied. It is shown that by rounding the cooling fins, the aerodynamic efficiency is increased without affecting the thermal efficiency. Three different geometries (in-line rectangular, staggered rectangular and rounded staggered shape) have been compared. These three different layouts were studied to obtain the best ratio between the removed heat and the energy spent to drive the coolant flow through the cooling fins. The main purpose of the paper is to determine the influence of the rounded shape on the average performance. As an example, it was found that a rounded staggered fin layout removes the same heat for an incident air velocity of 4 m/s as a classical in-line fin layout with a higher air speed of 6 m/s, with a reduction of fan power consumption by more than 60%.     

Full-wave analysis of broad wall slot's Characteristics in rectangular waveguides

A rigorous analysis of the resonant characteristics for a broad wall waveguide slot by using the finite-difference time-domain method is presented. Four types of slots including a radiating longitudinal shunt slot, a longitudinal/transverse coupling slot, a centered-inclined coupling slot and a compound coupling slot are analyzed. Lots of slot characteristics such as the resonant length, scattering parameters and normalized admittance in different offsets, tilt angles or slot sizes are obtained. Because the shape of slots is a rectangle with rounded ends in practical fabrication, an accurate modeling and computation for the slots with rounded ends is implemented, and the resonant lengths calculated coincide well with the Stegen's measured data and method of moments results. From these computed results, it is found that all the resonant characteristics of the slots with rounded ends are significantly different from those with normal rectangular ends.     

A novel IEEE rounding algorithm for high-speed floating-point multipliers

Modern floating-point multipliers perform rounding in compliance with the IEEE 754 standard. Since rounding is on the critical path, high-speed rounding algorithms are used to increase the performance for floating-point multiplication. To achieve high performance with minimum increase in hardware, existing rounding algorithms generate two consecutive values in parallel, and compute the rounded product using these values. This paper presents a novel IEEE rounding algorithm which generates two nonconsecutive values in parallel to compute the rounded product. Synthesis results for double precision operands show that the proposed algorithm has approximately 24–41% less delay than previous high-speed rounding algorithms presented elsewhere. The verification of the new algorithm is also presented in a simple and straightforward manner.     

Diffraction by a rounded wedge with an hybrid method MM/PO

The paper deals with an hybrid method, combining a method of moments and physical optics, to compute the diffraction by wedges with arbitrary rounded edges. The vicinity of the rounded part of the wedge is meshed and the current is computed by using the mom. Far from the rounded part, the current is assumed to be equal to the physical optics current. The results of the hybrid method are compared to the results available in the literature for the special case of a wedge with a circular edge.     

Backscatter and attenuation by falling snow and rain at 96, 140,and 225 GHz

The results of measurements are presented for backscatter cross section per unit volume and attenuation for falling snow and rain at 96, 140, and 225 GHz. The attenuation due to rain is almost independent of the measurement frequency, but for snow the attenuation is considerably greater at 225 GHz than at 96 GHz. The rain attenuation generally varies with the rain accumulation rate in accordance with an aR^b relationship for a Laws and Parsons drop-size distribution where R is the rain rate and a and b are constants. The attenuation at all three frequencies is about 3 dB/km for a rain rate of 4 mm/h. The attenuation due to snow varies with airborne snow-mass concentration, with the average rates of increase being 0.9, 2.5, and 8.7 (dB/km)(g/m³) at 96, 140, and 225 GHz, respectively. Generally the attenuation for snow is lower than that for rain. The backscatter cross section per unit volume for rain at 96 GHz is about -35 dB m²/m³ for a rain rate of 4 mm/h. The backscatter from snow at 96 GHz is much lower than that from rain under equivalent accumulation rates or airborne mass concentrations. Snow backscatter at 140 GHz is comparable but higher than that at 96 GHz     

On the Space-Time Variations of Rain Attenuation

Rain attenuation shows a considerable temporal and spatial variability. To simulate fade mitigation techniques such as route diversity, a space-time channel model which accounts for the spatial and temporal variation of rain attenuation is needed. In this paper we investigate the space-time correlation of rain attenuation utilizing 42 GHz star-like network measurements. By combining the spatial and temporal correlation properties of rain attenuation, a simulation model for generating multiple correlated rain attenuation time series based on the Maseng–Bakken model is developed. The model is validated by comparing the statistical and angular diversity properties of the model with those of measurements and theoretical diversity gain models. Furthermore, parameters for the Maseng–Bakken dynamic rain attenuation model were extracted from the star-like network measurements. In addition, using a systematic multivariable technique a model for the parameter $beta _{s}$ which controls the dynamics of rain attenuation in the Maseng–Bakken model was developed. Moreover, using available rain attenuation measurements the advantage of route diversity with selection combining is investigated.      

