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Popular Articles (February 2015)

Includes the top 50 most frequently downloaded documents for this publication according to the most recent monthly usage statistics.
  • 1. A review of automatic gain control theory

    Publication Year: 1981 , Page(s): 579 - 590
    Cited by:  Papers (16)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1163 KB)  

    The paper presents the general theory of automatic gain control (a.g.c). It includes discussions on loop gain, regulation and the relation between loop parameters and output level stability. An equivalent circuit is derived which is used in the study of dynamic behaviour. The work is extended to cover sampled data a.g.c. systems and design guidelines are derived for a variety of situations. View full abstract»

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  • 2. Coherent and non-coherent demodulation of envelope-modulated radio signals. With particular reference to the enhanced-carrier system

    Publication Year: 1963 , Page(s): 65 - 71
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (765 KB)  

    The ordinary ¿linear detector¿ and the coherent demodulator are briefly discussed as the two extreme cases of demodulators for envelopemodulated signals, since in the former the rectifier (or modulator) is switched by the complete input signal, while in the latter a pure local reference tone is used. The synchrodyne and enhanced-carrier systems are regarded as intermediate cases in which the switching is effected by an impure carrier derived from the incoming signal. The enhanced-carrier system, using filters to extract the carrier from the incoming signal, appears to have received little attention in the literature; and the distortion caused by tuning errors in the enhanced-carrier path and the interference due to unwanted input signas are here particularly considered. View full abstract»

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  • 3. Engineering approach to the design of tapered dielectric-rod and horn antennas

    Publication Year: 1972 , Page(s): 251 - 259
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1203 KB)  

    The taper profile of optimized dielectric-rod and horn antennas is synthesized as a series of non-interacting planar radiating apertures. The method is semi-empirical, straightforward to apply, enables the dielectric-rod antenna to be satisfactorily optimized and provides a means of evaluating and optimizing a dielectric-horn antenna with variable wall thickness. The optimum profiles are taken as those which smoothly transform the surface-wave power from the launcher to the radiating aperture. The optimization of the dielectric-rod antenna considerably improves the radiation pattern while computations supported by measurements confirm earlier reports that a dielectric-horn can have a higher gain than a metal horn of similar dimension but side-lobe level is seen to be an important issue. Wide flare-angle horns give ideal E-plane patterns at the expense of a high side-lobe level in the H-plane; for small flare angles the dielectric horn gives similar patterns to the tapered rod antenna and thus preserves rotational symmetry. Calculations throughout are restricted to cylindrical geometry but other geometries and variations on the dielectric-horn principles are described. Useful engineering design data have been compiled for both the dielectric-horn and rod antennas and curves are given which determine near-optimum parameters for gains up to about 20 dB which is seen to be a practical operating limit for these surface wave devices. A unified impression of dielectric antennas emerges with the important conclusion that, when optimized, dielectric-rod and horn antennas are in fact competitive with small metal horns for some applications; furthermore the dielectric-horn antenna, used singly or in arrays, is an ideal device for producing a low side-lobe level in the E-plane. View full abstract»

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  • 4. Amplitude performance of Ruze and Rotman lenses

    Publication Year: 1983 , Page(s): 329 - 336
    Cited by:  Papers (13)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1363 KB)  

    Ruze and Rotman lenses are devices which can be used to form multiple beams for antenna arrays. A previous paper has shown these lenses can be designed for low-phase aberrations and minimum size. Published work on these lenses has concentrated on phase and largely neglected amplitude performance (except Maybell). Here, a theoretical model is developed which predicts the primary amplitude distribution across the array ports of the lens; this then allows predictions of insertion loss and sidelobe levels of the fed array. An experimental waveguide-fed parallel-plate lens has constructed, and amplitude and phase performance measured. Comparison with the theoretical predictions shows good agreement. The multiple beam radiation patterns produced by a 16-element array fed by this lens have also been measured. The lens has a low insertion loss (¿2 dB) and provides a low sidelobe level (¿20 dB) for the 8¿12 GHz band. View full abstract»

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  • 5. The early history of amplitude modulation, sidebands and frequency-division-multiplex

