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Electrical Engineers, Proceedings of the Institution of

Issue 2 • Date February 1971

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Displaying Results 1 - 24 of 24
  • Influence of directional fluctuations on the gain of horizontal rhombic aerials for high frequencies

    Page(s): 281 - 286
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    The response of a horizontal rhombic aerial to waves which fluctuate in direction of arrival is considered, and numerical values of the gain degradation from this cause are given for a wide range of practical aerial and wave parameters. Experimental data on the directional variations associated with single modes of propagation at long ranges are briefly reviewed, and it is concluded that such variations do not constitute any limitation in practice on the size of rhombic aerials for high-frequency communication. View full abstract»

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  • Modes in a conical horn: new approach

    Page(s): 287 - 292
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    An analytically simple, sufficiently accurate, and self-consistent solution for modes in a conical horn is presented. The eigenfunctions and eigenvalues derived from the simpler solution for the TE and TM modes of different orders are close to the exact solution. Application of the simpler solution for obtaining the aperture field and, subsequently, the far-field-radiation patterns of conical horns of arbitrary flare angles excited in the TE11 mode, with the aid of a vector diffraction formula, yields results in close agreement with experiment. The new approach provides a simple and accurate solution for the balanced hybrid modes in corrugated conical horns with small and wide flare angles, emphasising the more general validity of the technique adopted. View full abstract»

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  • Radar antenna with near-field cylindrical obstruction. Computer-program description

    Page(s): 293 - 300
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (803 KB)  

    A technique for the calculation of the radiation patterns of radar antennas with single near-field cylindrical obstructions is described. The computed and measured results are compared for a highly directional S band-radar antenna. Consideration is then given to the possible extensions of the method for cylinders of finite length and of noncircular cross-section, as well as for 3-dimensional radars. View full abstract»

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  • Diffraction by a conducting wedge in the near field

    Page(s): 301 - 304
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (426 KB)  

    The purpose of this paper is to derive a near-field asymptotic solution for the diffraction of waves by a perfectly conducting wedge. Thus, starting from the series solution for cylindrical-wave incidence and using an integral expression for products of the Bessel functions involved, the total field is represented as a geometrical-optics term plus a diffraction integral. Using an integral form for the field of a spherical wave, the solution for the cylindrical-wave excitation is extended to the spherical-wave case. The method of steepest descent is used to obtain an asymptotic expression for the diffraction integral in terms of Fresnel integrals. The accuracy of our expressions is established by comparison with previous results as well as the exact solutions. View full abstract»

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  • Equivalent electrical circuits of interdigital transducers for piezoelectric generation and detection of Rayleigh waves

    Page(s): 305 - 310
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (786 KB)  

    Experimental and theoretical studies of the generation and detection of Rayleigh waves by arrays of interdigital electrodes deposited on piezoelectric ceramics are described. Experiments with transient voltages suggest that such a transducer can be represented by a 1-dimensional equivalent electrical circuit based on that conventionally used for a bulk-wave transducer, incorporating tranmission lines and piezoelectric transformers. More detailed studies lead to the adoption of a model in which each electrode is represented by the ciruit of a bulk-wave transducer of width one-third of the spatial period of the array. This circuit is used in studies of three important characteristics: the continuous-wave radiation resistance of an array, the continuous-wave voltage transfer from a generating array to a detecting array, and the detector waveform resulting from a transient generating voltage. The circuit is shown to be capable of dealing simultaneously with all three situations more accurately than circuits previously proposed. View full abstract»

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  • Discrete-time systems with interwoven transfers

    Page(s): 312 - 316
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (471 KB)  

    Filters with capacitances, switches and regenerating devices constitute a class of periodically time-varying filters which can be analysed and synthetised using the pulse formalism developed by Fettweis. The paper offers a new interpretation of these filters as digital filters; the mechanism of the exchange of charge between capacitances, with and without regenerating devices, is analysed with the flowgraph technique, and the pulse transfer function of the filter is obtained. View full abstract»

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  • Gate tolerances in sequential circuits

    Page(s): 317 - 320
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (387 KB)  

    Maximum gate tolerances in sequential circuits are shown to be a direct function of the delays associated with the primary and secondary signals in critical races. Steps for allowing a gate-speed tolerance of up to ±33¿% to be accommodated in minimal designs are introduced. View full abstract»

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  • Fan-in restrictions in logic circuits

    Page(s): 321 - 327
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (650 KB)  

    Gate fan-in restrictions in logic circuits can be met at the design level by controlling the size of the sums and products of the corresponding Boolean expressions. A single-step procedure for meeting gate fan-in restrictions by limiting the size of the Boolean sums and products while retaining gate minimality is described. The steps are chosen to allow both hand and computer execution. View full abstract»

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  • Pathfinding in communication nets

    Page(s): 328 - 334
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (921 KB)  

    A routine is presented for determining the number and the set of all paths in oriented and in nonoriented communication nets. Duplication and the generation of nonpaths are mechanically prevented from occurring en route. The technique generalises to pathfinding in arbitrary nets. View full abstract»

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  • Speech-volume measurements on telephone circuits

    Page(s): 335 - 338
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (686 KB)  

    Knowledge of the electrical levels of speech signals at the input to speech-transmission systems is required for (a) study of the talking behaviour in telephone conversations (b) provision, from measurements under service conditions in the field, of basic data for estimating the power loading of multiplex transmission systems. For these purposes, an instrument has been designed which measures the r.m.s. voltage of the signal when integrated over a given period of several seconds. To cater for fragmentary speech, the total integration period is not fixed, the timing being stopped during silent periods. The period of `active¿ speech over which integration takes place is 10s. Accurate square-law integration over a sufficiently wide range of amplitude caters for the dynamic range of speech from a talker under conversation conditions. The operate and release levels, and operate and hangover times, of the timer switch have been chosen so that timing is not stopped during structural pauses, but only when a listener would have judged that the talker had stopped. Calibration is in decibels relative to 1V (dB V), and so conversion to decibels relative to 1mW (dBm) into an impedance of 600¿ requires the addition of 2.2dB to each reading. With this allowance, the reading may be regarded as `the long-term mean power while the talker is active¿. The instrument has been used to measure the distribution of speech volumes at the input to a transatlantic cable system and to make an estimate of the activity factor of the conversational speech so measured. View full abstract»

