Showing papers on "Wideband published in 1988"

Aperture-coupled patch antennas with wide-bandwidth and dual-polarization capabilities

Abstract: The authors discuss the design of a wideband, dual-proportion, C-band patch radiator with a 20% bandwidth for input voltage-standing-wave ratio >

Wideband video system for single power line communications

Abstract: A wideband video system transmits and receives video signals through a ground line of a power distribution network. This single line transmission path is not susceptable to noise signals as is a dual line transmission path. The single line transmission path is grounded in the transmitter by a cable from an incoming source and also grounded in the receivers by respective monitors. Between the incoming source and the monitors, a single communication line carries single ended wide band video signals respecting floating grounds through the transmitter, the ground line and the receivers. This single line transmission is less susceptible to noise on the power lines thereby enabling the transmission of up to 500 mHz signals suitable for video transmission over a wide frequency band.

The application of digital signal processing to transmitter linearisation

Abstract: A description is given of three prototype transmitters, using digital signal processing in different ways to achieve linear RF amplification. The Cartesian feedback technique, the adaptive predistortion technique, and the LINC (linear amplification with nonlinear components) technique, are all shown to provide a good degree of intermodulation product suppression (>50 dB), with the LINC amplifier approach potentially the most power-efficient (>70%). Both the LINC and predistortion systems can operate in a wideband mode. The Cartesian approach, because of the inherent feedback control system, is limited to a bandwidth of about 10% of the operating frequency. The implementation costs are considerably reduced over conventional analog realizations of such systems for all three techniques. >

Wideband ambiguity function of broadband signals

Abstract: Broadband signal analysis and design for radar and sonar systems require the use of a wideband ambiguity function (WAF) to estimate their performance. The properties of WAF for FM signals are studied and the results of numerical computation are compared with the theoretical expressions. The main findings presented here include the following. (a) A broadband LFM signal is not a Doppler tolerant one. At high velocity, the magnitude of WAF is similar to the signal envelope, and its range resolution decreases obviously. (b) an LPM signal exhibits a fairly good range resolution, even at very high velocity. The performances of Doppler tolerant signals for three models are described and compared. The different envelopes for the LPM case have little influence on the behavior of WAF. (c) The unbiased delay estimation for both LFM and LPM signals, with bandwidth B= f max− f min and duration T, can be obtained by a special shift in time, which is such that t ∈ ( f minT/B, f maxT/B). An approximate method for derivation of WAF, based on the Doppler cross‐power spectrum and the stationary phase principle, is proposed. Such an analysis is applied to a bat’s sonar signal.

Wideband, aperture-coupled microstrip antenna

Abstract: A wideband, aperture-coupled microstrip antenna comprising a multilayer structure and including a feed layer, a ground plane including an aperture therethrough, a plurality of tuning layers formed of dielectric material, at least one of the tuning layers including therein a tuning element in the form of an electrically-conductive material, herein called a tuning patch, and final radiating layer including a radiating patch The multiple tuning layers serve to extend the operational bandwidth of the antenna as compared to other microstrip antennas Aperture coupling allows realization of the antenna using integrated circuit fabication techniques without the shortcoming of direct physical connections between the feedline and the radiator, and thus providing simple, yet reliable coupling between the feedline and the antenna

A 50-Mbit/s CMOS monolithic optical receiver

Abstract: A general-purpose CMOS optical receiver that operates at data rates from 1 to 50 Mb/s has been fabricated in a 1.75- mu m CMOS process. The technology choice resulted in a high level of integration compared with similar bipolar technology receivers. The measured minimum signal current for a 10/sup -9/ bit error rate at 50 Mb/s is 48-nA r.m.s. Automatic gain control gives the receiver an electrical input dynamic range of greater than 60 dB. The outputs are TTL (transistor-transistor logic)-compatible and the chip dissipates less than 500 mW when switching at maximum speed. The die area is 16 mm/sup 2/. A comprehensive noise analysis of the receiver front end provides insight into the design tradeoffs of optical receiver preamplifiers. A wideband precision amplifier used in the linear channel is discussed in detail. A simple method for recovering low-frequency signal information lost in AC coupling is described. >

Generation of wideband linear frequency modulation signals

Abstract: A low-frequency low bandwidth Linear Frequency Modulation (LFM) waveform, nominally a 1 MHz to 10 Mz swept frequency analog sinusoid or digital square wave, is produced by direct digital synthesis. This waveform is upconverted in frequency and expanded in bandwidth, nominally to microwave frequencies with bandwidths of nominally 160-360 MHz, in a multiplying offset phase locked loop. The phase locked loop also linearly frequency modulates a X-band carrier with the microwave frequency LFM waveform to produce an output signal suitable for Synthetic Aperture Radar. The phase locked loop induces low phase error, and may be closed around the radar transmitter to remove phase errors induced by that unit.

