摘要:

The well known definitions of guided and resonant modes (eigenfunctions) of a loss-free system are briefly examined and extensions to lossy systems are discussed.It is argued that the main advantage of the use of proper eigenfunctions lies in the fact that an arbitrary field in a homogeneous and closed waveguide system can be resolved into a spectrum of a complete set of orthonormal proper modes. This is a mathematical concept which is extremely useful in a wide variety of theoretical problems, because various well established and powerful analytical techniques can be used to advantage.It is shown that practical waveguide systems are neither closed nor homogeneous; the fields, therefore, extend to infinity and obey statistical laws. Consequently, in practical problems, serious mathematical difficulties are encountered, which, to some extent, can be circumvented by the introduction of continuous spectra that can frequently be identified with contributions to the radiation field or the scattered field.Furthermore, it is shown that, in all properly formulated physical problems, the discrete spectrum of proper eigenfunctions is absent and the complete solution is given by a continuous spectrum, which is usually interpreted as a radiation field. Yet, physical systems exhibiting distinct resonant or guiding characteristics are common, and it is concluded that such characteristics must be hidden in the continuous spectrum of proper eigenfunctions.It is shown that, in general, it is possible to transform the continuous spectrum into a spectrum of quasimodes (which are suitably chosen portions of improper eigenfunctions) and thereby obtain rapidly convergent field presentations which exhibit the physically observable resonance and guiding characteristics.The method is illustrated by application to a few examples.

DOI:10.1049/piee.1964.0294

出版商:IEE    

年代:1964

数据来源: IET

摘要:

This paper is concerned with the closed helical waveguide and deals mainly with the rotation of the planes of polarisation of waves passing through it.A theory is presented for electromagnetic propagation in a helical waveguide. The waveguide is divided into two regions: the groove space and the centre space. The regions are considered separately, and the dispersion equation obtained by matching the fields at the boundary between them. The characteristics of propagation in helical waveguides are discussed and propagation curves given for two helixes.Measurements have been made of wavelengths in the helix, and it is found that measured values are slightly smaller than calculated values.Investigation of the rotation of the plane of polarisation of a wave passing through the helix shows that, at frequencies approaching cutoff, the rotation is linear and between 60° and 80° per wavelength. At higher frequencies the rotation is 360° per pitch and is independent of wavelength. The former effect is shown to be caused by two modes in the helix interacting; the latter effect is caused by the interaction between space harmonics of a single mode.

DOI:10.1049/piee.1964.0295

出版商:IEE    

年代:1964

数据来源: IET

摘要:

By making use of the shift-and-add property of the maximal-length linear binary sequence, phase-delayed versions of the same sequence can be obtained by means of linear logic networks (modulo 2 adders) in conjunction with the sequence generator (e.g. a feedback shift register). This approach gives an alternative to the straightforward one which actually introduces the required time delays.The optimum way of deriving delayed versions in order to minimise the number of serial logical operations is indicated. The maximum number of serial additions required is given closely by log2n, wherendenotes the number of binary stages in the generator. The advantages and shortcomings of this approach are briefly discussed.

DOI:10.1049/piee.1964.0297

出版商:IEE    

年代:1964

数据来源: IET

摘要:

The paper presents tables which facilitate the design of low-pass and band-passRCactive filter networks having Cheby̅shev 2nd- and 4th-order response in both pass and stop bands.The synthesis method used is that due to Yanagisawa. This yields a network containing a current-reversing negative-impedance convertor and passiveRCnetworks to obtain a required voltage transfer function. An optimum polynomial due to Sipress is used in the synthesis, giving the minimum sensitivity of the filter response to errors in the transfer characteristic of the negative-impedance convertor.The design procedure using Zolatarev fractions is outlined, and the method for obtaining required amplitudes of ripple in the pass band is explained. The selection of certain ripple amplitudes requires a change in the network configuration.The Yanagisawa-synthesis procedure is discussed briefly, the use of the design tables is explained and an example is given. Experimental results obtained with 2nd- and 4th-order low-pass filters are shown and are compared with the theoretical curves.

DOI:10.1049/piee.1964.0298

出版商:IEE    

年代:1964

数据来源: IET

摘要:

A simple expression is derived for the focal length of the ring aperture of a toroidal hollow-beam gun. A digital-computer programme has been developed to determine the perveance from the potential, the electric field and the second derivative, with respect to toroidal radius, at the anode. With the expressions for the space-charge effect, the lens effect and the perveance, sets of design charts for possible gun parameters can be calculated. The outer electron-beam boundary is here defined by a parametern, which describes the required minimum beam cross-section; the inner beam boundary is determined by the fact that the electron trajectories behind the anode must be made parallel to the axis, as no space-charge force is acting on the electrons of the inner beam boundary.Several guns have been built to verify the calculations experimentally. When designed according to the above calculations, they produce very well defined electron beams. These beams have been analysed with a pinhole probe and a pinhole-sector probe which permits measurement of the direction of the current density. These results also verify the calculations given in a previous paper, concerning the space-charge flow between cathode and anode of a toroidal hollow-beam gun.