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  • Distortion effects in switching-diode modulators arising from local-oscillator interference

    Page(s): 339 - 342
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (509 KB)  

    The paper considers the situation of a switching-diode modulator driven by a local-oscillator signal derived from some source, typically a frequency synthetiser whose output contains both a significant level of random noise and also harmonically unrelated spurious tones at low level. The interaction of input signals to the modulator with the local-oscillator interference is considered, and expressions are derived for the output-signal levels arising from this interaction in terms of the local-oscillator signal/noise ratio. The performance is shown to be independent of local-oscillator source resistance and diode `offset¿ voltage. The performances of experimental Shottky-barrier modulators agree well with predictions. View full abstract»

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  • Self-calibrating grid attenuator for use at submillimetre wavelengths

    Page(s): 343 - 348
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (772 KB)  

    The theory and experimental results of a symmetric self-calibrating attenuator which consists of a rotatable grid situated between two fixed grids is presented. The attenuator is shown to have a cosine4 power-law variation at a frequency of 890.8 GHz. View full abstract»

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  • Optimised design of linear-induction-motor accelerators

    Page(s): 349 - 355
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (741 KB)  

    Linear-induction-motor accelerators may be designed to have continually changing field speeds so as to escape the penalties of a limiting efficiency of 50% to which fixed-field-speed accelerators are subject. The paper outlines a method of design for an accelerated-field system in which it is desired to reduce the overall length to a minimum, assuming a limit on the amount of heat which can be generated in the secondary member. The paper then shows that a primary unit designed to give several discrete field speeds only, as opposed to one with continuous speed variation, is not significantly inferior in performance to the latter but is much easier to manufacture. View full abstract»

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  • Stability of reluctance machines

    Page(s): 356 - 369
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2066 KB)  

    An experimental and theoretical study of rotor oscillations in reluctance machines, with particular reference to variable-frequency systems, is described. Measured performance characteristics, both steady-state and transient, are used to indicate the basic features of the oscillation and to confirm the validity of theoretically derived results. Machine sine-wave and invertor quasisquare voltage supplies are considered. Theoretical results are presented which bring out all the significant influences on the stability performance of reluctance machines. These lead to a much improved understanding of observed behaviour of actual machines, and indicate those directions in which improved performance may be achieved. The direct-axis-rotor-resistance/quadrature-axis-rotor-resistance ratio is shown to be particularly important in this respect. The theoretical results are obtained from the characteristic equation of the machine using the method of D decomposition, previously developed in a powerful form for the treatment of multiparameter systems, and permitting the derivation of the natural frequency and damping factor. The frequency of rotor oscillation increases progressively with supply frequency, but, in most practical circumstances, lies somewhere in the range 0.03¿0.15 p.u., the supply frequency then being in the range 0.1¿0.4 p.u. Brief consideration of the relationship between the reluctance-machine instability and that occurring in induction machines is included. View full abstract»

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  • Return-difference matrix properties for optimal stationary Kalman-Bucy filter

    Page(s): 373 - 376
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (425 KB)  

    A strikingly simple characterisation of the optimal stationary Kalman-Bucy filter is obtained in terms of the return-difference matrix for the associated feedback system. The spectral factorisation of the observation spectral-density matrix is shown to generate directly the appropriate return-difference matrix. This leads to a physical interpretation of the mechanism by which signal and noise are separated, which could form the basis of an approach to filter design. View full abstract»

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  • Optimal control of nonlinear stochastic systems

    Page(s): 377 - 380
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (557 KB)  

    The paper is concerned with the development of algorithms for near-optimal control of nonlinear stochastic systems with noisy-state observations. It is assumed that the control signal acts linearly on the plant and is a function of the output. The noise processes involved in the state and observation equations are taken to be independent and white-Gaussian processes. The index of optimisation is selected to be the minimisation of the variance of the error of control. Two 2nd-order approximations to the optimal solution are derived on the basis of recently established results. View full abstract»

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  • Constriction-resistance concept applied to wear measurement of metal-cutting tools

    Page(s): 381 - 386
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    The paper describes a mathematical model for the tool-workpiece-interface resistance in a single-point oblique-cutting operation on a lathe. The model is developed using the concept of constriction resistance, and is verified by practical measurements of the interface resistance. The measurement technique is important, and details are given of the significant factors. It is shown that the resistance measurements may be used to calculate the amount of wear on the cutting tool as cutting proceeds. Results show that this method gives the mean value of the flank wear-land width to within ±0.002 in (±0.05 mm) of independent optical measurements for a range of cutting conditions typical of finish-turning operations. View full abstract»

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  • Electric strength of transformer oil for large electrode areas

    Page(s): 388 - 393
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (710 KB)  

    Carefully controlled measurements of the electric strength of transformer oil are reported. Electrodes of large-diameter cylindrical geometry are used to obtain substantially uniform fields with an electrode area of up to 2m2. The results indicate the important influence of oil volume on the electric strength both for supply-frequency and 1/50¿s-impulse voltages. The effects of temperature, forced oil motion and the nature of gas in solution are also studied, and it is concluded that the oil flow is an important parameter in determining the statistical distribution of breakdown measurements. The test results have been explained on the basis of gas-initiated breakdown. 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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