Online ISSN
1350-911X
Print ISSN
0013-5194
Electronics Letters
Volume 6, Issue 17, 20 August 1970
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Volume 6, Issue 17
20 August 1970
Refraction and reflection of ultrasonic surface waves by thin-gold-film layers on lithium-niobate substrates
- Author(s): M.E. Pedinoff and M. Waldner
- Source: Electronics Letters, Volume 6, Issue 17, p. 533 –534
- DOI: 10.1049/el:19700370
- Type: Article
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Acoustic-surface-wave phenomena similar to optical refraction and total internal reflection have been observed in thin metal prisms deposited on y cut lithium niobate. In addition, scattering of the surface waves has been observed both at the boundaries and interior of the gold-film prisms. The observed total internal reflection and refraction angles were found to agree with theoretical predictions.
Spherical-harmonic expansions in near-field aerial problems
- Author(s): P.J. Wood
- Source: Electronics Letters, Volume 6, Issue 17, p. 535 –536
- DOI: 10.1049/el:19700371
- Type: Article
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The spherical-harmonic expansion may be applied to a certain class of near-field aerial problems. The conditions for validity of the expansion and the associated convergence problems are discussed.
A priori stability guarantee for suboptimal-control designs
- Author(s): D.H. Mee
- Source: Electronics Letters, Volume 6, Issue 17, p. 536 –538
- DOI: 10.1049/el:19700372
- Type: Article
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Control laws designed by minimising quadratic-performance indices with simplified linear dynamics may produce instabilities when applied to the actual plant. An a priori method of guaranteeing stability is derived using the known or approximated modelling errors.
Langmuir-probe measurement of electron temperature in a flowing high-density plasma
- Author(s): R.M. Clements and P.R. Smy
- Source: Electronics Letters, Volume 6, Issue 17, p. 538 –539
- DOI: 10.1049/el:19700373
- Type: Article
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Measurements with cooled double probes in a propane-air flame show that the measured electron temperature and the floating voltage of the probes can be strongly affected by variation of the probe temperature. Simple theoretical considerations indicate that these effects arise from cooling of the plasma electrons by collisions with cold molecules in the hydrodynamic boundary layer surrounding the probe.
Attenuation of dispersive Rayleigh waves on quartz
- Author(s): G. Cambon and M. Rouzeyre
- Source: Electronics Letters, Volume 6, Issue 17, p. 539 –541
- DOI: 10.1049/el:19700374
- Type: Article
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The attenuation properties of Rayleigh waves propagating in the x direction of y cut quartz have been measured with various metal films in the 30–157 MHz frequency range. The strong increase in the attenuation with film thickness is explained in terms of mechanical coupling and energy losses in the amorphous-metal films.
On Wu's theory of microstrip
- Author(s): P. Delogne
- Source: Electronics Letters, Volume 6, Issue 17, p. 541 –542
- DOI: 10.1049/el:19700375
- Type: Article
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An important error in Wu's 1957 paper on the theory of microstrip, leading to exponentially increasing fields, is corrected.
Adaptifon system for telephony — an alternative implementation of the Lincompex concept
- Author(s): J.A. Betts
- Source: Electronics Letters, Volume 6, Issue 17, p. 542 –543
- DOI: 10.1049/el:19700376
- Type: Article
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The compression and expansion circuits of the Lincompex system are each realised by using an adaptive delta modulator to perform an analogue-digital-analogue conversion. It is also shown that the Lincompex control signal giving information of the syllabic variations is readily available from the delta modulator.
Determination of the noise parameters of a linear 2-port
- Author(s): M.S. Gupta
- Source: Electronics Letters, Volume 6, Issue 17, p. 543 –544
- DOI: 10.1049/el:19700377
- Type: Article
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A new algorithm is given for the calculation of the four noise parameters of a linear 2-port from experimental measurements of its noise figure as a function of source admittance. A computer program for performing this calculation is briefly described (more detailed documentation is available).
Decreasing antenna beamwidth with increasing scan angle
- Author(s): R.C. Hansen
- Source: Electronics Letters, Volume 6, Issue 17, p. 544 –545
- DOI: 10.1049/el:19700378
- Type: Article
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All antennas, including phased arrays, exhibit beam broadening in the near field and also beam broadening in the far field at scan angles off broadside. For scan angles in the near field, the effective aperture is reduced, thereby producing less beam broadening due to the near field. At any scan angle, there is a near-field distance at which the broadside far-field beamwidth plus broadening equals the scan angle far-field beamwidth plus broadening. For larger scan angles, the beamwidth is less than at broadside. Calculations of this phenomenon are made for uniform linear and for tapered circular apertures.
Stopping conditions for iterative control-function optimisation
- Author(s): J.C. Allwright
- Source: Electronics Letters, Volume 6, Issue 17, p. 545 –547
- DOI: 10.1049/el:19700379
- Type: Article
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Iterative control-function optimisation for linear dynamical systems with quadratic performance indices is considered. Conditions are given which enable the stage to be determined at which the control function achieved is an adequate approximation to the optimal control function, with respect to the performance index. These yield useful stopping conditions. A computed example is presented.
