摘要:

AbstractLead‐acid batteries have been used as emergency back‐up power supplies for communication systems. These batteries usually are charged and provide power to communication systems when a power blackout occurs. If the communication system is out of order during the blackout, the problems can be enormous. Therefore, NTT has been serious about the maintenance of the lead‐acid batteries.Since it takes longer than 20 hours to check the capacity of a battery, some other convenient battery evaluation method must be established. In this paper, the degradation mechanism of the lead‐acid battery was studied and it was concluded that the degradation of the internal resistance is related strongly to the capacity degradation. By measuring the internal resistance, the charge/discharge characteristics were evaluated for a short period of time.It was confirmed also that the internal resistance measured by measuring the charge/discharge characteristic for a period shorter than 500 ps is related strongly to the battery capacity. Using the forementioned relationship, the battery degradation was det

ISSN:8756-6621    

DOI:10.1002/ecja.4410771001

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper proposes a new asynchronous transfer mode (ATM) switch architecture called a “barrel switch.” The barrel switch is constructed fromn/2×nidentical element switches which are placed out around a cylinder and connected to each other.The features of this proposed switch are as follows.1. This switch has an architecture suitable for high‐speed (2.4 Gbps and more) cell switching.2. It is a multistage self‐routing and nonblocking switch.3. Copy connections can be realized with this switch.4. The building‐block method is applicable to switch implementation, which ensures a full scalability.Cell loss rate and delay characteristics of this switch also are discussed using computer simulation results. Simulation results under random traffic prove that a 64 × 64 barrel switch has adequate cell loss rate and mean delay characteristics to an actual ATM switc

ISSN:8756-6621    

DOI:10.1002/ecja.4410771002

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper describes a very high‐speed coding and decoding processor Image Pipeline Codec (ImPC, MN86063), which can be applied to bi‐level image, focusing on the architectural design and performance evaluations. An application example for a facsimile apparatus also is presented.The ImPC integrates basic functions required for an advanced facsimile such as two‐channel encoding and decoding, resolution conversion, and direct memory access (DMA) transfer functions. The ImPC includes the redundancy reduction coding algorithms modified Huffman (MH), modified READ (MR), modified MR (MMR), and an original coding scheme. A line of 4096 alternating black and white pixels can be encoded or decoded in 0.84 ms with 100‐ns cycle time. A typical A4 size office document is processed in 0.17 s. The ImPC chip is fabricated using 1.2 μ CMOS technology, integrating approximately 480,000 transistors on a 9

ISSN:8756-6621    

DOI:10.1002/ecja.4410771003

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

年代:1994

数据来源: WILEY

摘要:

AbstractRecently, with the diversification of electromagnetic compatibility (EMC) problems, the need for an electric field sensor to measure the electromagnetic pulses and the electric field near the equipment has increased greatly. An electric field sensor using LiNbO3, which has an electrooptical effect, has been used for such measurements; but the sensitivity is not satisfactory. However, the sensitivity can be improved by increasing the sensitivity of the optical modulator or by increasing the output of the optical modulator source.Here, we describe a method to improve the sensitivity at resonance frequency by loading inductance. First, an equivalent circuit representing the sensor with loading inductance is derived. Second, the frequency characteristics are analyzed theoretically by applying the moment method to this equivalent circuit and the improvement in sensitivity by loading inductance is demonstrated. Moreover, the validity of analysis is confirmed by performing the experiments using the GTEM‐cell.As a result, it is found that the measured results show good agreement with the calculated results and the sensitivity can be improved by inductance loading. It has been confirmed that the sensitivity of the electric field sensor with element length of 150 mm could be improved by about 40 dB at 200 MHz by using the loading inductance of 600 n

ISSN:8756-6621    

DOI:10.1002/ecja.4410771004

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

年代:1994

数据来源: WILEY

摘要:

AbstractWhen the synthetic aperture method is applied to the imaging of objects in the front direction of a moving vehicle, a problem arises in that, if the objects are at positions symmetrical to the direction of movement, the Doppler frequencies change in the same way. Consequently, ghosts symmetrical to the axis are produced in the reconstructed image. From another viewpoint, when an object exists in the direction perpendicular to the direction of movement, the change of the Doppler frequency depends on the position of the object. Then the rate of change is not kept constant and the processing based on the FFT algorithm, as in the general cases of synthetic aperture radar and long‐wavelength holography, cannot be employed.This paper proposes an imaging method for the front‐looking radar based on the principle of long‐wave‐length holography. The proposed method can solve the ghost problem for the objects symmetrical to the direction of movement using a small number of antennas in the azimuth direction. An algorithm also is proposed for high‐speed image reconstruction from the data acquired by the system. The theoretical resolution and the range of maximum possible imaging are discussed. Furthermore, the validity of the proposed method is verified by a computer simulation and an experiment using m

ISSN:8756-6621    

DOI:10.1002/ecja.4410771005

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

年代:1994

数据来源: WILEY

摘要:

AbstractWith the recent development of satellite communication and the diversified demands for communication, there has been increasing demand to utilize the position of the mobile object as the information. This idea is proposed and has been developed in various countries of the world as the radio determination satellite system (RDSS).This paper outlines the hybrid communication/ positioning system using two geostationary satellites. The system has been developed by the Communication Research Laboratory in collaboration with the R&D Center for Radio System, together with the result of basic experiments.Two kinds of experimental systems with different modulation/demodulation methods are constructed. One is the method based on the offset QPSK (called SCPC), and the other is based on the spread‐spectrum (called SS). The former transmits the narrowband signal for distance measurement, in addition to the communication signal. Consequently, this method can easily be introduced into the SCPC satellite communication system presently used in practice, although the accuracy of the positioning is slightly deteriorated. Compared to the former, the latter has the advantage that a highly accurate positioning can be realized since a high‐speed positioning signal is employed using a wide transmission bandwidth. However, the system configuration becomes complex. A field experiment is conducted for each system using theEngineering Test Satellite V(ETS‐V) and theInmarsatsatellite. The positioning accuracy of 2 to 8 km for low altitude and 1 to 2 km for middle altitude is obtained in SCPC. The position accuracy of 400 to 600 m is obtained near Japan

ISSN:8756-6621    

DOI:10.1002/ecja.4410771006

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

年代:1994

数据来源: WILEY

摘要:

AbstractWhen observation of a direct lightning strike to a building is performed or in an experiment for applying lightning using a building, one needs current sensors that can measure the current in building columns, girders, and walls. As the current sensor, the Rogowski coil commonly is used. The coil is placed around the object to be measured, and the inductive voltage is obtained. Although there are many commercially available units, these sensors are too small for measuring building columns and girders.This paper studies Rogowski coils which are long enough to encircle the building columns and girders and flexible enough to set up the structure according to the practical situation. First, the coil and the integrator are described by their lumped element equivalent circuits. In addition, the target values were set for the frequency bandwidth and the sensitivity. A structure optimum for these characteristics was found. From the results, a hollow core coil using a vinyl pipe was fabricated. A Rogowski coil 1 to 10 m long was realized which has a frequency of 300 kHz and a current‐voltage conversion factor of 1/100. Further, the position dependence of the current to be measured was observed. Sufficiently practical characteristics were obtained with the present coil with a long structur

ISSN:8756-6621    

DOI:10.1002/ecja.4410771007

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe configuration and function of a surface acoustic wave (SAW) filter matrix used on board a satellite to implement a subchannel switched FDMA (SS/FDMA) system is described. The function and configuration of the SAW filter matrix (SFM) are described. Conditions imposed on the amplitude and phase of two adjacent subchannels to provide a broad channel by combining the outputs of the subchannels are investigated. Electrical and transmission characteristics of an SAW filter matrix used in four‐beam SS/FDMA system with a subchannel‐combining function are presented, demonstrating its technical feasibility.When implementing an SFM, it is important that the devices used for a satellite‐based SS/FDMA router are sufficiently reliable for the design life of the satellite. A methodology is shown that gives a redundant configuration with the lightest mass and that achieves the targeted reliability. Example calculations for a four‐beam SS/FDMA router ar

ISSN:8756-6621    

DOI:10.1002/ecja.4410771008

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe fundamental importance of the Yagi‐Uda antenna is its structural simplicity and its director and reflector actions. To fully comprehend the working principle of this antenna, it is important to be able to visualize the radiation mechanism directly in the time domain. In this paper, transient analysis of the Yagi‐Uda antenna is performed using the FD‐TD method. First, the input impedances and directivities obtained by this method are compared with the moment method, good agreement was found between the two methods, and the validity of this method was demonstrated. Next, the quasi‐impulse responses of the antenna are calculated. The field pattern obtained by this method was visualized in the time domain. The radiation from the antenna edge is shown in the early time responses, and dispersion of the pulse shape with the passage of time is shown in late time responses. Moreover, the difference of characteristics due to the length of parasitic elements is shown by time‐domain ob

ISSN:8756-6621    

DOI:10.1002/ecja.4410771009

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

年代:1994

数据来源: WILEY

摘要:

AbstractA novel ferrite grid electromagnetic wave absorber composed of sintered ferrite is proposed. Based on the condition that the return loss should be above 20 dB at 30 MHz, its wideband characteristics for suppressing reflections compared to a single‐layer absorber are demonstrated by computer simulation.Calculating the return loss by varying the geometrical parameters of the ferrite grid, an optimum structure is determined which gives the maximum frequency band. In addition, it is found that the return loss of the grid absorber is impaired by an air gap between the ferrite and conductor. Moreover, the operating characteristics of the grid absorber are demonstrated by experimental model

ISSN:8756-6621    

DOI:10.1002/ecja.4410771010

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

年代:1994

数据来源: WILEY