摘要:

AbstractIn the design of concentration and distribution stages of analog video signal systems, the use of broadband analog switches helps to reduce the number of expensive bandwidth‐reduction CODECs. However, these switches must satisfy severe crosstalk attenuation requirements. To suppress the crosstalk, switch components and packaging must be chosen carefully and switch configurations and their implementation must also be considered. Moreover, the conventional design for one‐to‐one crosstalk cannot be applied to a distribution service for video signals, and a more detailed design that considers crosstalk phase conditions is required. However, no method of allocating the crosstalk attenuation objective to each component in the switch has yet been established for connecting one inlet to multiple outlets.This paper presents a model for crosstalk addition based on the generation mechanism of crosstalk and proposes the concept of equivalent power sum multiplicity. Using this model and concept, a method is proposed of allocating a crosstalk attenuation objective to each component of the switch in order to satisfy the overall qu

ISSN:8756-6621    

DOI:10.1002/ecja.4410770101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractIn order to elucidate the incident pulsed power limit in coherent optical time domain reflectometry (OTDR) using erbium‐doped optical fiber amplifiers (EDFA), experimental data on the nonlinear optical phenomena in a single‐mode optical fiber by a high‐power coherent optical pulse and the resultant degradation of the coherent OTDR are presented and discussed. Previously, the stimulated Brillouin scattering and the stimulated Raman scattering have been considered as the limiting factors for the incident pulse power. However, two nonlinear optical phenomena have been observed which occur at power levels lower than the critical powers of the two phenomena.For a pulsewidth of 1 μs, the intensity gradient occurs in the incident pulse due to reduction of the inversion profile in the EDFA, and an optical frequency shift of the optical pulse occurs in the test optical fiber by the self‐phase modulation. As a result, the beat frequency of the back‐scattered light and the local frequency light falls outside the receiver bandwidth of the coherent OTDR.For a pulsewidth of 100 ns, the intensity gradient of the optical pulse is small, as is the effect of the self‐phase modulation. However, the incident pulse induces a 4‐wave mixing with the spontaneous emission from the EDFA and is transformed to the Stokes light and anti‐Stokes light. Hence, the backscattered light intensity within the receiver bandwidth is decreased, and the performance of the coherent OTDR is degraded. The foregoing results provide important guidelines for understanding the performance limitation of t

ISSN:8756-6621    

DOI:10.1002/ecja.4410770102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractBecause of the progress in optical communication technology, understanding the propagation characteristic of optical fibers has become very important. In particular, since optical networks have been used widely, the evaluation of optical fibers in the field is essential.This paper describes the measurement of the chromatic dispersion of optical fibers and a system suitable for the measurement in the field. The approach is based on the baseband phase‐comparison method. First, the conditions required for this measurement system will be clarified. Then the measurement of wavelengths and wavelength separation satisfying the requirements will be obtained by simulation. The source of each wavelength must be modulated.However, to increase the fiber length and to improve measurement precision, a modulation method based on multiple sinusoidal waves will be proposed, and the upper and lower limit of the optimum modulation frequency will be clarified. The measurement system will be constructed from these results. The technical problems in realizing the system will be shown.Finally, an example of data measured by the constructed system will be shown, and it will be demonstrated that a resolution of 0.01 ps/nm/km and measurement precision of ± 0.3 ps/nm/km can be achieved at wavelengths of 1.3 and 1.55

ISSN:8756-6621    

DOI:10.1002/ecja.4410770103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractOptimization of an antenna for magnetic resonance imaging (MRI) requires an accurate analysis of antennas located inside a conducting cylindrical RF shield. A Galerkin‐moment method analysis which can be used for an arbitrary‐shaped shield is used. The surface current on a conducting plane is expanded by means of surface patch segments based on Richmond's method. Numerical results are compared with measured input impedance, which confirms the validity of the proposed method. Furthermore, a relation between the dimension of shield and the sensitivity of the antenna is discussed theoretica

ISSN:8756-6621    

DOI:10.1002/ecja.4410770104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractTo realize the desired aperture distribution in a radial line slot antenna (RLSA), accurate evaluation of the coupling, guided wavelength and radiation phase of slot sets are required. Moreover, for the slot set similarly to the linearly polarized RLSA whose reflection is essentially large, reflection from one slot set should be reduced sufficiently to realize the desired traveling wave operation; therefore, the reflection coefficient should also be evaluated.In this paper, the scattering matrix equivalent circuit of the slot set is presented for the design of the radial line slot antenna. Using this equivalent circuit, the slot set configuration can be optimized for reflection characteristics, and it becomes possible to realize traveling wave operation with arbitrary polarization.Compared with the conventional analysis assuming uniform slot array, this method has greatly reduced the computation time, and the analysis and design of the antenna has become possible. This analysis has established first the designing of a RLSA with arbitrary polarization.

