摘要:

An approximate diffraction theory based on the Sommerfeld half-plane solution is developed. It is shown that, in certain regions, the electromagnetic field scattered (in the two-dimensional problem) by a perfectly conducting half-plane with plane waves incident can be conceived as arising from the flow of electric and magnetic currents along the edge of the half-plane. Thisedge-currentconcept is extended to the diffraction of normally incident plane waves by an aperture of arbitrary form in a thin, perfectly conducting screen of infinite extent.The approximation is for large apertures and is probably asymptotic. Interaction between the fields scattered by different parts of the screen is neglected in the present treatment.Expressions are obtained for the tangential electric field in the aperture in terms of these edge currents. The case of the circular aperture is studied in some detail, axial and aperture field distributions being derived and compared with the available experimental and theoretical data. Agreement with experiment and theory is fairly close, and improves with increase of the ratio of aperture radius to wavelength of incident radiation.

DOI:10.1049/pi-c.1956.0021

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The frequency spectrum of a 1/50 microsec impulse wave is obtained by the use of the Fourier transform. The corresponding frequency spectrum of the output from a simple capacitance potential divider, suitable for use up to 300 kV, is calculated from the input frequency spectrum for a 1/50 microsec wave and the frequency response of the divider, measured up to about 3 Mc/s. From this output frequency spectrum the output at a time of 1 microsec is calculated, and thus the divider ratio, suitable for peak-voltage measurements, is estimated. Consideration is given to errors due to the limited frequency range of the measurements, and the accuracy of the measurement of the divider ratio is estimated to be better than ±1%.

DOI:10.1049/pi-c.1956.0022

出版商:IEE    

年代:1956

数据来源: IET

摘要:

By way of introduction, the Wiener method of optimization of linear control systems with noisy inputs is briefly set out, and attention is called to the reasons why this method cannot be used directly for systems containing non-linear components. It is then shown that the difficulty with random inputs arises because the probability distribution of the output can be calculated only when that of the error signal is known; but in order to obtain this quantity the distribution of input and output must be combined. Thus it is not, in general, possible to obtain explicit expressions for either the error function or the output. If all the distributions were Gaussian, spectral densities could be used to obtain a solution of the problem, and this is the basis of Burt's approximation (not previously published), which is given in detail. Unfortunately, when the input of a non-linear component is Gaussian, the output will be non-Gaussian, but in some cases it is possible to make the necessary approximation.The mathematical justification for this approximation and for Booton's approximation is given in the Appendix. Booton's approximation consists in dividing the non-linear characteristic into a linear part and what he calls “the distortion factor.” The slope of the linear part is adjusted to give the best fit on a mean-square-error basis, and the distortion factor is then neglected.A method of obtaining an explicit solution to any required degree of accuracy by approximating to the non-linear characteristic by a number of linear domains is given in the Appendix.Finally, the possible use of topological methods to determine the stability of non-linear systems with random inputs is discussed, and it is shown that for useful control systems the phase-plane diagram of error for no input can almost certainly be used in the design of nonlinear systems, provided that the bounds of input and output and their derivatives can be determined.

DOI:10.1049/pi-c.1956.0023

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The main purpose of the paper is to stimulate thought concerning terminology, notation and exposition of some basic parts of information theory. The notation used here is intended to be simple, nearly self-explanatory, readable in words from left to right, and suggestive of new applications. Moreover, sufficient generality is preserved ensure that entropy can be interpreted without necessarily depending on the frequentist definition of probability (as a limiting frequency an infinite sequence of trials). Mention is made of some connections of the theory with inverse probability and with mathematical statistics in general.

DOI:10.1049/pi-c.1956.0024

出版商:IEE    

年代:1956

数据来源: IET

摘要:

Measurements of the attenuations produced by air-filled rectangular waveguides of nickel, mild steel, Mumetal, Radiometal and Rhometal have been made in the frequency range 9000–9675 Mc/s. The permeabilities of the materials have been determined from these measurements and a knowledge of the roughness and resistivity of each waveguide internal surface. The effects of temperature on the h.f. permeabilities have also been studied, and some qualitative results are included on the effect of superimposing a steady magnetic field on the h.f. one.

DOI:10.1049/pi-c.1956.0025

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The paper first digests existing information about 3rd-harmonic fields, mainly published previously in piecemeal fashion, and then adapts and extends it into modern form for use in symmetrical-component theory as applied to machines. This theory has provided the basis for a very successful 3:1 pole-changing machine which is described in another paper,8and the present paper includes a number of test results which verify that the theory of 3rd-harmonic fields given here is essentially sound.

DOI:10.1049/pi-c.1956.0026

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The paper deals with heat radiation characteristics of filament structures in the region of 2000° K, such as are used in transmitting valves. It shows how the effects of mutual heating between the individual elements may be calculated, and includes a set of universal curves which enable the results to be readily applied to structures of cylindrical form.

DOI:10.1049/pi-c.1956.0027

出版商:IEE    

年代:1956

数据来源: IET