On the design of sharp cutoff wide-band FIR filters with reduced arithmetic complexity

Abstract: The authors provide an approximate analytical characterization for wideband low-pass filters using the frequency masking approach introduced by Y.C. Lim (ibid., vol.CAS-33, no.4, p.357-64, Apr. 1968). They extend this realization to the case of wideband bandpass filters. Approximate expressions of the optimal value of the interpolating factor L are derived that minimize the total arithmetic hardware used in the overall realization. Expressions for the number of adders and multipliers required are also derived. The proposed two-branch realization is computationally more efficient than that conventional direct-form realization, with a moderate increase in the number of delays. The noise performance of these wideband designs compares very favorably with those of equivalent direct-form realizations. >

Microwave-multiplexed wideband lightwave systems using optical amplifiers for subscriber distribution

Abstract: A lightwave systems analysis shows that microwave-multiplexed wideband services can be distributed to large numbers of subscribers by using optically amplified multiple-star lightwave distribution networks. Through the use of well developed, readily available microwave electronics, this technique enables lightwave systems to take advantage of the large available bandwidth of single-mode fibres, GaInAsP lasers and GaInAs photodetectors.

New inline wideband dynamic semiconductor laser amplifier model

Abstract: The formulation of a new scattering matrix, and the use of a gain compensation term allows the transmission-line laser model, previously described, to simulate both travelling-wave and Fabry-Perot laser amplifiers. The new model's results are in excellent agreement with those of other workers for both static operation of travelling-wave amplifiers and dynamic switching of Fabry-Perot amplifiers. To show the wideband nature of the model, a single-repeater 2 Gbit/s fibre communication system is investigated in both the time and frequency domains.

A novel type of waveguide polarizer with large cross-polar bandwidth

Abstract: A wideband quarter-wave polarizer is presented having a rectangular cross-section, where all four walls are loaded with a dielectric or artificial dielectric. A much larger bandwidth compared to existing polarizers can be obtained without increasing the insertion loss. A polarizer so constructed was fabricated and measured. The polarizer had a differential phase shift within 90 degrees +or-0.7 degrees corresponding to 44 dB isolation, insertion loss below 0.06 dB, and return loss below -24 dB (VSWR >

Neural networks for narrowband and wideband direction finding

Abstract: The authors have investigated the narrowband direction-finding problem with neural networks, and propose taking into consideration several snapshots of array data when programming the network. This yields an average version of the interconnection strengths and bias terms that program the network. Simulation results show that using these averaged interconnection strengths and bias terms enhances the performance of the network compared to the method used by R. Rastogi et al. (1987). The authors extend the direction-finding problem to the wideband case in which the sources have broad temporal frequency spectrum. They utilize the information present at different frequencies in the source spectrum to obtain a suitable cost function that can be minimized by a neural network. >

Simultaneous transmission of 100 Mbit/s at baseband and 60 FM video channels for a wideband optical communication network

Abstract: A wideband optical communication system is demonstrated over 12 km of optical fibre which simultaneously transmits both a 100 Mbit/s baseband digital signal and 60 FM video channels subcarrier multiplexed in the 2.7–5.2 GHz band.

An anticipative adaptive array for frequency-hopping communications

Abstract: To fully utilize the theoretical processing gain achievable when an adaptive array and frequency hopping are combined, frequency compensation is required. Improved versions of an anticipative adaptive array are examined that provide efficient compensation by adapting the complex weights at each antenna element to the appropriate values for a carrier frequency before that frequency is received. The underlying adaptive algorithm used is the maximum algorithm. Computer simulation results are used to compare the different versions of anticipative processing. These results show that an appropriate version ensures the rapid convergence of weights to values that provide wideband nulling of the interference and noise. >

Microwave subcarrier multiplexing: new approach to wideband lightwave systems

Abstract: Wideband communication systems for providing voice, data, and video services to the subscriber over optical fibers are discussed. The principles of microwave-multiplexed lightwave systems are introduced, and several transmission experiments that demonstrate the concepts are described. >

A new architecture for packaging wideband communication equipment using a 3-D, orthogonal edge-to-edge topology