    Publication Year: 1971 , Page(s): 43 - 47
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (742 KB)  

    It is shown that the ideas of f.d.m. originated with Alexander Graham Bell around 1870 and were formulated as an f.d.m. telephone system by Leblanc in 1886. Amplitude modulation of a carrier by speech probably originated also with Leblanc in 1886. The existence of sidebands (or sidetones) was demonstrated experimentally by Mayer in 1875 and theoretically by Rayleigh in 1894, but was not known to the early radio and telephone engineers, being apparently rediscovered in 1915. The main developments up to about 1920 are briefly discussed. View full abstract»

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  • 6. The practical design of interdigital and comb-line filters

    Publication Year: 1967 , Page(s): 39 - 52
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1398 KB)  

    The design procedures for interdigital and comb-line filters are summarized and the theory of these filters extended to include various aspects of design and performance which are not covered in the literature. The basic design equations are modified to give unified sets of expressions relating the resonator capacitances directly to the filter specification, and the theory of these filters is extended to include group delay, high-power breakdown effects and precise centre-frequency synthesis. In addition, the factors contributing to in-band dissipation loss are considered, and a method of predicting this loss in terms of the unloaded-Q of a slab-line resonator is given. Finally, a method of suppressing unwanted harmonic responses is outlined. View full abstract»

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  • 7. Design of stepped microstrip components

    Publication Year: 1978 , Page(s): 53 - 63
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1042 KB)  

    The analysis of the impedance step by the mode matching procedure using a waveguide model for the microstrip line yields an explicit design formula for the frequency-dependent equivalent series inductance. The single-section quarter-wavelength transformer is calculated under the assumption of interacting steps. It turns out that in regard to practical design the neighbouring steps can be considered to be decoupled so that the calculation can be done simply with the results given before. Finally the derived results for the impedance step are used to calculate the scattering matrix of an n-section tapered transmission line. Experimental data show good agreement with theory. View full abstract»

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  • 8. A novel ferrite quarter-wave plate

    Publication Year: 1964 , Page(s): 455 - 458
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (358 KB)  

    Coupled-wave theory is applied to make an adjustment to the length of an elliptical Faraday rotator to obtain a ferrite quarter-wave plate with non-reciprocal properties. A ferrite rotator can be interposed between two such quarter-wave plates and matrix algebra used to obtain a new reciprocal ferrite phase shifter. A pulsed 180 deg non-reciprocal phase shifter is also described. View full abstract»

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  • 9. Systems Engineering: an approach to whole-system design

    Publication Year: 1980 , Page(s): 545 - 558
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1715 KB)  

    Since World War II the magnitude and complexity of technological enterprise has increased dramatically. So too have the costs of development, mistakes and failures. The old-style project engineer who could often be his own designer and project manager has been replaced by a team¿the systems engineering staff¿who integrate, co-ordinate and evaluate the realization of a project through all its evolutionary phases. In particular, systems engineering has produced an approach to design and project appraisal that integrates and balances the various technical, economic, reliability, safety, logistic, support criteria oriented towards future market and operational requirements evaluated over the whole-life of the system. This introductory paper provides an entry to the systems concepts that underlie systems engineering, and then illuminates the practice through the perspectives of systems organization, design and planning. View full abstract»

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  • 10. A new analysis of the transistor phase-shift oscillator

    Publication Year: 1963 , Page(s): 145 - 153
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (613 KB)  

    The relationship between transistor parameters and circuit characteristics of an RC phase-shift oscillator is analysed by flow-graph and root-locus techniques. Exact formulae and approximations for the starting frequencies of three- and four-section RC phase-shift oscillators are derived. Prediction of the operating frequency for a given current gain is presented graphically and compared with experimental results. View full abstract»

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  • 11. Sources of intermodulation in diode-ring mixers

    Publication Year: 1976 , Page(s): 247 - 255
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1015 KB)  

    Intermodulation is known to arise in diode-ring mixers due to non-linearity in the diode switches, and also due to the interference by signal voltages with the local-oscillator switching function. This interference can be reduced by ensuring fast switching with a square-wave local-oscillator. In this paper the relationship between rise-time and intermodulation is investigated in connection with a practical mixer design for use at v.h.f. View full abstract»

