一种新的电离层区域重构方法

针对以电离层模型为参考的电离层重构算法对模型依赖性强、计算复杂、适应性不强的问题，提出了一种不依赖于参考模型的电离层区域重构算法，其仅依靠区域内的采样数据对区域电离层分布进行重构.该算法首先根据重构区域覆盖范围内分布的多个垂测站实测的f_cF₂，构造经度因子、纬度因子与f_cF₂关系式，重构出区域内任一点的f_cF₂；然后选取一个垂测站为基准，构造基准站f_cF₂、f_cF₁与重构对应点的f_cF₂扩展因子的关系式，以及重构距离点上任一高度上的等离子体频率与扩展因子、基准站f_cF₁的关系式，通过该扩展因子及关系式即可得到区域内的电子浓度情况.与均匀电离层假设下合成的斜测描迹相比，本文重构方法合成的斜测描迹更接近真实值，且试验表明其进一步提升了电离层重构的精度.     

Scintillation effects on total fade distributions forEarth-satellite links

Scintillation effects on the cumulative fade distributions for Earth-satellite links are considered. Two combination methods for scintillation and attenuation distributions are compared using filtered and unfiltered 11.2 GHz beacon measurements from Austin, TX, on a 5.8° elevation path. A combination method based on the assumption of independent scintillation and attenuation phenomena is proposed. Attenuation and total fade distributions at 19.8 and 29.7 GHz from Kirkkonummi, Finland, on a 12.7° elevation path, are presented for a summer period. The effects of attenuation and scintillation are also calculated using meteorological data from several radiosonde stations. The calculations show that the relative significance of the scintillation is smaller at frequencies from 20 to 50 GHz than at 12 GHz     

Radiowave amplitude scintillation intensity: Olympus satellitemeasurements and empirical model

The authors summarise the results of a 1 year measurement of earth-space radiowave amplitude scintillation using the Olympus satellite 20 GHz beacon signal received at Sparsholt (51.585°N. 1.5033°W), UK at a path elevation of 28.74°. The diurnal and seasonal trends of scintillation intensity are discussed. A generalised semi-empirical model is obtained, which gives excellent fit to the observed cumulative distribution of scintillation intensity     

Low Insertion-Loss, Sharp-Rejection and Compact Microstrip Low-Pass Filters

Complementary split ring resonators are used to design compact, low insertion loss (IL), low pass filter with sharp cut-off. A prototype filter implementing area is 0.23 lambda_gtimes0.09lambda _g, lambda_g being the guided wavelength at 3-dB cut-off frequency (f_c) 1.887GHz. Maximum IL is within 0.5dB up to 1.717GHz and 20-dB stopband extends up to 3.4f_c     

Prediction of tropospheric amplitude scintillation on a satellitelink

Semi-empirical models are presented for annual and worst-month distributions of scintillation fades, enhancements, peak-to-peak amplitude excursions, and intensity. The models utilize the well-known theoretical scaling of scintillation with signal frequency, antenna diameter, and path-elevation angle, and its empirical dependence on the wet term of atmospheric refractivity. Dependence on time percentage is obtained by detailed regression analysis of experimental scintillation data obtained at Sparsholt, UK (51.5850° N, 1.5033° W) over a one-year period using the Olympus satellite 19.7704 GHz beacon viewed at a nominal elevation of 28.74°. Results are compared where possible with the ITU-R and Moulsley-Vilar scintillation models and with Olympus measurements in Germany     

Influence of near-surface soil moisture on regional scale heatfluxes: model results using microwave remote sensing data fromSGP97

