摘要:

An analytic method for the reconstruction of the profiles of refractive indexes of inhomogeneous, stratified regions is presented. The reflection coefficientr(k) for time-harmonic electromagnetic waves is represented as a rational function ofk, the wave number. 1-dimensional inverse scattering theory has been applied to obtain analytic, closed-form expressions for the profile functionsq(x) fromr(k). The profile reconstruction method is demonstrated with a 3-poler(k), that results in aq(x) which resembles an ionospheric electron-density profile previously analysed by direct scattering methods. The present communication generalises previous results to oblique incidence and compares several.q(x) obtained from different rational approximations tor(k).

DOI:10.1049/piee.1979.0175

出版商:IEE    

年代:1979

数据来源: IET

摘要:

This paper reviews the experimental measurement of crosspolarisation on satellite-earth paths, describes the identification of previously unexpected depolarisation by ice crystals, and outlines the theoretical explanations of ice depolarisation which have been reported in the literature. It summarises what is known, and what is not yet understood, about ice-crystal depolarisation. The paper discusses the implications of ice-crystal depolarisation for satellite communications system design.

DOI:10.1049/piee.1979.0176

出版商:IEE    

年代:1979

数据来源: IET

摘要:

Using a finite-field transform, a simplified algorithm for decoding Reed-Solomon codes is developed to correct erasures as well as errors over the finite-fieldGF(qm), whereqis a prime andmis an integer. If the finite-field transform is a fast transform, this decoder can be faster and simpler than a decoder that uses more conventional methods.

DOI:10.1049/piee.1979.0177

出版商:IEE    

年代:1979

数据来源: IET

摘要:

Synthetic interruption test methods for a high-direct-current circuit breaker are investigated. The test method, which adopted a capacitor bank for a voltage supply, was recognised to be equivalent to a practical system. Finally, with this test method, a d.c. circuit breaker with vacuum interrupters was tested up to 130 kA/44 kV.

DOI:10.1049/piee.1979.0178

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The paper examines the validity of the theory arrived at by some authors, notably Alger, that the airgap leakage reactance of a polyphase squirrel-cage induction motor consists of two separate entities, namely, the ‘zig-zag’ reactance and ‘belt’ leakage reactance. The paper shows that not only the lower-order primary airgap m.m.f. harmonics have equal and opposing m.m.f.s induced in the secondary, but also the stator harmonics of pole-pair pitch smaller than the rotor slot pitch, which Alger calls ‘zig-zag’ leakage harmonics. This fact thus disproves that the ‘zig-zag’ leakage is a separate entity from the so-called ‘belt leakage reactance’, which Alger suggests should be disregarded for squirrel-cage motors. Further analysis reveals that the alternative theory of ‘differential leakage reactance’, as also derived by Alger, but on the assumption of vanishingly narrow slot-openings, is also valid for slot-opening which are not so. This, provided that the magnetising reactance, (with which the differential leakage coefficient must be multiplied to obtain the differential leakage reactance) incorporates the Carter airgap coefficient, as in fact it does in practice. The effect of slot-openings which are not infinitesimally narrow on the mean permeance and the permeance harmonics produced are also dealt with. The theory set forth in this paper is supported by locked-rotor tests on a number of machines.machines.

DOI:10.1049/piee.1979.0179

出版商:IEE    

年代:1979

数据来源: IET

摘要:

A frequency-domain approach for the transient modelling of a voltage-fed, double-sided sheet-secondary-type linear induction motor (l.i.m.) is discussed. The problem of sudden reconnection of the l.i.m. in the motoring and braking modes at different operating speeds is analysed using discrete Fourier transforms. Attention is focused on the transient currents and thrust pulsations immediately following the switching action. The computational considerations for efficient calculation of the time response of the machine are discussed. Experimental results pertaining to the switching-in of a 2.5 kW l.i.m. from a 3-phase supply are presented, and compared with the predicted theoretical results.

DOI:10.1049/piee.1979.0180

出版商:IEE    

年代:1979

数据来源: IET

摘要:

A method for designing stabilisers for high-speed static exciters which includes the systems nonlinearities and allows for nonlinearities in the stabilisers is presented. The method combines the use of nonlinear-optimal-control techniques and system-identification techniques to design flexibly structured stabilisers based on readily available outputs of the system. The method also allows the combination of information from many operating conditions in the design process. The performance of the method is first examined on a computer simulation of a single- machine/infinite-bus system. Then the method is tested on a microalternator system to verify the computer results and to demonstrate the practical feasibility of the design method. The results show that the stabiliser performs very well both for small changes in the reference inputs and large disturbance faults applied to the system.

DOI:10.1049/piee.1979.0181

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The basis and details are given of an accelerated lifetime-test procedure for assessing connectors on aluminium conductors. This test is designed to reproduce the degradation over the service lifetime, and the failure criterion is based upon the resistance values which would lead to failure in service. A large number of connectors can be tested, and this is shown to be essential if a reasonable degree of statistical significance is required in any test result. Results obtained from the new test are compared with those from a series of long-term current-cycling experiments chosen to reproduce a very arduous thermal history.

DOI:10.1049/piee.1979.0182

出版商:IEE    

年代:1979

数据来源: IET

摘要:

A general computer program using the phase co-ordinate technique has been developed for analysing series, shunt and simultaneous faults on balanced and unbalanced polyphase electrical networks. The program eliminates the need for maintaining numerous fault analysing subroutines, one for each kind of fault, and makes the solution of many difficult and previously unsolvable problems possible. It is employed to analyse the cross-country fault involving different phases. The solution method, program outlines and postfault results of voltages, currents and apparent power of an actual power system are given.

DOI:10.1049/piee.1979.0183

出版商:IEE    

年代:1979

数据来源: IET

摘要:

One of the major drawbacks to the use of gradient algorithms for the design of output-feedback controllers is the possibility of closed-loop instability following a step in the gain-parameter space. An algorithm is proposed which obtains optimal stepsizes at each stage of a gradient search, and automatically tests for and avoids unstable values of the gain parameters.

DOI:10.1049/piee.1979.0185

出版商:IEE    

年代:1979

数据来源: IET