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Electrical Engineers, Proceedings of the Institution of

Issue 2 • Date February 1964

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Displaying Results 1 - 25 of 43
  • Surface-wave resonance phenomena on dielectric tubes

    Page(s): 215 - 221
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (748 KB)  

    It has been shown theoretically that resonant azimuthal surface waves can be set up on a cylindrical-surface reactance sheet, and the special case of a line-source excitation has been studied by Cullen and by Wait and Conda. In the present paper the use of a dielectric tube to provide the necessary surface reactance is studied theoretically and experimentally. The main features of the theory are confirmed, but there are some discrepancies in detail which require further study. Possible applications are discussed, particularly in relation to the supergain-aerial problem. View full abstract»

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  • Guided waves in statistically random media

    Page(s): 222 - 230
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    A theoretical analysis of wave propagation in guiding structures with statistically varying parameters is given. The problem is treated as random cross-coupling among all the propagating modes of the structure, where the random functions describing the coupling coefficients are related to the inhomogeneities in the media or boundaries. It is shown that, in general, the solution is represented by a statistical quasimode which, in the mean, resembles the mode of the lowest attenuation, but that all the other coupled modes partake in a definite way in determining the nature of the mode. General formulas are derived which relate the properties of the solution to the statistical parameters. The use of the formulas is illustrated by application of the solution to a number of propagation problems. View full abstract»

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  • Hall-effect reinforcement of high-frequency fields in semiconductors

    Page(s): 231 - 234
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    The paper considers a number of high-frequency applications of a technique, described by Midgley, which uses Hall effect in a semiconductor to increase the penetration of an externally applied magnetic field. High-mobility semiconductors, like the intermetallic indium compounds, giving large Hall effects, also have a high conductivity with a correspondingly small skin depth, so that it becomes difficult to utilise the body of the semiconductor effectively. Hall-effect reinforcement of the applied field is therefore particularly valuable at high frequencies, and methods by which this may be exploited to advantage in Hall-effect and magnetoresistance-effect linear mixers, power-measuring devices and mode transducers, are discussed. A new form of electrically controlled attenuator embodying the same principle is also proposed. View full abstract»

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  • Wideband u.h.f. amplifier using earthed-grid triodes

    Page(s): 235 - 240
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    An untuned u.h.f. amplifier giving a mean gain of 25dB from 650 to 1000 Mc/s is described. Three discsealed triodes (type 416B) are cascaded in earthed-grid stages. Matching of interelectrode capacitances and the realisation of the broadband interstage transformers are obtained by simple transmission-line theory. The matching networks are constructed in slabline with a cylindrical inner conductor of a diameter suitable for axial mounting of the triodes. The noise figure varies from 7 to 10dB over the frequency band. Features of the design are the simplicity of the circuit configuration and the elimination of all tuning adjustments, with consequent ease of valve replacement. An extension of the circuit theory is briefly described, and it is shown that gain-bandwidth products in excess of the commonly accepted values can be achieved. View full abstract»

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  • Superheterodyne radiometers for short millimetre wavelengths

    Page(s): 241 - 256
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    Millimetre-wave radiometers suitable for making temperature measurements on plasmas are discussed. After a brief review of radiometer theory, special attention is paid to the design of the low-frequency radiometer circuits, the performance of mixer and harmonic-mixer crystals at short millimetre wavelengths, the local-oscillator power needed and the suppression of local-oscillator noise and spurious signals. An early 140-Gc/s radiometer, with second-harmonic mixing and an overall noise factor of 25dB, is mentioned, and a detailed description is then given of a recent 140Gc/s radiometer which contains: a fundamental local oscillator, VX3352 mixer crystals and a 408Mc/s i.f. amplifier commencing with an Adler tube. An overall noise factor of 19dB has been achieved with this equipment and its performance is fully discussed. Some typical recordings of the 2mm radiation from an argon noise tube and Zeta are included. Various ways of obtaining improved radiometer performance at millimetre wavelengths are mentioned. The appendixes are devoted to radiometer theory and an analysis of the halfwave commutator detector. View full abstract»

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  • Recent developments in silicon radar crystals

    Page(s): 257 - 263
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (710 KB)  

    Crystal valves have undergone considerable development in recent years, and much improved silicon detectors and mixers are now available. The improvements stem partly from a fuller understanding of semiconductor phenomena, partly from more rigorous design techniques, but largely from advances in materials technology, particularly with regard to the production of silicon tailored to meet specific requirements. With detectors, operation with maximum sensitivity over greater bandwidths has been the principal requirement. Progress in design is illustrated by reference to a range of experimental broadband crystals intended to cover frequencies from the lower end of the microwave spectrum up to 40Gc/s. These experimental types are being superseded by a new range of high-sensitivity detectors which operate with a small positive d.c. bias and give better stability and resistance to burnout and, moreover, are far easier to manufacture. Performance data are presented in some detail. Mixers have been improved in overall noise factor, particularly at Xband, and tighter control of their r.f. properties has been achieved. Compared with other semiconductors, silicon-type mixers are relatively insensitive to variations in local-oscillator drive power and resistance of the d.c. circuit or to temperature changes. The use of silicon proves particularly advantageous for low-flicker noise mixers, which are required in c.w. radars. Significant improvements in the conversion loss of mixers and in the sensitivity of detectors are becoming possible through the reduction of series-spreading resistance with crystals which use silicon films deposited epitaxially on to more highly conducting substrates. View full abstract»