During the 1997 Southern Great Plains Hydrology Experiment (SGP97), passive microwave observations using the L-band electronically scanned thinned array radiometer (ESTAR) were used to extend surface soil moisture retrieval algorithms to coarser resolutions and larger regions with more diverse conditions. This near-surface soil moisture product (W) at 800 m pixel resolution together with land use and fractional vegetation cover (f_c) estimated from normalized difference vegetation index (NDVI) was used for computing spatially distributed sensible (H) and latent (LE) heat fluxes over the SGP97 domain (an area ~40×260 km) using a remote sensing model (called the two-source energy Balance-soil moisture, TSEB_SM, model). With regional maps of W and the heat fluxes, spatial correlations were computed to evaluate the influence of W on H and LE. For the whole SGP97 domain and full range in f_c, correlations (R) between W and LE varied from 0.4 to 0.6 (R~0.5 on average), while correlations between W and H varied from -0.3 to -0.7 (R~-0.6 on average). The W-LE and W-H correlations were dramatically higher when variability due to f_c was considered by using NDVI as a surrogate for f_c and computing R between heat fluxes and corresponding W values under similar fractional vegetation cover conditions. The results showed a steady decline in correlation with increasing NDVI or f_c. Typically, |R|≳0.9 for data sorted by NDVI having values ≲0.5 or f_c ≲0.5, while |R|≲0.5 for the data sorted under high canopy cover where NDVI≳0.6 or f_c≳0.7     

CMOS high-frequency switched-capacitor filters fortelecommunication applications

A digitally programmable high-frequency switched-capacitor filter for use in a switched digital video (SDV/VDSL) link is described. The highest available clock frequency in the system is 51.84 MHz (f_s =2f_clock=103.68 MHz for double sampling) while the three desired low-pass corner frequencies (f_c) are 8,12, and 20 MHz. The double-sampling, bilinear, elliptic, fifth-order switched-capacitor filter meets the desired -40-dB attenuation at 1.3 f _c, and -30 dB at 1.25 f_c. For the 12-MHz corner frequency setting, given the 2V_pp differential input, the measured worst case total harmonic distortion is -60 dB, with signal-to-noise ratio of 54 dB. The analog power dissipation is 125 mW from a 5-V power supply. The test results indicate that the clock frequency can be increased to 73 MHz without any ill effects. More measurements verify that an all-digital CMOS implementation, utilizing metal-sandwich capacitors, performs as well as the special-layer analog capacitors implementation, with a small reduction in the absolute corner frequencies. The prototype IC's are fabricated in a 0.35-μm 5-V (0.48 μm drawn) CMOS process     

Bandwidth Potential of Cascode HBT-Based TWAs as a Function of Transistor ${ f} _{max} /{ f} _{ T}$ Ratio

The bandwidth potential of cascode HBT-based broadband amplifiers following the traveling-wave amplifier (TWA) concept is studied. An approximate expression for the gain of the circuit is derived, which is based on the transistor small-signal model and the artificial transmission-line parameters. In this way, a relation between the HBT cutoff frequencies f_T and f_max and the 3-dB cutoff frequency f_c of the amplifier is obtained. This is very useful for assessing the gain-bandwidth potential of a given HBT technology for cascode-based TWAs. Applying these results, we study the potential of two technologies with different f_max / f_T ratios, an InP technology with f_max / f_T of 120 GHz/190 GHz, and a GaAs technology with f_max / f_T of 170 GHz/36 GHz. The higher influence of /max (compared to f_t) on f_c is quantitatively demonstrated. TWAs in both technologies were realized and measured, and good agreement between measurement and theory is obtained.     

A BiCMOS continuous-time filter for video signal processingapplications

A fully integrated BiCMOS continuous-time filter for video signal processing applications is presented. It incorporates an input clamping circuit, a third-order equalizer, a fifth-order elliptic filter with sinx/x correction, and a 75-Ω driver. The architectures of the input and output amplifiers as well as the filter and the equalizer are chosen based on the extensive study of circuit structures and Monte Carlo simulation to meet the linearity requirement for the broadcast-quality video system. The complete chip achieves a low-pass filter response with a 5.5-MHz cutoff frequency (f_cc), 0.3-dB passband ripple, 20-ns group delay variation up to 0.9 f_c, and 43-dB attenuation at 1.45 f_c. With a nominal 2-Vpp signal at the output, measured results show 0.2% differential gain, 0.38° differential phase, and 1.7-mV rms noise demonstrating 10-bit linearity in a 1.5-μm 4-GHz BiCMOS process technology. The filter active area is 8 mm² and it dissipates 350 mW in a single 5-V power supply     

High-repetition-rate optical pulse generation using a rationalharmonic mode-locked fiber laser

