摘要:

The results of applying the Fredholm integral equation method of solution to the scattering of electromagnetic radiation from oblate spheroidal raindrops for the communication bands 4, 6, 11, 14, 20, 30 GHz are presented in the paper. These scattering amplitudes are then used to calculate propagation characteristics such as attenuation, phase rotation and crosspolarisation of a rain-filled medium. The validity of using the Van de Hulst single-scattering equation is considered, and conditions for its use presented. A new and more general relationship between horizontal and oblique propagation characteristics is presented which uses only the horizontal and zenith conditions to derive all others. Using Brussard's meteorological model for raindrops a new and more general model for the medium containing canted raindrops is presented. Attenuation and crosspolarisation equations are derived for both linear and circular polarisation for this model, which assumes a stochastic model for the canting-angle variations. Finally, the specific cases of terrestrial radio-relay links and satellite communication links are considered, and detailed results presented for each. A comparison of the theoretical results with experimental results for linear and circular depolarisation at 11 GHz is also given.

DOI:10.1049/piee.1977.0078

出版商:IEE    

年代:1977

数据来源: IET

摘要:

A method is presented for determining continuous impedance loading along a cylindrical antenna of given dimensions, which approximately results in certain desired properties of the antenna. The essence of the method consists in assuming a dependence of the impedance loading on the length of the antenna, in the form of power series with unknown coefficients, and determining these coefficients by minimising a convenient function. Numerical examples show good agreement between computed results and available experimental data, and indicate that antennas having different desired properties can efficiently be synthesised by this method.

DOI:10.1049/piee.1977.0079

出版商:IEE    

年代:1977

数据来源: IET

摘要:

A theoretical-numerical technique is developed to solve for the current distributions and, hence, for the field patterns of perfectly conducting antenna structures composed of a rectangular plate and straight wires arranged in any fashion. Scattering by thin plates can also be solved. Electrical field integral equations of the Pocklington's type are formulated. These equations are solved by the Bubnov-Galerkin projective method with Lagrangian interpolation polynomials as basis functions. Numerical results are shown to give good agreement with those obtained by other methods.

DOI:10.1049/piee.1977.0080

出版商:IEE    

年代:1977

数据来源: IET

摘要:

A system is described which permits the automatic transcription of music from keyboard instruments. An electronic system is used to record online digital data from a keyboard and to provide transmission to a digital cassette recorder. Subsequently, the information stored on the cassette is processed offline to produce a transcription of the original keyboard performance in the format of conventional music notation.

DOI:10.1049/piee.1977.0081

出版商:IEE    

年代:1977

数据来源: IET

摘要:

A generalised mathematical method for the design of electronic function generators is developed by considering the relatively simple problem of generating precise sinewaves. The new approach enables many different waveforms to be generated in the same system, by only modifying it slightly. Most of the paper deals with the mathematical properties of the models of such systems. It is shown that the new oscillators possess a relatively large potential of performing accurately.

DOI:10.1049/piee.1977.0082

出版商:IEE    

年代:1977

数据来源: IET

DOI:10.1049/piee.1977.0084

出版商:IEE    

年代:1977

数据来源: IET

摘要:

The mechanism of resonance-induced maloperation of stepping motors is studied, and a simple analytical method is presented enabling resonance frequency bands, and the damping factors necessary to suppress resonance, to be predicted. Emphasis is placed on the determination of the equivalent linearised torque/displacement characteristic for practical use. Experimental results for the bands of resonance-induced maloperation of a 3-stack stator, variablereluctance type of motor confirm the approach. The occurrence of reverse running in a highly stable, double-speed mode at certain, nonresonant frequencies is reported and briefly commented on.

DOI:10.1049/piee.1977.0085

出版商:IEE    

年代:1977

数据来源: IET

摘要:

The paper describes a variable-voltage induction-motor fan drive, in which the rotor is constructed of hollow unlaminated steel and is cooled using the rotating-heat-pipe principle. A procedure for performance computations is presented, and the special properties of fan drives with unlaminated rotors are demonstrated by both theoretical and tested results for an experimental machine. It is shown that the design successfully overcomes the normal problem of fan-drive cooling in the region of slip equal to ⅓. Difficulties associated with losses at low slip are identified, and ways of relieving this problem are examined.

DOI:10.1049/piee.1977.0086

出版商:IEE    

年代:1977

数据来源: IET

摘要:

The paper presents a general theory of wave propagation through nonhomogeneous multiconductor systems. This theory shows that waves travelling in one direction through such a system do so independently of waves travelling in the opposite direction. The essential difference between homogeneous and nonhomogeneous systems is found to be that, in the former case, the propagation characteristics are the same in both directions, whereas in the latter case they are not. Methods for determining the forward and backward wave characteristics of a general nonhomogeous system are presented. The theory finds immediate application in the study of transient phenomena in powertransmission systems whenever nonhomogenity is involved. However, the theory is completely general, and may find useful applications in other areas.

DOI:10.1049/piee.1977.0088

出版商:IEE    

年代:1977

数据来源: IET

摘要:

A model of the high-voltage direct-current transmission link suitable for incorporation in fast decoupled a.c. load-flow programs is described. The model is not restricted to a particular control made and provision is made to alter the control equations according to prespecified constraints for the variables. The versatility of decoupled programs is increased with this addition and it is shown that their reliability and computational efficiency are maintained.

DOI:10.1049/piee.1977.0089

出版商:IEE    

年代:1977

数据来源: IET