A simple expression for estimating attenuation by fog at millimeter wavelengths

At millimeter wavelengths, fog attenuation is a function of the fog density, extent, index of refraction of the fog medium, and wavelength. The attenuation is usually determined by first estimating the index of refraction of water for the wavelength and temperature of interest and then calculating the attenuation using the Rayleigh approximation. In this communication fog attenuation is computed for a large set of wavelengths and indices of refraction. A regression analysis of the attenuation is then conducted as a function of wavelength and temperature. It is shown that an almost perfect fit can be obtained with a four-term regression on wavelength and temperature for the ranges of 3 mm <lambda < 3cm and-8degC< T < 25degC, respectively 5666. This expression produces a normalized fog attenuation; the total attenuation is easily computed by multiplying the normalized attenuation by the fog density and extent. If fog density data are not available, a formula for estimating the density from fog visibility is given.     

基于西门子的速度斜坡发生器设计与应用

为解决西门子RGJ斜坡发生器功能块只能在T400或组态有FM458的S7-400中应用的问题。文中提出了一种带圆滑的速度斜坡发生器实现方法,基于西门子仿真软件PLCSIM实现STEP7与WINCC的连接,搭建软件测试仿真平台,完成速度斜坡发生器的设计与仿真。斜坡发生器输出值能保持不变或按设定斜率和圆滑时间跟随输入值以圆滑起步、直线升降、圆滑接近、圆滑拐点的方式接近并达到设定值。     

Attenuation Constant of Lunar Line and T-Septate Lunar Line

The attenuation constant /spl alpha/ of the lunar line and that of the T-septate lunar line were derived from the average power loss W/sub L/ and the average power transfer W/sub T/ in each line, that is the ratio, W/sub L//2W/sub T/. The average power loss and the average power transfer for the lunar line and for the T-septate lunar line were derived from their respective field functions. The theoretical attenuation constant of a typical lunar line is less than 0.7 db/ 100 ft for frequencies greater than 2000 Mc. The theoretical attenuation constant of a typical T-septate line is less than 0.9 db/ 100 f t for frequencies greater than 1000 Mc. Experimental measurements of the attenuation constant of a T-septate lunar line agree with the theoretical value. In the 200 to 2000 Mc frequency band, the lunar line and the T-septate lunar line offer a compact and light package without an appreciable sacrifice in peak power handling capacity or attenuation.     

Frequency Scaling of Rain Attenuation for Satellite Communication Links

One year of copolarized signal data from the OLYMPUS satellite's 12, 20, and 30 GHz beacons were examined for frequency scaling of attenuation. The statistics of the ratios of attenuation in dB for the frequency pairs 30/20, 20/12, and 30/12 GHz computed at each 0.1 s-sample instant were found to be nearly independent of fade depth. It was found that attenuation in dB scales with frequency to the 1.9 power. Also, attenuation ratios computed from the separate statistics of attenuation at each frequency for the same level of occurrence are very close to those found from instantaneous attenuation ratios     

Convergence index filter for vector fields

This paper proposes a unique fitter called an iris filter, which evaluates the degree of convergence of the gradient vectors within its region of support toward a pixel of interest. The degree of convergence is related to the distribution of the directions of the gradient vectors and not to their magnitudes. The convergence index of a gradient vector at a given pixel is defined as the cosine of its orientation with respect to the line connecting the pixel and the pixel of interest. The output of the iris filter is the average of the convergence indices within its region of support and lies within the range [-1,1]. The region of support of the iris filter changes so that the degree of convergence of the gradient vectors in it becomes a maximum, i.e., the size and shape of the region of support at each pixel of interest changes adaptively according to the distribution pattern of the gradient vectors around it. Theoretical analysis using models of a rounded convex region and a semi-cylindrical one is given. These show that rounded convex regions are generally enhanced, even if the contrast to their background is weak and also that elongated objects are suppressed. The filter output is 1/pi at the boundaries of rounded convex regions and semi-cylindrical ones. This value does not depend on the contrast to their background. This indicates that boundaries of rounded or slender objects, with weak contrast to their background, are enhanced by the iris filter and that the absolute value of 1/pi can be used to detect the boundaries of these objects. These theoretical characteristics are confirmed by experiments using X-ray images.     