DOI:10.1049/piee.1964.0299

出版商:IEE    

年代:1964

数据来源: IET

摘要:

If a squirrel-cage induction motor is to be operated efficiently over a wide speed range, it must be supplied from a variable-frequency source whose frequency is adjustable over a range similar to that required for the motor speed. It is now technically possible and economically acceptable to provide power at variable frequency using silicon-controlled-rectifier (or thyristor) invertors. The paper reviews the already well known invertors and concludes that the d.c. link type is preferable for most variable-speed applications. Various methods of artificial commutation are described and applied to invertor circuitry suited to the supply of a squirrel-cage motor. The design flexibility of such an invertor is discussed with reference to component values and losses. Various methods of obtaining the necessary variable voltage are presented. Three different types of control circuits and their influence on drive characteristics are given. Finally, the characteristics of the invertor and motor forming a variable-speed drive are described, and applications are considered where speed, temperature, waterproofing and electrical maintenance are a limitation.

DOI:10.1049/piee.1964.0302

出版商:IEE    

年代:1964

数据来源: IET

摘要:

The distribution of magnetic flux in the air gap of an electric machine is of fundamental importance in determining such quantities as stray losses, torque, reactances and magnetic noise. The author discusses some of the methods of approach which have been employed in the determination of the basic flux quantities in induction and other doubly slotted machines. By a new form of analytical approach, equations are obtained for some important quantities; these include accurate, but simple, equations for gap permeance and the amplitude of certain flux pulsations. Also developed are some basic equations for air-gap leakage flux, including its variation with rotor movement. Tests made on models in an electric-tank analogue confirm the equations obtained for this component of leakage flux and give some additional information regarding flux pulsations.

DOI:10.1049/piee.1964.0303

出版商:IEE    

年代:1964

数据来源: IET

摘要:

This paper describes a type of double-layer winding known as an interspersed winding, which may be used in a.c. machines to reduce harmonic components of induced e.m.f. or load m.m.f. The principles underlying the design of interspersed windings are described and compared with the standard analysis of conventional windings in terms of harmonic winding factors. Design and performance details are then given for a complete range of 3-phase interspersed windings covering equivalent values of slots/pole per phase from 4 to 9. It is shown that control of the largest low-order harmonics may be achieved with insignificant alteration to manufacturing methods, and this type of winding should therefore find useful application in large generators and motors where the reduction of stray load losses is an important consideration.

DOI:10.1049/piee.1964.0304

出版商:IEE    

年代:1964

数据来源: IET

摘要:

A theory of stability for nonlinear feedback systems interfered with by an external periodic signal is developed. It makes use of a conventional dual-input describing function which may be available in an analytic or graphical form. The interference may take a variety of forms: the external signal may be injected into the loop, modulate the loop gain or vary any other parameter of the system, or it may interfere in a combination of the above ways. The nonlinearity may be analytic or discontinuous but it must be independent of frequency.A simple servomechanism with backlash and an injected sinusoidal signal is studied, and oscillations at frequencies subharmonic to that of the signal are examined.The stability of a self-optimising control system with sinusoidal perturbation of one parameter is examined. Symmetrical and asymmetrical criterion curves are considered. Second- and third-subharmonic oscillations are found possible: in some circumstances they are stable and self-starting; in others they are unstable, in which case external excitation may cause their onset.The systems were simulated, and experimental results were found to agree well with the theory.

DOI:10.1049/piee.1964.0311

出版商:IEE    

年代:1964

数据来源: IET

摘要:

The paper considers the behaviour of model-reference adaptive control systems when the system is very simple. Theoretical analysis of the behaviour of the adaptive loop is followed by analogue-computer studies. A second-order system with a second-order model and then a third-order system with a second-order model are considered. Effects of various inputs are investigated, including a ramp, square wave and white noise.The results demonstrate that the model-reference adaptive loop is capable of very fast response. It is also shown that, where the system and the model are of a different order, the frequency spectrum of the input has to be carefully considered to avoid large errors. It is also shown that one effect of the presence of noise may be to keep the loop parameters at or around their correct value in the absence of demand signal.

DOI:10.1049/piee.1964.0312

出版商:IEE    

年代:1964

数据来源: IET