Rational harmonic mode locking takes place in an actively mode-locked fiber laser when the modulation frequency f_m=(n+1/p)f_c, where n and p are both integers and f_c is the inverse of the cavity round-trip time, the 22nd order of rational harmonic mode locking has been observed when f_m ≈1 GHz. An optical pulse train with a repetition rate of 40 GHz has been obtained using a modulation frequency f_m=10 GHz. The theory of rational harmonic mode locking has also been developed. The stability of the mode-locked pulses is improved considerably when a semiconductor optical amplifier is incorporated into the fiber laser cavity. The supermode noise in the RF spectrum of a mode-locked laser is removed for a certain range of current in the semiconductor optical amplifier     

Prediction of slant path rain propagation statistics usingdual-polarized radar

The authors conducted a year-long experiment in which a dual-polarized S-band radar probed the volume surrounding two 11.45-GHz satellite downlink paths during rain. Accuracy was assessed by comparison to directly measured link attenuation with two 11-GHz beacon receivers 7.3-km apart at an 18.5° elevation angle, one colocated with the radar. Drop size distributions calculated from the radar horizontal reflectivity (Z_H) and differential reflectivity (ZDR) measurements were used to predict 11.45-GHz satellite beacon attenuations. The radar-predicted attenuations and those measured on the radio links agree, both on an event basis and in terms of annual cumulative distributions     

A CMOS continuous-time Gm-C filter for PRML read channelapplications at 150 Mb/s and beyond

Design techniques for equiripple phase CMOS continuous-time filters are presented, and their integration within a partial-response maximum likelihood (PRML) disk drive read channel is discussed. A programmable seven-pole two asymmetric zero filter implementation is described based on a new transconductance (G_m) cell. The impact of integrator finite output impedance, excess phase, and other implementation related nonidealities is discussed. A filter tuning circuit that requires an accurate time base but no external components is presented. The filter has a cutoff frequency (f_c) range of 6-43 MHz, where f_c is the -3 dB point of the magnitude transfer function with the two zeros set to infinity. Also, with finite zeros it is able to provide up to 12 dB of boost which is defined as the maximum value of the magnitude transfer function referred to dc. The group delay ripple stays within ±2% for frequencies below 1.75 f _c. The cutoff frequency exhibits a 650 ppm/°C temperature dependency and a variation of ±1%/V with the power supply. Total harmonic distortion (THD) values are below -40 dB at twice the nominal operating input voltage (V_nominal=320 mV peak-to-peak differential), and the dynamic range exceeds 60 dB (for a maximum input signal of 640 mV peak-to-peak differential, maximum bandwidth setting, and no boost). Both the filter and a tuning circuit were implemented in a 0.6-μm single-poly triple-metal n-well CMOS process. They consume 90 mW from a single 5 V power supply and occupy an area of 0.8 mm²      

Digital detection of instability of higher order bandpasssigma-delta converters

A digital method of stabilising higher order sigma-delta converters is presented. Results are given for a third order bandpass ΣΔ converter with three continuous time LC filters tuned to 1/4 of clock frequency f_c     

Implementing adaptive power control as a 30/20-GHz fadecountermeasure

Satellite systems in the 30/20-GHz band are very susceptible to outages due to rain-induced fades. In order to reduce the impact of these fades, it has been proposed that the power of a transmitting ground station be adjusted during the fade to compensate for the additional attenuation. Real-time frequency scaling of attenuation from the downlink to the uplink shows promise for estimating the uplink attenuation for uplink power control (ULPC). A scaling-type ULPC algorithm using 20-GHz attenuation scaled to 30 GHz is presented. The limitations of such an algorithm and the effects of scintillation on ULPC are explored. The algorithm is tested using OLYMPUS fade data measured on the 14° elevation OLYMPUS to Blacksburg, VA path. An ULPC scheme employing a beacon at the uplink is also presented. It offers better performance than scaled downlink attenuation ULPC     

Prediction model for the diurnal behavior of the troposphericscintillation variance