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  • 12. The history of positive feedback: The oscillating audion, the regenerative receiver, and other applications up to around 1923

    Publication Year: 1972 , Page(s): 69 - 80
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2462 KB)  

    Positive feedback, or regeneration, played an important part in radio engineering during the two or three decades following its development for electronic circuits around 1912¿15. This paper reviews the earlier history of the subject, considers the controversial inventions of 1912¿15 in some detail, and goes on to examine some other applications of positive feedback in self-oscillating detectors, e.g. the autodyne, the homodyne and the super-regenerative receivers. View full abstract»

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  • 13. Recent trends and future developments in radar displays

    Publication Year: 1963 , Page(s): 459 - 467
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1285 KB)  

    The paper starts with a brief recapitulation of the development of radar displays, from the simple form of moving coil plan position indicator (p.p.i.) to the development of the d.c.-coupled fixed-coil displays, capable of allowing for target marking during intertrace periods. An extension of this technique uses secondary high-speed deflection coils to provide alpha-numeric identification of the intertrace position. A description is given of a modern transistorized radar display, capable of performing the dual role of raw marked radar display or synthetic display. Improvements in cathode-ray tubes, and the need for the bright display is discussed. Particular emphasis is given to the bright direct-view storage tube, and the method of operation and performance of displays using these tubes is given. Radar to television scan conversion systems are described in both forms, using either the bombardment induced conductivity tube, or the storage vidicon. Some comments are made upon the possible use of new devices such as electroluminescent panels. View full abstract»

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  • 14. Accurate analytical determination of quasi-static microstrip line parameters

    Publication Year: 1976 , Page(s): 360 - 364
    Cited by:  Papers (10)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (531 KB)  

    In the design of microstrip components, the analytical equations of Wheeler have an advantage in handling-speed and simplicity over alternative quasi-static analyses involving complex computation by numerical methods. Wheeler equations can produce excessive errors, however, unless care is taken particularly in the choice of changeover point between equations for narrow or wide strips. This paper shows that for alumina-type substrates with 8 < ¿r < 12, the Wheeler analysis and synthesis equations produce results within 1% of those given by selected numerical methods, when the changeover points are correctly chosen. Additional new and modified formulae are presented for the direct calculation of microstrip effective permittivity from either W/h or Z0, also to an absolute accuracy of less than 1%. These complete an accurate set of analytical equations for quasi-static analysis or synthesis of microstrip lines. View full abstract»

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  • 15. Operations on delta-modulated signals and their application in the realization of digital filters

    Publication Year: 1978 , Page(s): 431 - 438
    Cited by:  Papers (16)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    A new method is proposed with which it is possible to find a delta-modulated signal of the half sum of two analogue signals through a direct operation on their delta-modulated form. With a direct operation it is also possible to form a delta-modulated signal of the product of an analogue signal by a constant. The resulting modulated signal includes an error which is generally considered negligible. The hardware implementation of the method is both, simple and modular employing only conventional full adders and D-flip-flops. This leads to the possibility of realization of digital filters with straight delta-modulated input and output signals which are not intermediately transformed. Multiplexing for changing coefficients is also possible. View full abstract»

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  • 16. Dielectric loaded waveguides-a review of theoretical solutions. Part 2: Propagation through dielectric loaded waveguides

    Publication Year: 1965 , Page(s): 195 - 205
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (844 KB)  

    The paper presents an analytical survey of the propagation characteristics of microwaves through (i) dielectric loaded waveguides, such as parallel plane, rectangular, circularly cylindrical and coaxial guides filled inhomogeneously with one or two dielectrics; (ii) imperfect waveguides filled with imperfect dielectrics. The problem of the existence of backward waves in a circular cylindrical waveguide containing a concentric dielectric rod of smaller radius than the guide and the representation of equivalent circuit of a waveguide containing a dielectric post has also been discussed. A brief review of the theory of dielectrics has been included in the appendix. View full abstract»