MOEMS variable optical attenuator with improved dynamic characteristics based on robust design

The design and preliminary data of a novel microoptoelectromechanical systems variable optical attenuator (VOA) driven by a pair of V-beam electrothermal actuators is described. This VOA deploys a face-to-face arranged pair of 45/spl deg/ tilted mirrors in front of two coaxially aligned lensed fibers to form retro-reflection planar light path for attenuation. The initial insertion loss is 0.7 dB at 1550 nm and the maximum dynamic range of attenuation is 50 dB, respectively. The polarization-dependent loss is measured as 0.15 dB at 20-dB attenuation. The dynamic attenuation deviation is less than /spl plusmn/0.36 dB at 20-dB attenuation with respect to 20-G shock of periodical mechanical vibration at 1 K Hz, in which it complies with requirements of the Telcordia GR1221 regulations.     

Spectral attenuation measurement for fluoride glass single-mode fibres by Fourier transform techniques

A new spectral attenuation measurement system using a Fourier transform spectrometer is developed. The Fourier transform spectral attenuation measurement (FT-SAM) system makes the signal acquisition time for a wide wave-length range of 1.0?4.2? much shorter than measurement with a conventional dispersive spectral attenuation measurement system. The spectral attenuation for a fluoride glass single-mode fibre, with a minimum loss of 3±1 dB/km at 2.5?m, is measured with this system.     

Rain attenuation measurements over New Delhi with a microwave radiometer at 11 GHz

Rain attenuation measurements over New Delhi carried out with a microwave radiometer installed at the National Physical Laboratory (NPL), New Delhi and operating on 11 GHz for a period of more than three years are presented. For 0.01 percent of time for the period June 1977-April 1978, the attenuation exceeded for the monsoon period is 14.0 dB whereas for the whole year, it exceeds 10.4 dB. During the winter for the same percentage of time, the attenuation exceeded 1.5 dB, whereas for March-April it exceeds 0.5 dB. For the period May 1978-June 1980, it is observed that for 0.01 percent of time the attenuation for the whole year exceeds 9.0 dB. During the winter for the same percentage of time, the attenuation exceeds 1.4 dB whereas for March-April it exceeds 0.4 dB. A comparison of attenuation over New Delhi and those reported elsewhere are discussed. Yearly and worst month time ratio over New Delhi are given also as the values reported for the European region. Comparison of the attenuation distribution and the rate of surface rainfall measured with a rapid-response rain gauge are also given. The comparison shows that for the monsoon period and for 0.01 percent of time, the attenuation value exceeded for 14 dB corresponds to the surface rainfall rate of 140 mm/h. For the monsoon of 1978, 1979, comparison shows that for 0.1 percent of time, the attenuation value exceeded for 9.0 dB corresponds to the surface rainfall rate of 90 mm/h. Variation of attenuation and effective path length for various rainfall rates and elevation angles are also given.     

Millimeter-wave measurements of foliage attenuation and ground reflectivity of tree stands at nadir incidence

In this paper, the phenomenology of wave propagation through foliage and forest ground reflectivity is investigated for assessing the feasibility of foliage-covered target detection at millimeter-wave frequencies. An experimental procedure for simultaneous measurements of foliage attenuation and ground reflectivity is outlined. This measurement procedure is implemented for two different tree stands, one mostly coniferous and the other deciduous, using a nadir-looking, high-resolution, 35-GHz radar positioned above the tree canopy. Statistics of the two-way attenuation and ground reflectivity for these two well-characterized stands are derived. Strong spatial and angular fluctuations in the two-way foliage attenuation coefficient are observed. The mean, standard deviation, and median of the measured two-way attenuation factor at Stand 1 (mostly coniferous trees with 0.140 trees/m/sup 2/ stocking density and 45.45 Kg/m/sup 2/ green biomass) are -25.4, -18.3, and -48.2 dB, respectively, while the mean, standard deviation, and median of the measured two-way attenuation factor at Stand 2 (deciduous trees with 0.1055 trees/m/sup 2/ stocking density and 30.90 Kg/m/sup 2/ green biomass) are -15.4, -12.7, and -33.6 dB, respectively. The mean attenuation rates of Stand 1 and Stand 2, derived from the measured two-way attenuation factor, are 0.40 and 0.24 Np/m, respectively. Only a small percentage of the data had two-way foliage attenuation values exceeding 70 dB. The mean, standard deviation, and median of the power reflectivity of the forest floor at Stand 1 are -14.2, -11.0, and -21.1 dB, respectively, while for Stand 2, the same statistical measures are -16.0, -14.3, and -22.2 dB, respectively. The results demonstrate the potential for using MMW nadir-looking radars for the detection of targets underneath foliage-cover.     