Tropospheric scintillation is caused by variations of the refractive index due to turbulence. The only meteorological input parameter for two common current scintillation models by Karasawa et al. (1988) and by the ITU-R is the monthly average of the wet part of the refractivity N_wet at ground level, which is not directly associated with turbulence. The diurnal correlation between N_wet and scintillation variance is very weak. Because clouds and cloud formation are closely associated with the turbulence, quantitative cloud parameters were looked for. Cloud type information based on edited synoptic cloud reports are available from the common database of CDIAC and NCAR. Both diurnal and seasonal variations between scintillation variance and average amount of Cumulus type clouds are well correlated. Using this cloud information together with N_wet, a new method for tropospheric scintillation variance predicting also the diurnal variations is introduced. This model is derived and tested using scintillation measurements at four sites in different climates in Finland, United Kingdom, Japan, and Texas     

Cloud-induced effects on monthly averaged scintillation amplitude along millimeter-wave slant paths

A physical-statistical analysis of cloud-induced effects on millimeter-wave amplitude scintillation along Earth-satellite slant paths is presented. Using numerical simulations derived from a cloud radiative model, a dual-channel nonlinear retrieval algorithm is set up to estimate simultaneously cloud columnar water vapor and liquid water contents from measured ground-based brightness temperatures. The latter are related in cloudy conditions to surface meteorological variables and columnar water vapor and liquid water contents. ITALSAT ground-station data consisting of time series of beacon scintillation at 18.7, 39.6, and 49.5 GHz, surface meteorological data and radiometric observations at 13.0, 23.8, and 31.6 GHz, are used for an experimental analysis of cloud-induced scintillation by selecting a period of six years from 1994 to 1999. The results show a significant correlation between amplitude scintillation variances and cloud columnar contents on a monthly basis (i.e., averaged on-time intervals of one month). Considerations about possible impact of this analysis on the development of scintillation prediction models are finally illustrated.     

Wide Band Metallic Waveguide With In-Line Dielectric Rods

Conventional rectangular metallic waveguides are seldom used at frequencies higher than twice the cutoff frequency because of higher mode propagation. Single-mode propagation is available for a metallic waveguide with arrayed dielectric rods at the center of the waveguide in the frequency under twice the cutoff frequency region using the TE₂₀ mode, and in the frequency over twice the cutoff frequency region using the TE2o mode. If the metallic waveguide and dielectric loss tangent are assumed to be WR-90 (f_c ap6.55 GHz) and 3times10^-4, respectively, then the attenuation constants are smaller than 0.25 dB/m in the frequency range from 7 to 10 GHz, 15 to 16.5 GHz, and from 17.2 to 21 GHz.     

Case study of intense scintillation events on the OTS path

Selected events of enhanced field amplitude fluctuations recorded on the Orbital Test Satellite (OTS) path have been analyzed. The statistical properties of the beacon signals together with their correlation with the concurrent radiometric signal suggest that both scintillation and a variable attenuation mechanism act to produce the field fluctuations. Analysis of the coherence between the beacon and the radiometric signals gives an indication of the fluctuation frequency range over which each effect prevails. The comparison between scintillation data collected by a large (17 m) and a small (3 m) antenna indicates that the turbulence of the refractive index was particularly high during the course of the considered events     

Short term distribution of amplitude scintillation on a satellitelink

The results of an extensive study of the distribution of scintillation amplitudes over short term periods observed during a one year measurement using the Olympus 20 GHz beacon signal are presented. The authors show that scintillation amplitude fluctuation follows a Gaussian distribution during short term intervals of weak-to-moderate fluctuations but departs significantly from this model during strong scintillations or long time periods for which meteorological conditions are not constant     

Traveling-Wave Amplifiers in Transferred Substrate InP-HBT Technology

Promising transistor results of an InP transferred substrate (TS) technology are presented. f_t and f_max are reported as high as 420 and 450 GHz, respectively. Processing has been developed to a full monolithic microwave integrated circuit compatible technology with metal-insulator-metal capacitors, NiCr resistors, and a multilevel wiring scheme. As an example, traveling-wave amplifiers (TWAs) have been designed and realized in a microstrip environment. Simulations of the environment have been done, and are presented in this paper. They have then been used as a design kit to perform circuit simulations. The TWAs demonstrate a gain of 12.8 dB and a 3-dB cutoff frequency f_c of 70 GHz. To the authors' knowledge, this is the highest proven bandwidth of a broadband amplifier in TS technology.