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  • 17. A review of fault detection methods for large systems

    Publication Year: 1976 , Page(s): 276 - 280
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (727 KB)  

    A critique is made of current research into practical fault finding procedures for the maintenance of complex engineering systems. The half split and other methods currently in practice are analysed and their main weakness shown to be that no account is taken of the various costs involved. Also analysed are cost conscious methods which are useful in diagnosis training or in designing fault detection guides. A brief look is taken at advanced diagnostic techniques which are aided by an on-line computer in selecting the next test to be made. View full abstract»

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  • 18. High-frequency mixers using square-law diodes

    Publication Year: 1968 , Page(s): 311 - 316
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (505 KB)  

    The use of symmetrical and asymmetrical space charge limited (s.c.l.) square-law diodes as mixer elements is considered, and it is shown that low conversion loss is possible with the latter type. In order to achieve this a d.c. bias is necessary on the diode. Matching source and load resistances are higher than for the unbiased diode. The use of an idler termination at the sum frequency (p+q) is shown to have some advantages. The symmetrical diode is shown to be unpromising as a mixer element. View full abstract»

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  • 19. Admittance of a dipole antenna driven by a two-wire line

    Publication Year: 1976 , Page(s): 121 - 128
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (879 KB)  

    A new theoretical approach to the problem of the symmetric dipole antenna, driven by a two-wire line, is presented. The dipole and the line are treated as a unique boundary-value problem, and, as a consequence, a new, conveniently defined, apparent driving-point admittance is introduced. The analysis of the problem leads to a system of two integral equations with the dipole and line currents as unknown subintegral functions. The integral equations are solved approximately by using the so-called point-matching method. The current on the dipole is approximated by a polynomial with unknown coefficients and that on the line by a sum of incident and reflected travelling waves and a polynomial decreasing rapidly with the distance from the end of the line. Theoretical results, obtained by the present theory, reveal a strong dependence of the admittance on the distance between the line conductors. Excellent agreement between the theoretical and available experimental results is found. View full abstract»

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  • 20. Some partially active R filter circuits

    Publication Year: 1979 , Page(s): 587 - 590
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    A general circuit configuration is presented from which two bandpass and two lowpass filters can be derived as special cases. These are partially active R filters since each filter has one capacitor and realizes a second-order function by making use of an amplifier pole. View full abstract»

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  • 21. A ferrite ring stripline junction circulator

    Publication Year: 1966 , Page(s): 55 - 60
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (649 KB)  

    An essential feature of Bosnia's theory of the three-port stripline junction circulator is the smallness of the splitting of a degenerate pair of normal modes. This results in only a small asymmetric distortion of the isotropic field configuration in the disks. A new junction geometry is described which makes use of a garnet ring around a ceramic disk instead of the conventional garnet disk shape. When the degenerate modes of the two isotropic configurations are identical, the circulation adjustment for each geometry is nearly the same. This new circulator geometry is characterized by a low insertion loss and a large thermal capacity. View full abstract»

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  • 22. A high-speed tem junction ferrite modulator using a wire loop

    Publication Year: 1968 , Page(s): 81 - 82
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (227 KB)  

    In this note a new TEM junction switch is described which is based on the three-port junction circulator. Microwave switching is achieved by applying a current waveform through a single wire loop inserted in each of the ferrite disks. In this way the demagnetizing fields of the ferrite shape and the eddy currents in the junction housing are eliminated. The magnetic energy is now determined by the inductance of a single wire turn and is extremely small. The switch can either be continuously modulated by a square current waveform or can be latched by short current pulses between the two remanence states of the closed ferrite shape. View full abstract»

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  • 23. The mechanism of interference pick-up in cables and electronic equipment with special reference to nuclear power stations

    Publication Year: 1965 , Page(s): 149 - 158
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1287 KB)  

    The various forms of electrical interference in nucleonic reactor control equipment have been recently studied in the U.K.A.E.A. The results of this work are discussed and an analysis is made of interference due to interconnecting cables. Other causes of interference are mentioned and a method ofin situtesting is described which can be used to diagnose the sources of interference pick-up and to establish the interference sensitivity of a completed installation. View full abstract»