The Study of Rain Specific Attenuation for the Prediction of Satellite Propagation in Malaysia

Specific attenuation is the fundamental quantity in the calculation of rain attenuation for terrestrial path and slant paths representing as rain attenuation per unit distance (dB/km). Specific attenuation is an important element in developing the predicted rain attenuation model. This paper deals with the empirical determination of the power law coefficients which allow calculating the specific attenuation in dB/km from the knowledge of the rain rate in mm/h. The main purpose of the paper is to obtain the coefficients of k and α of power law relationship between specific attenuation. Three years (from 1st January 2006 until 31st December 2008) rain gauge and beacon data taken from USM, Nibong Tebal have been used to do the empirical procedure analysis of rain specific attenuation. The data presented are semi-empirical in nature. A year-to-year variation of the coefficients has been indicated and the empirical measured data was compared with ITU-R provided regression coefficient. The result indicated that the USM empirical measured data was significantly vary from ITU-R predicted value. Hence, ITU-R recommendation for regression coefficients of rain specific attenuation is not suitable for predicting rain attenuation at Malaysia.     

A 0.13-/spl mu/m CMOS 5-Gb/s 10-m 28AWG cable transceiver with no-feedback-loop continuous-time post-equalizer

The frequency-dependent attenuation of the transmission lines between chips and printed circuit boards, for example, is an obstacle to improving the performance of a system enhanced with LSI technology scaling. This is because large frequency-dependent attenuation results in poor eye-opening performance and a high bit-error rate in data transmission. This paper presents a 5-Gb/s 10-m 28AWG cable transceiver fabricated by using 0.13-/spl mu/m CMOS technology. In this transceiver, a continuous-time post-equalizer, with recently developed no-feedback-loop high-speed analog amplifiers, can handle up to 9dB of frequency-dependent attenuation in cables and also achieve an 18-dB improvement in the attenuation (27dB total improvement) by using pre- and post-equalization techniques in combination.     

Diffraction by a wide double wedge with rounded edges

The multiple diffraction by two conducting wedges with rounded edges is investigated, using an expression for the scattered field of a plane wave incident on a single wedge with rounded edge derived by Ross and Hamid, as well as the technique proposed by Karp and Keller for the diffraction by a slit in an infinite screen. Numerical results for the diffraction pattern, transmission coefficient and the effect of rounding are also presented. It is shown that small rounding of the two edges decreases the transmission coefficient for large separation distances between the wedges.     

Atmospheric emission measurements of attenuation by microwaveradiometer at 19.4 GHz

Attenuation measurements on an Earth space path are presented using a passive microwave radiometer operating at 19.4 GHz in the emission mode. Attenuation measured under clear weather showed variation between 0.2 to 1.1 dB, whereas for cloud conditions attenuation as high as 1.0 dB have been recorded. Attenuation measurements for rain events have been correlated with rainfall rate using a fast-response 10 seconds opto-electronic rain gauge. The values of attenuation versus rainfall rate varied between A (dB)=0.01+0.18 R(mm/h) at the minimum and A (dB)=0.01+0.25 R(mm/h) at the maximum, showing considerable variability in the values of attenuation from year to year. The attenuation statistics for different seasons have also been computed and they show considerable changes from season to season-the largest attenuation in excess of 10 dB recorded in July-August-September, whereas minimum attenuation in excess of 2 dB recorded in December-March for nearly two years of data. Comparison of measurements made over New Delhi with those reported elsewhere show that for 0.02% of time attenuation values lie between those of Slough, England, and Crawford Hill, NJ. The concept of effective path length has been discussed based on the relationship between effective path length and the rain rate