Abstract: Describes a novel physical design for the packaging of communication equipment and shows its advantages as applied to a 256-port, 100-Mb/s Batcher-banyan facility switch. The design uses an orthogonal, edge-to-edge, 3-D topology to streamline the flow of interconnections between stages of the switch and to simplify and shorten lead lengths, thereby increasing the switch speed. A midplane circuit board to 'swap' network leads from orthogonal connectors to chip cards to provide chip-on-board mounting and fanout to the connectors is described. It is concluded that the electrical performance of this structure should support switches operating at speeds well in excess of 200 Mb/s. >

Frequency stabilization in semiconductor lasers

Abstract: Three promising methods of improving temporal coherence in semiconductor lasers are reviewed. They are the development of novel laser devices, a technique of optical feedback and a technique of electrical feedback. The main discussion in this paper is focused on the technique of electrical feedback. The theoretical limit of frequency stability and recent experimental results are presented with respect to the following five subjects which are indispensable in the realization of highly coherent lasers: (a) frequency stabilization; (b) improvements in frequency reproducibility; (c) linewidth reduction; (d) frequency tracking; and (e) stable, accurate and wideband frequency sweep.

Synthesis and design of wideband symmetrical nonuniform directional couplers for MIC applications

Abstract: A computer-aided-design (CAD) synthesis procedure using cubic splines for wideband symmetrical nonuniform directional couplers in inhomogeneous media is presented. Solutions for the potential problems inherent to these couplers are given. Results are presented for a 2-18-GHz, five-section, -3-dB nonuniform tandem directional coupler designed and built on an alumina substrate. >

Low-noise wideband analog optical link using a DFB laser diode

Abstract: For analog optical transmission, the multimode laser diode (LD) has been thought better because of Its low coherence. We report that the link using a distributed feedback laser diode (DFB-LD) single-mode fibers (SMFs), and low- reflection connectors exhibits superior analog transmission characteristics.

Laser instrumentation for one-phonon sensitivity and wide bandwidth with multimode gravitational radiation detectors

Abstract: In a multimode detector of gravitational radiation, the displacements induced in the antenna by the gravitational field can be amplified by many orders at the last resonator. Detection of the displacements of that resonator with a Fabry–Perot interferometer is considered. Quantum and classical sources of noise are analyzed and specifications for laser instrumented massive wideband systems operating at the level of δh=2.6×10−20 and 3×10−22/(Hz)1/2 are given. Three detectors could be used to cover the frequency range ≊400–≊1200 Hz with approximately uniform sensitivity.

Performance of some Rake modems over the non-disturbed wide band HF channel

Abstract: The author presents performance evaluations for four Rake modems used to communicate over the wideband (e.g. 1 MHz) HF channel. Attention is confined to performance for the nondisturbed HF channel. Consideration is given to the impact of mode Doppler shift and multipath spread due to dispersion. The effects of additive noise, self-noise, and imperfect channel measurements are included. Results are presented for decision-directed, parallel probe, serial probe, and DPSK Rake modems. Performance to within 1-3 dB of the additive white Gaussian noise channel is predicted, depending upon the modem and the channel dispersion, if the Doppler shift of the modem can be tracked to within 0.1 Hz. >

Wideband packet technology

Abstract: The authors describes the benefits of wideband packet technology and presents its protocols, performance, and equipment aspects He shows that using proven digital signal processing techniques and standard protocols, wideband packet technology allows the integration of voice/data/image/control onto one self-healing DS1 LAPD network >

Wideband probing of the transauroral HF channel: Solar minimum

Abstract: The Naval Research Laboratory HF Channel Prober is a high-resolution, computer-controlled, coded-pulse sounder designed to study the time variable behavior of the wideband HF radio channel. Multispectral time histories of the channel pulse response and the channel scattering function are tools used in the study. Pulse response delay resolution down to 1 μs and unambiguous Doppler up to ±30 Hz are possible, depending on the choice of experiment format and operating parameters. Measurements were made quarterly between October 1985 and July 1986 on a 2300-km transauroral path between a transmitter site at Frobisher Bay, Canadian Northwest Territories, and a receiver site near Rome, New York. Data are presented in the form of ionograms, pulse response time histories (power and coherent video), and channel scattering functions. Data for mid-latitude and transauroral paths are compared, and their similarities and differences are discussed. The mid-latitude channel is multimodal but is usually characterized by a single specular return per mode. The character of transauroral channel is quite variable, depending strongly on the degree of magnetic disturbance, the location of the midpath reflection point relative to the position of the auroral oval, and the mode. During quiet magnetic conditions, and with the path midpoint well below the auroral oval, channel behavior is shown to resemble a mid-latitude channel at certain times and a specular multipath channel at other times (i.e., one where each mode comprises several distinct multipath components). Doppler spread in these cases tends to be small. At night, when the midpath point lies within the auroral oval, the return signal is diffuse, and the Doppler spread appears to be larger by an order of magnitude.

