Adaptive antenna system design for multi-element combining with transient interrupted channels

This paper presents an analysis and design procedure for a buoyant cable array antenna used for satellite communications. The towed multi-element array is susceptible to washovers and fluctuations due to the ocean wave interaction with the floating hose where the elements are housed. A model of system performance for coherent multi-element combining is presented based on the dropouts and fades of the individual elements. The array design, including the number and spacing of elements, is shown to be highly dependent on the individual element exposure characteristics and the degree of correlation of the fades between channels. The joint statistics of the array are analyzed using a binary conditional element exposure model and a first-order Markov interelement correlation model. Using this analysis, a family of array designs meeting the communications requirements is produced.     

LiNbO3 optical waveguides formed in a new proton source

Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r₃₃=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided     

Exact pairwise error probability of space-time codes

We describe a simple technique for the numerical calculation, within any desired degree of accuracy, of the pairwise error probability (PEP) of space-time codes over fading channels. This method applies also to the calculation of E[Q(√ξ)] for any nonnegative random variable ξ whose moment-generating function Φ_ξ(s)=E[exp(-sξ)] is known. Its application to the multiple antenna independent Rayleigh-fading channel and to the Rayleigh block fading channel is discussed, and illustrated by two simple examples     

Quantisation noise control in perceptual audio coding using low selectivity filter banks

The problem of computing, in a subband audio coder, the maximum quantisation noise power that can be injected in each band to ensure transparent coding when low selectivity filter banks are used, is addressed. A low complexity strategy, taking into account the frequency responses of the synthesis filter bank, is proposed for achieving an overall distortion due to quantisation noise always below the masking threshold (provided by a psycho-acoustic model) for any length prototype filters.     

The measurement of solar array discharges in a simulated spaceenvironment

A spacecraft in a plasma builds up charge on all the dielectric surfaces and interfaces. Once the net charge exceeds the dielectric breakdown of the material, a discharge occurs. One of the more susceptible pieces of equipment is the antenna/receiver system. The radiated E-field may be strong enough to create an ambiguous signal which may be misinterpreted by the system electronics and cause a system malfunction. A technique is developed to monitor the radiated E-field of materials discharging in an electron environment, using vacuum chambers for measuring the material discharges which are made of highly reflective materials. These chambers affect the radiated E-field due to multiple reflections from the walls. The technique developed defines a method for correcting the effects caused by the measurement facilities. The methodology is: monitor the radiated E-field with a broadband dipole antenna, and digitize the radiated signal as a function of time. Determine the frequency response of the radiated E-field using an FFT algorithm. Measure the transmission and reflection characteristics of the two-port network inside the measurement chamber, and determine the impedance network from the measured E-parameters across the frequency band of interest. Transform the measured E-field frequency response through the impedance network to obtain the frequency response of the actual radiated discharge current. Find the inverse FFT of this response to obtain the actual radiated discharge current response. This technique aids in the prediction of the E-field coupling into receive antennas on-board actual satellites     

Near-field corrections to site attenuation

The theoretical model used for calculating normalized site attenuation for broadband antennas in ANSI C63.4-1992 and for antenna calibration in ANSI C63.5-1988 includes only the radiation terms in the electric field. The omission of the near field terms leads to errors of as much as 2.0 dB at 30 MHz for horizontally polarized antennas separated by 3 m. Corrected values of normalized site attenuation and E _D^max are presented for the 30-300 MHz frequency range     

Crosstalk between microstrip transmission lines

Methods for prediction of crosstalk between microstrip transmission lines are reviewed and simplified for the weak-coupling case. Classical coupled transmission line theory is used for uniform lines, and potential and induced EMF methods are used for crosstalk between nonuniform lines. It is shown that the potential method is equivalent to classical coupled transmission line theory for the case of uniform lines. An experiment was performed for uniform coupled microstrip lines for frequencies from 50 MHz to 5 GHz, and good agreement between theory and measurement was obtained for both near- and far-end crosstalk     

High-frequency analysis of the Ellipticus antenna

Efficient numerical solution techniques have been developed and used to examine the electromagnetic fields that can be developed in the working volume of the CW Ellipticus antenna operated at frequencies from 100 kHz to 1 GHz. An exponentially tapered transition section is designed to obtain the desired illumination pattern in the working volume. The input transition section is needed for impedance matching and to drive efficiently the Ellipticus antenna. A parametric study is performed to ascertain the performance of the Ellipticus antenna for frequencies up to 1 GHz     

Microscopic simulation of electronic noise in semiconductormaterials and devices

We present a microscopic interpretation of electronic noise in semiconductor materials and two-terminal devices. The theory is based on Monte Carlo simulations of the carrier motion self-consistently coupled with a Poisson solver. Current and voltage noise operations are applied and their respective representations discussed. As application we consider the cases of homogeneous materials, resistors, n⁺nn ⁺ structures, and Schottky-barrier diodes. Phenomena associated with coupling between fluctuations in carrier velocity and self-consistent electric field are quantitatively investigated for the first time. At increasing applied fields hot-carrier effects are found to be of relevant importance in all the cases considered here. As a general result, noise spectroscopy is found to be a source of valuable information to investigate and characterize transport properties of semiconductor materials and devices