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  • 24. A method for the determination of the T-equivalent-circuit parameters of microwave structures

    Publication Year: 1977 , Page(s): 460 - 464
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    A method is described for the measurement of the equivalent circuit parameters of waveguide-mounted structures, such as a post or an inductive iris. Experimental results for post structures centrally mounted in X-band waveguides are also given. The values obtained are found to agree closely with those predicted from theory and the estimated accuracy is about 5%. View full abstract»

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  • 25. A sonar aid to enhance spatial perception of the blind: engineering design and evaluation

    Publication Year: 1974 , Page(s): 605 - 627
    Cited by:  Papers (31)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (3200 KB)  

    The design of an air sonar device with a new form of binaural display is described which aids the blind in perceiving their environment. Some of the limitations of knowledge of human perception and the influence this has on a specification for the device are discussed. Inherent limitations in the binaural aid both in terms of technology development and performance are also explained. The paper described what is expected of the man-machine control system in a mobility setting and discusses the technique of evaluating a manmachinesystem so as to assess the machine performance. View full abstract»

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  • 26. Theoretical and experimental methods for evaluating discontinuities in microstrip

    Publication Year: 1978 , Page(s): 73 - 84
    Cited by:  Papers (9)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1243 KB)  

    Microwave circuits generally include a number of junctions and discontinuities at the interconnection of the various circuit limits and the resulting parasitic reactances can have a major effect on the circuit operation. The designer of waveguide and coaxial circuits has had available, for many years, a wealth of information on the parasitic reactances associated with the circuit elements and discontinuities, such as bends, T-junctions, transitions. Many elements can be evaluated theoretically and very accurate measurement techniques have also been devised in both media. Furthermore, small adjustments to the final circuits may easily be made using tuning screws, movable short-circuits, etc. In microwave integrated circuits the theoretical evaluation of circuit elements and discontinuities is difficult, experimental measurement is of limited accuracy and adjustment of the final printed circuit not easy to achieve. This paper will review the available theoretical and experimental methods for evaluating such discontinuities and present the available range of results. The equivalent capacitances can be obtained theoretically using fairly well known techniques but the inductance calculations are more difficult, although some progress has been made in this area recently. Theoretical data are important as accurate experimental measurements require considerable effort and there are a large range of configurations in use. To illustrate the effect of discontinuities on practical design the case of a microwave f.e.t. amplifier will be taken. Significant design errors can be shown to occur if the discontinuities are not allowed for. However, by using the data we now have available on the parasitics, fairly simple modifications can be introduced in the initial design to enable the desired performance to be more directly obtained. View full abstract»

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  • 27. Techniques for utilization of hexagonal ferrites in radar absorbers. Part 1: Broadband planar coatings

    Publication Year: 1981 , Page(s): 209 - 218
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1307 KB)  

    The lack of suitable materials having permeabilities (¿r) greater than unity at microwave frequencies has previously made it difficult to design thin coatings of broadband radar absorbersat this frequency range. A possible solution is to utilize the hexagonal ferrites that exhibit significant ¿rvalues (¿5) over narrow frequency bands and this paper investigates methods of deploying this material to design thin broadband microwave absorbers. Several techniques are evolved involving layering of the materials and staggering of the material electrical parametersand dimensions to achieve a good match ofthe incident waves. The computed results are substantiated by measurements of the manufacturedmaterials; measurement techniques and details of the materials used are given in appendices. It is established that a planar absorbent sheet having a reflection loss > 10 dB over 5¿20 GHz is realizable within a practically acceptable thickness. View full abstract»

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  • 28. A high-gain multimode dielectric-coated rectangular horn antenna

    Publication Year: 1978 , Page(s): 439 - 443
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (413 KB)  