Applicability of Kirchhoff integral to antenna near fields
- Author(s): J.R. James
- Source: Electronics Letters, Volume 6, Issue 17, p. 547 –549
- DOI: 10.1049/el:19700380
- Type: Article
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The physical interpretation and subsequent application of Silver's formula to aperture fields containing surface waves is questioned. Using the more general Kirchhoff and Weber integrals, it is shown that the choice of the complex radial wavenumber k1 in these formulas must be consistent with the radial field decay; the formulas are therefore not applicable to composite fields having components with different radial decays. An antenna with a composite near field is described and the implications are discussed.
Active filters and gain-bandwidth product
- Author(s): E.A. Faulkner and J.B. Grimbleby
- Source: Electronics Letters, Volume 6, Issue 17, p. 549 –550
- DOI: 10.1049/el:19700381
- Type: Article
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For several active-filter configurations employing operational amplifiers, the variation of resonance frequency and Q factor is given as a function of the ratio of the resonance frequency to the gain-bandwidth product of the operational amplifier. Consideration of these equations leads to the choice of the Wien-bridge filter or its equivalents for applications requiring a high Q factor at high frequencies.
Novel type of cut for KDP crystals for low-voltage light modulation
- Author(s): K. Hookabe and Y. Matsuo
- Source: Electronics Letters, Volume 6, Issue 17, p. 550 –551
- DOI: 10.1049/el:19700382
- Type: Article
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It is shown that a new type of cut of KDP, ADP and their isomorphs is useful for low-voltage operation of a light modulator.
Effect of various gases on formative times of laser-triggered spark gap
- Author(s): S.H. Khan and D. Walsh
- Source: Electronics Letters, Volume 6, Issue 17, p. 551 –553
- DOI: 10.1049/el:19700383
- Type: Article
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According to the streamer theory for the laser-triggered spark gap, gases with higher Townsend α coefficients and avalanche drift times. Thus faster switching was observed by using oxygen or air instead of nitrogen (in that order) or by increasing the amount of argon added to nitrogen. Clouding of the focusing lens was observed over a group of about 200 laser shots at 7 MW. No significant lens clouding was observed with 5 MW laser power, even after 1000 shots.
Radiation resistance of a square loop in a warm plasma
- Author(s): R.K. Gupta and I.L. Freeston
- Source: Electronics Letters, Volume 6, Issue 17, p. 553 –554
- DOI: 10.1049/el:19700384
- Type: Article
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A linearised hydrodynamic theory has been used to calculate the radiation resistance of a square-loop antenna in a warm plasma. It is suggested that cosinusoidal currents of two different propagation coefficients and amplitudes are simultaneously and independently present. Comparisons of the theoretical results with the measured values of the radiation resistance of a square-loop antenna on Ariel 3 satellite gives the ratio of the amplitudes of the currents in the two modes, for various values of the ratio of plasma to measuring frequency.
Evidence for a correlation between discontinuities and filamentary conduction in the forward characteristic of diode thyristors
- Author(s): I. Thomson and D.A. Vincent
- Source: Electronics Letters, Volume 6, Issue 17, p. 555 –556
- DOI: 10.1049/el:19700385
- Type: Article
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Evidence obtained from the effect of a magnetic field on the static characteristic of a diode thyristor indicates a correlation between discontinuities, or voltage shifts, and filamentary conduction. These results are consistent with the model which equates the discontinuity to a change from a filamentary to a uniformly conducting state.
Adaptive equaliser for multipath channels
- Author(s): R.T. Boyd and F.C. Monds
- Source: Electronics Letters, Volume 6, Issue 17, p. 556 –558
- DOI: 10.1049/el:19700386
- Type: Article
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An adaptive equalising system is described which makes possible efficient communication of serial digital data over a multipath channel, within certain limitations of the severity of the multipath. This technique is particularly suitable for two paths of comparable strength.
Electronic-network analysis by digital computer
- Author(s): W.R. Jackson and R.G. Sale
- Source: Electronics Letters, Volume 6, Issue 17, p. 558 –560
- DOI: 10.1049/el:19700387
- Type: Article
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The development of a program based on 2 × 2 matrices for computing the linear steady-state performance of networks against chosen frequencies of a sinusoidal input signal is described. Limitations and projected extensions of the program are briefly discussed.
Erratum: New equivalent circuits for elementary piezoelectric transducers
- Author(s): R. Krimholtz ; D.A. Leedom ; G.L. Matthaei
- Source: Electronics Letters, Volume 6, Issue 17, page: 560 –560
- DOI: 10.1049/el:19700388
- Type: Article
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Erratum: Dielectric Green's function for parameters of microstrip
- Author(s): J.A. Weiss and T.G. Bryant
- Source: Electronics Letters, Volume 6, Issue 17, page: 560 –560
- DOI: 10.1049/el:19700389
- Type: Article
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