摘要:

AbstractIn this paper we propose a new method for an economical and realizable null synthesis to prevent interference between wireless communication lines and mixing with interfering waves. Existing methods are based on the principle of a subtraction of the directivity of a cancelling beam which has a maximum value along the prescribed null direction from that of the original array. These methods cannot avoid a degradation of the directivity in directions other than the null direction.In this paper we have applied the concept of an array of the arrays. We have synthesized nulls by the array factor of an (M + 1) element array which has M nulls in the directivity of an N element array. In total, we used M + N elements for the array. This method depends on the principle of the products of directivities.As long as the null direction is far removed from the main beam direction, there is, in principle, no degradation of the array directivity. By approximating element weights, we can synthesize nulls by controlling the weights of only terminal 2M elements. Past methods have noted experimentally a possible null synthesis by controlling the weights of the terminal elements.This paper provides clearly for the first time its theoretical reason and limits. We have applied the present analysis method for cases of Taylor directivity for the side‐lobe level ‐30 dB for n = 5 in a linear array with elements placed one‐half wavelength apart. We show calculations in examples for syntheses of cases of one null and two nulls. We found that by synthesizing two symmetric nulls with respect to the main beam, there was almost no degradation of the array direct

ISSN:8756-6621    

DOI:10.1002/ecja.4410730501

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe scattering problem is analyzed in the case where an electromagnetic wave is incident on a perfectly conducting rectangular cylinder located near the conducting plane. Since it is difficult to solve this problem directly as the boundary value problem, the problem is replaced with that of scattering by two conducting rectangular cylinders by means of the method of electrical image. The analysis is based on the point matching method and the amount of computation is reduced by reducing the number of simultaneous equations derived from the boundary conditions into one‐half by using the symmetry of the electromagnetic field. As the numerical examples, the near field and the scattering patterns are presented which have not been reported often. Numerical results are compared for the perfectly conducting circular cylinder located near the conducting plane with those of the rectangular cylinder. To confirm the theory, a model experiment is conducted at microwave frequencies so that reliability of the theory is teste

ISSN:8756-6621    

DOI:10.1002/ecja.4410730502

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

年代:1990

数据来源: WILEY

摘要:

AbstractWith the advance of telematic technology, increasing document image information utilized in the state of soft copy is expected. In these situations, copies of obtained document image information are made illegally with ease, and hence the validity authentication of the information itself and its provider becomes more necessary. Since document image information to be authenticated exists in a form which can be read at an unidentified number of receiver terminals, the realization of an authentication scheme where document image and signature are combined is necessary. This is characteristic of document image information including nature pictures and photographs.This paper proposes a new concept of signature, which is called “digital watermark” for document image communication. A digital watermark is the coding scheme in which secret information is embedded into a document image similar to a watermark. Image coding schemes already proposed are available to realize a digital watermark. We present a method of obtaining a digital watermark using a well‐known predictive coding algorithm. Also, we define a criterion for security and show to what extent the digital signature is safe using simulation results, where two or three illegal actions are consi

ISSN:8756-6621    

DOI:10.1002/ecja.4410730503

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

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper describes the behavior of the processing element (PE) generally used in applying the data‐flow control scheme to signal processing equipment in the switching system or in the computer system. A performance evaluation is presented in terms of the characteristics based on the theoretical analysis. It is important in this scheme to evaluate the time until the program execution is completed (program execution time) for the given parallelism of the data‐flow program and the multiplicity of the program (task). As a preliminary to the estimation of the program execution time, this paper evaluates PE as a whole.First, the matching‐store unit of PE is considered. A simple numerical analysis based on the traffic model is presented and the performance is evaluated. The characteristics such as the mean number of waiting calls and the mean waiting time are calculated. Using those results, the whole PE is modeled as a BCMP‐type queueing network, and the mean cycle time is derived. Finally, the result of numerical calculation and the result of simulation are illustrated. The range of application is described, together with some disc

ISSN:8756-6621    

DOI:10.1002/ecja.4410730504

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

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper proposes a new duplex modified‐READ (MR) coding scheme for transmitting a facsimile picture on which other information can be embedded. When the vertical mode on the coding‐scanning line is coded, the MR coding is carried out by moving the run‐length of a black or white pel using the bit‐series of an information source to be duplexed. This method offers a facsimile picture which has almost the same quality as its original without increasing the quantity of the MR‐coding, and can transmit the second information without notice by a third person. For example, the second information with 2 k to 14 kbytes can be transmitted with one of the CCITT test documents. This is an answer to conventional facsimile systems which have a lack of secrecy. This method also contributes to double the transmission rate so that transmission lines can be used more ef