    A broadband high-gain dielectric-coated horn antenna operating in two orthogonal TE10+TE/TM12 and TE01 + TE/TM21 mode sets to generate circularly polarized elliptical shaped beam is described. The aperture E-field distribution can be tapered by virtue of the higher order TE/TM modes to cause the E-plane far-field beamwidth approximately equal to H-plane beamwidth of the other orthogonal set of modes, resulting in low off-axis polarization axial ratio. Because of the tapered aperture field distribution, the radiation patterns will also have low sidelobe levels. The radiation characteristics together with the on-axis gain of the antenna are derived from an electric vector potential on the basis of the vector diffraction formula. Analytical results are established in good agreement with experimental results on radiation pattern and gain measurements. This antenna which can be used as a communication satellite antenna to illuminate efficiently an elliptical zone on the earth surface will offer better directivity, high on-axis gain, low sidelobe levels and low cost. View full abstract»

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  • 29. Theory of reflections in a tapered waveguide

    Publication Year: 1966 , Page(s): 245 - 254
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1041 KB)  

    The tapered waveguide is regarded as a two-mode system, the modes being the forward and reverse waves. A reflection parameter can be defined, relating the amplitude of the reverse wave generated at a point in the taper to the amplitude of the forward wave at that point. The reflection parameter can be regarded as a coupling parameter between the two modes, and coupled-mode theory can be used to obtain theoverall reflection coefficient of the taper. It is shown how to estimate the error in this result. The error may become large if the frequency approaches the cut-off frequency of a guide whose cross-section is the same as that of the narrow end of the taper. The estimation of the error can be used to show how close to cut-off the theory is valid. A detailed analysis is given for the case of a homogeneously-filled tapered waveguide, with perfectly conducting walls, working in the dominant mode. The design of reflectionless tapers is discussed in the light of the results obtained. View full abstract»

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  • 30. Reflexion coefficient of a magnetized ferrite sphere in a rectangular waveguide

    Publication Year: 1974 , Page(s): 481 - 490
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1001 KB)  

    Work on small narrow resonance line-width ferrite spheres in waveguide leads to a need for theoretical quantitative understanding of the interaction between the ferrite and the waveguide fields. Analysis in the literature has previously relied on equivalent circuits with voltage and current, but belief that the concept of electromagnetic fields comes more naturally to waveguides led to the analysis in this paper. The main contribution is the derivation of an expression for the reflaxion coefficient presented by a small transversely magnetized ferrite sphere in a hollow rectangular metal waveguide propagating an H01 mode. The expression is valid for any location of the ferrite in the H-plane transverse dimension (a dimension) of the waveguide. From this general expression are derived subsidiary expressions for the impedance presented by the ferrite at four principal locations, at the centre, at the edge and in the two planes of circular polarization. The derivation of expressions for the H01 mode excited in a rectangular waveguide by a magnetic dipole is of interest outside the field of ferrite technology. Expressions are derived separately fortransverse and longitudinal orientations and hold good for all locations in the a dimension. View full abstract»

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  • 31. Digital encoding and filtering using delta modulation

    Publication Year: 1972 , Page(s): 547 - 551
    Cited by:  Papers (19)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1108 KB)  

    Digital filters are described which are based on delta modulation rather than pulse code modulation. It is shown that delta modulation encoding may be combined with digital filtering to realize either nonrecursive or recursive types. Conventional digital filter design techniques are applicable in both cases. Simulation of such filters on a small computer is discussed. Quantization noise is considered and comparisons made with the noise performance of the conventional digital filter. View full abstract»

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  • 32. A frequency meter with continuous digital presentation

    Publication Year: 1963 , Page(s): 109 - 113
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (581 KB)  

    Many transducers produce an alternating output with a frequency proportional to the transduced quantity. The normal method of converting this output into a suitable digital form is by counting the number of cycles that occur during a fixed time. This paper describes an alternative approach in which the binary number corresponding to the input frequency is continuously available. The system is based on the use of a reversible binary counter. The input frequency is converted into a suitable train of pulses and applied to the ADD input of the counter, and a second train of pulses whose mean frequency is proportional to the number stored into the counter to the SUBTRACT input. When equilibrium is established the number stored in the counter is proportional to the input frequency. View full abstract»

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  • 33. A survey of the techniques evolved for the measurement of position in numerically controlled machine tools