Design and performance of wideband subcarrier multiplexed lightwave systems

Abstract: The transmission bandwidth of SCM systems is not determined by the availability of electronics, but by the modulation characters of high speed semiconductor lasers. The authors analyze the limitations on SCM systems imposed by laser modulation depth and by second order laser intermodulation products. The performance potential of wideband SCM systems is demonstrated with three systems experiments: a 120 channel FM video transmission using the 2.8-7.6 GHz band; the combination of 60 FM channels and a 100 Mb/s baseband digital signal; and a 20 channel FSK system transmitting 100 Mb/s channel in the 2-6 GHz band. >

Narrowband parameter estimator

Abstract: A narrowband parameter estimator circuit is described which can be used to estimate the frequency and the relative power of narrowband interference tones which reside in a wideband information signal. A two-weight adaptive filter with a phase/frequency-lock loop circuit works in conjunction with a stepped synthesizer to lock onto the individual narrowband interference tones. A lock-detect circuit signals a digital logic unit to record the frequency of the stepped synthesizer and to measure the power in the adaptive filter output signal. This same output signal is used to cancel the unwanted tone in the wideband information signal being transmitted.

A wide band distributed dual gate HEMT mixer

Abstract: The authors present the systematic design, fabrication, and evaluation of a distributed wideband monolithic mixer using dual-gate HEMTs (high-electron-mobility transistors). The circuit was fabricated on an Al-GaAs-GaAs heterostructure wafer. The measurement results show that the mixer operates from 5 to 18 GHz with a conversion loss from 3 to 5 dB. This is believed to be the first reported wideband distributed mixer using dual-gate HEMT devices. The mixer chips developed are key components for EW (electronic warfare) applications. >

Ridged waveguide wide band diplexer with extremely sharp cut-off properties

Abstract: A wideband balanced diplexer splits an incoming wideband microwave frequency signal into separate upper and lower frequency outputs and possesses a sharp band cut-off to increase effective bandwidth. The diplexer includes a pair of waveguide assemblies for separating the upper frequency band from the incoming signal. Each waveguide assembly includes a tuneable, ridged waveguide phase shifter for shifting the phase of the lower frequency band, a reference waveguide for inserting a delay onto the upper frequency signal in order to compensate for the effects of the phase shifter in the other waveguide assembly, and a high pass filter. The high pass filter includes a ridged waveguide having tapered ends of a shape comprising an exponential function raised to a cosine squared power to increase the bandwidth of the upper frequencies and to provide a sharper frequency cut-off.

Sectored-beam multi-signal TWT analysis

Abstract: Harmonic-signal interference is known to degrade the performance of wideband TWTs (traveling wave tubes) When harmonic frequencies occur in the neighborhood of intersection points among spatial harmonics of forward and backward waves of the slow-wave circuit, the deterioration in fundamental power and efficiency can be strongly accentuated To model this multisignal problem, a recast large-signal analysis of traveling-wave interaction involving simultaneous forward and backward waves at frequency harmonics of the fundamental signal has been developed from an existing one-dimensional disk model Coupling to the beam among the spatial harmonics differing in their azimuthal index values is accomplished by partitioning the solid (or annular) beam into constrained sectors (azimuthally and radially), equally spaced initially over the fundamental RF period A computer code based on this upgraded formulation has confirmed the importance of the backward wave in the stop-band-related power absorption phenomenon in TWTs >

Rigorous design of septate E-plane multiplexers with printed circuit elements

Abstract: A compact, low-cost, and low-insertion-loss millimeter-wave multiplexer design is introduced. This design uses metallic E-plane filters integrated in the septate waveguide sections of wideband E-plane n-furcated power dividers. A rigorous simulation technique, which is based on the modal scattering-matrix method, comprises the complete component including the E-plane transformer, i.e. the septum as well as the filter sections, and takes the influences of the higher-order mode interaction at all discontinuities into account. Computer optimized data are given for microwave (14.75-16.25-GHz) and millimeter-wave (74-79.5-GHz) diplexer and triplexer design examples with five-resonator, or seven-resonator metal-insert filters, respectively. >