ISSN:8756-6621    

DOI:10.1002/ecja.4410770105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractUnwanted radar echos, called clutter, make the detection of a target difficult. Therefore various methods have been proposed to suppress such clutters. However, since most of these methods are intended to improve single‐pulse detection performance, the target often disappears by pulse‐to‐pulse fluctuations.In this paper, as a method of suppressing radar clutter, an application of a moving average and a weighted moving average to the data after pulse integration is proposed. First, with theK‐distribution model proposed for modeling the clutter, the signal‐to‐clutter ratio is obtained in the case where infinite pulses are integrated. Next, a method is shown for derivation of the weights to be used for the weighted moving average. The results are shown for the process, using these weights for the sea clutter observed with anX‐band radar. By using the moving average method in the experiment with anX‐band radar, the signal‐to‐clutter ratio is improved by 4.2 dB compared with mere threshold detection, whereas the weighted moving average provides 5.0 dB improvement, which gives

ISSN:8756-6621    

DOI:10.1002/ecja.4410770106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractSince most electromagnetic malfunctions are of high speed and of a passing nature, it is difficult to specify the cause. The objective of this paper is to propose a monitoring system which can detect the electromagnetic waves in the time domain when malfunctions of electrical equipment occurs. The peak value of the detected waveform, the duration of the waveform, and the energy in an arbitrary frequency region were used as procedures to evaluate the measurement data. In this system, by integrating, the energy is defined as the energy spectrum of the detected waveform over arbitrary frequency regions.The monitoring system fabricated for trial was investigated in terms of the processing time such as the data transfer time. It was confirmed that almost 1 s is needed for storing the measured data and that this time duration is the maximum delay in the control of the present system.Using the transmission module as the equipment under test, we performed an experiment to apply the lightning surge on a building which simulates a telephone exchange office to verify the effectiveness of the monitoring system. The measurement results indicate that the amplitude and the energy of the current waveform flowing into the equipment from the grounding wire become several ten times those from other lines. As a result, the detected waveform raised the possibility of significant cause of trouble to the equipment.

ISSN:8756-6621    

DOI:10.1002/ecja.4410770107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractOptimization of an antenna for magnetic resonance imaging (MRI) requires an accurate analysis of antennas loaded by a human body. We have developed a computer code for obtaining the current distribution on the antenna loaded by a human model with an arbitrary geometry and material properties by incorporating the impedance method into the Richmond method. Numerical results for the input impedance are compared with measured impedances confirning the validity of the proposed method. Furthermore, sensitivity. distributions of antennas loaded by a human model are calculated.

ISSN:8756-6621    

DOI:10.1002/ecja.4410770108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractIn conjunction with a recent increase in information density, radio wave communication becomes more complex and more varied. Hence, effective use of radio wave resources is required. Under such a situation, the frequency‐selective screen (FSS) with which a single antenna is capable of receiving multifrequencies at the same time has drawn attention. The FSS consists of conductors placed periodically on a dielectric substrate.In this paper, the spectral domain moment method is applied to the problem of scattering from infinitely many conductors with arbitrary shaped elements on a semiinfinite dielectric substrate. From the results, the effect of the surface resistance of the conductor and the characteristics due to the conductor shape are investigated. Various scattering characteristics by linearly and circularly polarized incidences are discusse

ISSN:8756-6621    

DOI:10.1002/ecja.4410770109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractIn a satellite‐borne large deployable antenna, a mesh‐reflecting surface is used as a reflector material. Its electrical characteristic is an important factor determining the antenna characteristics.In this paper, a measurement system and a measurement method are presented for the transmission loss and the reflection loss of the mesh‐reflecting surface, and an error analysis is made. With a planar mesh made of doubly inlaid knitting of gold‐plated molybdenum wires with a diameter of 30 μm, the transmission loss and the reflection loss are measured systematically, and the data are evaluated. The loss characteristics due to the anisotropy of the mesh and to the dependence on the incident angle and the polarization are found.Further, it is shown experimentally that a loss other than the transmission loss and the reflection loss exists. A quantitative evaluation is made. It is shown that an incident angle dependence exists. A concept of a strip‐aperture model mesh is introduced which simplifies the actual mesh. By comparison with the measured results, the parameters for the strip‐aperture model are determined. Subsequently, the relationship between the actual mesh and the model mesh

ISSN:8756-6621    

DOI:10.1002/ecja.4410770110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY