摘要:

AbstractLong‐term instability is one of many serious problems in Zero‐Forcing (ZF) automatic equalizers for television signals. This paper analyses this problem by solving the tap weight covariance matrix. the result is that the tap weight fluctuation (variance) increases significantly as the input signal bandwidth becomes narrow and/or the number of taps increases. the leakage algorithm which is very effective in reducing the tap weight variance is examined also. In addition, the timing adjustment which is another problem in the ZF algorithm, is examined and it is proved that the leakage algorithm does not improve the instability caused by timing misadjustm

ISSN:8756-6621    

DOI:10.1002/ecja.4400670702

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe problems of testing the planarity of a graph and of embedding a planar graph in a plane arise in many applications. This paper presents a simple linear algorithm for the latter problem. the algorithm is based on the “vertex‐addition algorithm” of Lempel, Even and Cederbaum for planarity testing and is a slight modification of Booth and Lueker's implementation of the testing algorithm using a PQ‐tree. Compared with the embedding algorithm known as the “path‐addition” algorithm of Hopcroft and Tarjan, our algorithm is conceptually simple and easy to understand

ISSN:8756-6621    

DOI:10.1002/ecja.4400670703

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

年代:1984

数据来源: WILEY

摘要:

AbstractWe have investigated correlations between an ambient temperature and a frequency of a 5‐MHz, 5th overtone IC‐cut plano‐convex quartz oscillator. We found that the spectral density of frequency fluctuations is composed of three parts over a fluctuation frequency from 10−6to 10−2Hz; in the lowest frequency part it is proportional to 1/f2, which continues to 1/f and eventually to f0. the 1/f2and f0spectra are caused by ambient temperature fluctuations. Thus we have found that the 1/f spectrum has nothing to do with temperature fluctuations, which, therefore, provides a limit for frequency stability of a quartz o

ISSN:8756-6621    

DOI:10.1002/ecja.4400670704

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

年代:1984

数据来源: WILEY

摘要:

AbstractPreviously, we reported a method (the previous method) for estimating by successive iterations electron density profile in the D layer in which if the absolute phase of the ionospheric reflection coefficient for the VLF wave is known, the perturbation of the reflection coefficient is found to solve the integral equation or the perturbation of the electron density by full‐wave analysis. In the present paper, the previous method has been studied theoretically and the following methods adopted: 1) successive calculation at each frequency; 2) restriction of the computed perturbation of the electron density and the successive extension to the altitude range for the corrected values of the electron density by use of the restricted value; 3) smoothing of the computed density by use of the restricted value; 3) smoothing of the computed results of the electron density; and 4) use of specific initial profile of the electron density. These methods have been applied to the exponential distributions and the measured profiles and simulations have been performed. Improved results over the previous method have been obtained. For instance, the cases that could not have been estimated by the previous method can now be estimated. the estimation range has been increased or the accuracy improve

ISSN:8756-6621    

DOI:10.1002/ecja.4400670705

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

年代:1984

数据来源: WILEY

摘要:

AbstractPhased array reflector antennas are used in practice for beam scanning in a limiting range of angles. Compared with the complete phased array systems, these antennas have a simple structure and can be constructed with a smaller cost. These arrayss fed reflector antennas can be replaced with generalized array antennas by considering the secondary radiation pattern of each feeding element of the array element pattern. This paper is a theoretical study of the maximization of the gain and suppression of the sidelobes for this generalizeed array. These problems are important for pattern synthesis. From the study, it was found that the computation time of the synthesized secondary pattern can be reduced for the array fed reflector antenna due to exploitation of the secondary element patterns. Also, the array excitation distribution optimum for the desired pattern can easily be determined from the theory of the generalized array. These findings have been confirmed experimentally by means of an X‐band linear array fed reflector antenn

ISSN:8756-6621    

DOI:10.1002/ecja.4400670706

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

年代:1984

数据来源: WILEY

摘要:

AbstractHigh‐speed waveform transmission is of great importance in the realization of digital radio systems with high spectrum utilization efficiency. the binary transversal filter (BTF) offers an effective technique for achieving high‐precision waveform generation because it is a means of producing the desired waveform directly in the time domain. This paper presents a new technique for design of the BTF and discusses the authors' experimental results. the new BTF can be applied quite easily to high‐speed multilevel signals and is composed of a shift register, a programmable ROM (PROM) and a D/A converter which are driven by a multiphase clock. A was used to design the basic parameters of the BTF: sampling frequency, number of taps and tap coefficients, quantization levels for the D/A converter and allowable phase error for the clock signal. an analysis was conducted to determine the effect that each factor has the spectral characteristics and intersymbol interference characteristics. Further it was shown that based on this configuration and design method, a 12.5‐MB 4‐level Nyquist waveform can be realized without a

ISSN:8756-6621    

DOI:10.1002/ecja.4400670707

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

年代:1984

数据来源: WILEY

摘要:

AbstractRecently, many attempts have been made to increase the bandwidth and the gain of circularly polarized antennas constructed on printed circuit boards. In a previous paper, a wide bandwidth was achieved for a circularly polarized array antenna composed of strip dipoles and slots (CP‐PASS), although its actual gain was rather low. In the present paper, the gain of CP‐PASS is enhanced by adopting an end‐fed strip dipole as a strip element, and a basic design procedure and some experimental results of CP‐PASS are shown. First, it is verified by experiments that the end‐fed strip dipole has some advantages; for example, it has a sufficient gain, its crosspolar radiation level is low, and it is easy to control the radiation resistance. Second, an approximate analysis is made for a basic radiating‐element pair for CP‐PASS, and a basic design procedure of CP‐PASS is obtained by applying the analysis. Finally, several CP‐PASS are made and measured, and the design procedure is found to be useful. For a six‐pair CP‐PASS, its actual gain, 3‐dB gain bandwidth, and axial‐ratio bandwidth are about 12 dBi, 11% and 12%, respectively. It is found also that CP‐PASS requires only a slight correction to the element lengths when a reflector is placed. In addition, it is obtained that the gain of CP‐

ISSN:8756-6621    

DOI:10.1002/ecja.4400670708

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

年代:1984

数据来源: WILEY

摘要:

AbstractAlthough the conventional spread‐spectrum communication system has the advantage of asynchronous multiple‐access, the number of simultaneously communicable channels is small due to the interchannel interference and the efficiency of frequency utilization is very low. to deal with this problem, this paper proposes a new synchronous spread‐spectrum multiplex communication system employing a modified M‐sequence. the modified M‐sequence is derived by giving an appropriate dc offset to an M‐sequence so that the sidelobe of its autocorrelation function becomes zero. In this system bitshifted modified M‐sequences are used as spreading codes for each channel and the synchronization among them is maintained. Let N be the length of the spreading code. If a bandwidth N times as large as that required for one channel transmission is used, and the product of the band‐limiting characteristics and the power spectral density of the spreading code satisfies Nyquist's first criterion, multiplex transmission of N channels is realized without interchannel interference. It is proved that equally chosen filters for the transmitter and the receiver to realize the transmission bandwidth restriction maximize the SN ratio due to noise in the transmission channel and the value becomes equal to that in the one‐channel transmission. Therefore, the same number of channels as in TDM is achieved with the same SN ratio and the efficiency of frequency utilization is improved greatly. As for synchronization, almost the same bit synchronization error as

ISSN:8756-6621    

DOI:10.1002/ecja.4400670709

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

年代:1984

数据来源: WILEY

摘要:

AbstractIn maritime satellite communications, the fading of the satellite direct wave due to interference from sea return waves is a serious problem which causes difficulties in the communications. As a result, methods of reducing the effect of sea return waves have recently been investigated. This paper proposes an antenna configuration that permits such fading effects to be reduced by controlling the polarization for waves in the direction of the sea return wave (we call it “the reserved direction”). At the same time, the polarization loss for the satellite direct wave is made small. the present configuration is composed of a pair of dipole antennas with a reflector. Controls of these wave sources (current distributions) enable us to synthesize the polarization in the reserved direction which is in opposite sense of rotation with that of the sea return wave, has the same axis ratio, and whose major axis is orthogonal to that of the sea return wave in the reserved direction. This reduces the fading effects greatly. Furthermore, even when the antenna shows a movement according to the vessel movement, we have adopted a system which corrects electrically the antenna fluctuation resulting in saving the mechanical altitude stabilizing equipment. We describe first the fundamental characteristics of the present antenna configuration. Wave source characteristics for controlling the polarization in the reserved direction for simple examples have been presented, along with the theoretically computed results of the axis ratio and radiation pattern, etc. Finally, the results of model experiments have been presented to support the theoretical considerati

ISSN:8756-6621    

DOI:10.1002/ecja.4400670710

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

年代:1984

数据来源: WILEY

摘要:

AbstractThis paper analyzes the mechanical and electrical characteristics of the hand‐twisted conductor splices in communication cables. the validity of the analysis is verified by experiment. Concerning the mechanical characteristics, it is shown that in the physical contact of the conductors the central axis is twisted with an arbitrary pitch angle on a quasi‐cylinder with the radius equal to that of the conductor. Based on such representation of the contact mechanism, the contact pressure and contact width of the twisted conductors are calculated. Concerning the electrical characteristics, it is assumed that there is a similarity between the current distribution through the twisted conductor contact and the electric lines of force produced by the charge on the surface of contact. Based on such assumption, the constriction resistance of the twisted contact is calculated with consideration of the contact pressure and contact width. Estimation is also made on the growth process of the film resistance and the boundary film thickness due to the chemical substances formed on the conductors in contact. the electrical equivalent circuit for the twisted conductor contact is derived, including the constriction resistance, film resistance and conductor resistance. Using the derived equivalent circuit, an expression is derived for estimation of the contact resistance of the twisted conduct

ISSN:8756-6621    

DOI:10.1002/ecja.4400670711

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

年代:1984

数据来源: WILEY