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  • Characteristics of broadband parametric amplifiers using filter networks

    Page(s): 264 - 274
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    The paper gives a derivation of the relation between the bandwidth and the gain of a single diode parametric amplifier using filter networks at both signal and idling frequencies. Approximate algebraic expressions are obtained and compared with computed characteristics. The effects of small variations in component values are computed in an attempt to estimate the probable permissible tolerances for diode parameters and circuit elements. The phase- and group-delay characteristics are also computed, and the latter is shown to be of the order of twice the inverse of 2¿ times the amplifier bandwidth. The noise contribution due to the parametric action is shown to be a function of the signal frequency gain and the signal/idling frequency ratio. Because this relationship is such that the noise contribution falls with decreasing gain, the effective bandwidth of a low-noise receiver using a parametric amplifier as the first stage may be substantially greater than the normal bandwidth defined by a reduction of 3dB in the gain. Reported practical results are briefly examined in the light of the theory. View full abstract»

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  • Layer structure of the troposphere

    Page(s): 275 - 283
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    A discussion is presented of the manner in which layer-type echoes may arise and be observed using a 10cm radar at vertical incidence; such echoes are due to variations in the gaseous refractive index and not to water droplets in clouds or precipitation. Specular reflection and scattering processes are compared and the conditions indicated when an echo may be due to one or the other process, although the applicability of the turbulence theories used to relatively thin layers needs to be established. The results of the analysis are discussed in relation to data obtained from simultaneous soundings of the troposphere by radar and airborne microwave refractometers. Some comments are made regarding further experimental and theoretical investigations of the fine structure of elevated layers. View full abstract»

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  • Electronic system reliabilityߞan American viewpoint

    Page(s): 284 - 290
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    In the first part of this paper the economic aspects of system reliability are explored. The concept of the 'adequate system' is introduced, which system is defined as the lowest total-cost system that will perform as required. The relation of component-part cost to failure-rate levels is investigated, and the reactions of component performance upon design of an adequate system are examined in terms of the economic factors involved. A typical system is used to illustrate the points developed. Further, the number of systems needed to perform a given mission are considered in terms of annual cost and reliability levels of an individual system. The second part of the paper is concerned with the appraisal of the reliability of a system. This appraisal begins as early as possible in system evolution and makes use of estimation procedures which draw upon prior knowledge. Various assumptions which enter into such estimation methods are examined. It is pointed out that reliability estimates derived analytically must be verified by suitable tests of models at appropriate stages in the development of the system. The value of failure data obtained during the course of system development, manufacture and use in establishing levels of system reliability is emphasised. The final part of the paper deals with the effects of operating environment upon system reliability. The necessity of knowing the environment, and of conducting tests on models to evaluate its effects, is stressed. Two examples are given to illustrate some of the factors associated with environmental testing. One relates to the electrical performance of nickel-cadmium cells under space-simulation conditions; the other to the mechanical response of a structure under missile-flight environment. Broadly, the point of view taken is that electronic-system reliability is a synthesis of many related and interacting factors. Throughout the evolution of system design these factors should be most carefully balanced so that- - the ultimate product will perform at a level of reliability which is the optimum for the time, effort and money expended. View full abstract»

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  • Performance of an all-magnetic shift register

    Page(s): 291 - 302
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1606 KB)  

    The paper describes the characteristics and performance of the MAD-R shift register which uses multiapertures and connecting wire as the only components. In particular, it discusses the hold and prime operations and their effects on the performance of this shift register. A small modification adapts the basic shift register for bidirectional operation. View full abstract»

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  • Variable linear phase-shifting network

    Page(s): 303 - 307
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (465 KB)  

    A network is described enabling the variation of a linear phase characteristic by a single terminating resistor. The network is based on one form of Bode's variable equaliser, the theory of which is briefly presented. Design equations are developed for evaluating the elements of the network. It is shown that variation of the basic loss of the network provides another means of controlling the slope of the resulting phase characteristic. The starting point in the design procedure is the formulation of a realisable linear phase characteristic. This characteristic is realised by two constant-resistance bridged-T networks and an all-pass structure connected in cascade with a variable terminating resistor. Experimental results are given and close agreement with theory is demonstrated. View full abstract»

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  • Rotor windings for induction motors with arc-shaped stators

    Page(s): 315 - 321
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (900 KB)  