ISSN:8756-6621    

DOI:10.1002/ecja.4410730505

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe trunk‐reservation scheme is employed to specify the individual call loss in the alternative routing system. The numerical solution of the state equation and the simulation has been used traditionally for the optimum design of such a system. This paper presents the optimum (in the sense of the minimum cost) design of the alternative routing system with the trunk‐reservation scheme, using the approximate expression for the individual call loss and its derivatives. A method is presented also to obtain the optimum integer number of trunks. By an example, it is shown that the presented method of the optimum design can reduce the computation time drastically and provides a good approximation compared with the past methods by state equation or simulat

ISSN:8756-6621    

DOI:10.1002/ecja.4410730506

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

年代:1990

数据来源: WILEY

摘要:

AbstractIt has been known for a long time that the intensities of the whistlers observed on the ground sometime exhibit frequency dependence through analyses of sonograms. The frequency dependence of the intensities of whistlers observed at low altitudes was examined in detail with the aid of a PCM recorder and FFT analysis. As a result, whistlers were found whose intensity spectra were independent of the frequency spectra of their causative atmospherics. In other words, the changes of the received signal intensities of each whistler with respect to the frequency had patchy patterns. This paper describes various characteristics of patched whistlers. For their interpretation it is proposed that their generation was due to the wave interference by the irregularities of electron densities in the F‐layer ionospher

ISSN:8756-6621    

DOI:10.1002/ecja.4410730507

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

年代:1990

数据来源: WILEY

摘要:

AbstractOf the VORs providing directional information to aircraft, the new DSB‐type Doppler VOR has recently been employed as the domestic standard. In this system, the required receiving signal is obtained in the far field whereas the received signal is distorted if it is received near the VOR station. On the other hand, when a VOR station is installed, it is difficult to secure a larger area than the present one because the acquisition cost of the land is high and selection of the land becomes even more difficult if the traditional land requirement is modified. Therefore, the receiving antenna for monitoring the operating condition and the performance of the equipment is often installed near the VOR antenna so that the signal can be distorted for accurate monitoring unless an appropriate distance is maintained.This paper studies a method in which the DSB‐type Doppler VOR can be monitored even if the receiving distance is short. The circuit configuration is complicated in the method in which the phase of the carrier being received is forced to follow the phase change of the side band signal. Instead, this paper proposes a method for simplifying the circuit configuration by replacing the carrier wave with a new carrier with an appropriate fixed phase, and an experiment is carried out. It is found that the distortion is reduced significantly and a VOR direction characteristic close to the case for a far field reception even with a short receiving distance is obtai

ISSN:8756-6621    

DOI:10.1002/ecja.4410730508

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

年代:1990

数据来源: WILEY

摘要:

AbstractAs a model for the electromagnetic wave propagation in a tunnel‐shaped structure with branches and bends such as an underground shopping center and a street lined with buildings, a two‐dimensional tunnel with modified multicross junctions is studied both theoretically and experimentally for wave propagation. The basis of the theoretical analysis is to neglect the higher‐order multiple scattering effect and to consider the field as the cascaded connection of the results of the modified single‐cross junction. As the boundary condition of the tunnel wall, the surface impedance approximation is employed. The present results can be applied to special tunnels made of cascaded connection of the modified cross, step and T. In the experiment, a microwave simulation is carried out for a tunnel model made of concrete. It is found that the numerical results of the electric field intensity in the tunnel agree well with the experimental

ISSN:8756-6621    

DOI:10.1002/ecja.4410730509

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn designing a mobile communication system in suburban areas, it is necessary to estimate electric field strengths in open and suburban areas. We measured field strengths in the 150/900‐MHz band in open desert areas and in the 900‐MHz band in suburban areas in the Middle East region, and open and suburban areas in Kumamoto and Okayama prefectures in the 280‐MHz band.Using these results, this paper discusses the relationship between the median values of the field strengths and distances and their frequency characteristics. As a result, it was found that the average values of measured field strengths at various sites were smaller than the theoretical values of a flat earth model. The field strengths decreased with the squares of distance. This trend agreed generally with the similar relation for the flat earth model.An empirical equation was derived for the correction factor of the electric field strength which is to be multiplied by the theoretical equation of the flat earth model. Quasi‐theoretical and quasi‐experimental equations were obtained for the estimation of the median values of the field strength of long intervals in the VHF/UHF band for flat open areas and suburban zones. With these equations we can estimate the median values of the field strengths of long intervals in open areas (desert, grassy lands and vegetated regions) and suburban areas with scattered buildings and trees, using frequency, the antenna height of the transmitter and distance as p

ISSN:8756-6621    

DOI:10.1002/ecja.4410730510

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

年代:1990

数据来源: WILEY