    Squirrel-cage induction motors in which the stator winding is limited to a fraction of the total periphery have performance inferior to conventional machines as the result of transient rotor currents set up by the edges of the energised arc. In particular, motors whose active zones contain only a few poles exhibit low efficiency, power factor and power/weight ratio. The paper describes a method of replacing the squirrel cage with a wound rotor which is short-circuited but which is so arranged that the undesirable transient effects at the two edges are made to cancel each other. The system is most favourable to cases in which the pole pitch of the machine is such that it divides evenly into the complete periphery. Results on an experimental machine indicate that the efficiency of a small machine, having only two poles in an energised arc of 120°, can be raised from just over 40% to over 80% by this technique, with correspondingly large increases in power output. The paper concludes with a brief discussion of the possible extension of the system to continuously variable-speed induction machines. View full abstract»

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  • Displacement governing in a 2-machine systemߝa hybrid simulator study

    Page(s): 325 - 334
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    The paper describes a study of the operation of displacement governors in the classical 2-machine system. A previous study of an isolated synchronous alternator with its prime mover controlled by this type of governor indicated that, with properly designed governor parameters, a great improvement in the dynamic-stability limit of the alternator could be effected. The object of this companion paper is to determine whether the optimised parameters of the isolated governed machine may still be employed and, if so, the effect on the system stability limits. Owing to the severe idealisation required to facilitate analytical treatment of this subject, the problem was studied on a power-system simulator, in which the alternator set and its prime mover were represented by a d.c. analogue, and the transmission system and load were represented by a l6kc/s network analyser, the two analogues being interconnected by coupling circuits. To provide some theoretical verification of this work, stability criteria have been developed by applying the Routh-Hurwitz stability criteria to the linearised equations of the idealised system. The work described clearly shows that an increase of 100% in the maximum load power that can be delivered in a 2-machine system may be achieved, provided that optimised gain-compensated governor stabilisers are used. View full abstract»

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  • Graphical method for solving transient stability problems

    Page(s): 335 - 342
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (643 KB)  

    A graphical method for solving transient power-system stability problems is presented. This method is especially simple and feasible for handling transient-stability problems of multimachines when damping is considered. Practical examples are presented to illustrate the applications of this method; tedious numerical computations are entirely eliminated, thus minimising arithmetical errors. The accuracy of this method is comparable to that of the analytical method. The allowable maximum input and effects of opening and reclosing a faulted line are considered in detail. View full abstract»

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  • Eddy-current losses in finite sections of solid iron under saturation

    Page(s): 343 - 348
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (679 KB)  

    The predetermination of eddy-current losses in solid iron due to an alternating magnetic field under saturation is a problem of great complexity. The problem is particularly difficult when the solid iron section is of finite dimensions. The object of the paper is to present a solution for the two-dimensional problem, taking into account the effect of saturation. The nonlinearity of the mean magnetisation curve is seen as producing a phase difference between the equivalent sinusoids of the magnetic intensity and the induction, in a way similar to hysteresis. This method of linearisation is carried out by introducing complex magnetic permeability, which obviously implies the substitution of the nonsinusoidal periodic functions of the magnetising force and the induction by equivalent sinusoids. The degree of saturation for any mean magnetisation curve is accounted for by the argument of the complex permeability. This concept leads to linearised differential Maxwell equations and provides a rigorous solution for losses in a two-dimensional problem. The analysis is applied to two different magnetic materials of finite sections and is verified against available experimental results. An interesting feature of the paper is that the results for the eddy-current losses are presented in a nondimensional form for extreme conditions of saturation. The table of computed results will be useful for a designer. View full abstract»

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  • Equivalent circuit of solid iron core for impact excitation problems

    Page(s): 349 - 357
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (994 KB)  

    In designing machines and apparatus with solid or partly solid magnetic circuits, it is necessary to predetermine the flux/time and current/time curves to obtain a desired rapidity of response. This requires precise knowledge of the damping action of eddy currents. Rigorous analysis of the problem for a core of rectangular section, taking into account the resistance of the magnetising winding, is difficult to obtain and has not been attempted so far in published work. The problem is all the more complicated when the nonlinearity of the material of the iron core is taken into consideration. The paper presents a method of reducing the solid iron core to a circuit analogous to that of a transformer with short-circuited secondary winding. The basis for obtaining the circuit is the eddy-current expression under alternating magnetisation for a solid iron core of large width/depth ratio, obtained from Maxwell equations. The equivalent circuit consists of secondary resistance and leakage reactance, which depend on the shape of the section and the electrical and magnetic characteristics of the material. The circuit obtained for constant permeability is then extended for use under nonlinear conditions. This method of obtaining the equivalent circuit results in an original treatment of the problem and gives an insight into the phenomena involved in the magnetisation of a core due to impact excitation. The results obtained from this theory compare favourably with test results. View full abstract»

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Aims & Scope

The Proceedings of the Institution of Electrical Engineers was published by the IET between 1963 and 1979.

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