    Publication Year: 1963 , Page(s): 207 - 223
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (6900 KB)  

    The techniques described are divided into analogue and digitalmethods and the two categories are further subdivided where it is consideredlogical. The inherent sources of error in machine tools are briefly discussedand the basic types of control system are explained before enteringinto the detailed discussion of the transducers. View full abstract»

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  • 34. A side-lobe suppression system for primary radar

    Publication Year: 1964 , Page(s): 247 - 258
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2358 KB)  

    An auxiliary omni-directional receiving aerial and a logarithmic receiving channel identical to the radar receiving channel are used. A refinement of the system provides a sharp cusp in the omni-directional polar diagram coincident with the main lobe of the radar aerial. Nonlinear processing of the signals in the radar and omni-directional channels gives complete suppression of side-lobe signals. The operation of the system in the presence of jamming is examined. Illustrations are given of the performance of the system under several conditions. It is especially effective in suppressing pulse interference from other radars. View full abstract»

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  • 35. Dielectric loaded waveguides-a review of theoretical solutions. Part 2: Propagation through dielectric loaded waveguides (continued)

    Publication Year: 1965 , Page(s): 259 - 288
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2522 KB)  

    First Page of the Article
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  • 36. Dielectric loaded waveguides-a review of theoretical solutions. Part 3: The impedance approach to dielectric loaded waveguides

    Publication Year: 1965 , Page(s): 353 - 364
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1297 KB)  

    Surface impedance, transverse and longitudinal impedances are defined in analogy with the circuit theory definition. The concept of wave impedance and its relation to orthogonality of electric and magnetic fields is discussed. It is shown that in the case of multi-mode transmission, the wave impedance is not unique. Wave impedances of E and H modes in dielectric-filled waveguides and different impedance characteristics of a circular cylindrical waveguide containing two coaxial dielectrics and a coaxial guide containing two different dielectrics are discussed. View full abstract»

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  • 37. Radio frequency characteristics of carbon fibre composite materials

    Publication Year: 1981 , Page(s): 505 - 513
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1028 KB)  

    A comprehensive investigation of the r.f. properties of a range of samples of carbon fibre composite materials has been made. These samples were chosen as being representative of those which have been used or are likely to be used in aircraft construction. This paper is in two parts, first the investigations made to determine the electrical resistance characteristics of small samples of CFC materials in the frequency range from d.c. to 300 MHz, and the second part which describes the investigation of the screening performance of larger samples in the frequency range 0.15¿30 MHz for the magnetic mode and in the range 50¿1000 MHz for the electric mode. The methods of measurement which were developed during the investigation are described in detail together with the experimental results, and the conclusions include some indication of the implications of the installation of CFC panels for e.m.c. problems in aircraft. View full abstract»

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  • 38. A survey of millimetre-wavelength planar antenna arrays for military applications

    Publication Year: 1982 , Page(s): 543 - 550
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1186 KB)  

    The growing interest in the use of millimetre wavelengths for radar and communication systems stems principally from military requirements. Conventional component technology utilizing waveguides continues to feature but strenuous efforts are being made to devise new fabrication methods that lend themselves to further miniaturization, integration and cost saving. There is also a demand for a new generation of antenna types and this paper critically examines the progress made on planar antenna arrays using dielectric guides and substrate technology. Conclusions are reached on the feasibility of satisfying current system demands based throughout on published literature. It is conjectured that although the new planar devices have many performanceshortcomings compared to conventional antennas, cost, weight and size advantages are significant and could in some cases bring new system concepts for submunition systems. View full abstract»

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  • 39. Coupled-wave description of the absorption-type ferrite modulator

    Publication Year: 1965 , Page(s): 129 - 132
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (371 KB)  

    Coupled wave theory is applied to the absorption type ferrite modulator. The importance of the quantities (¿x¿ ¿y)/K and (ßx¿ßyK) in determining the attenuation of the incident polarization are thereby demonstrated. For maximum attenuation we require (¿z¿¿y)/K= ¿2 and (ßz¿ ßy)/K = 0. Some experimental data confirming the effect of the quantity (¿x¿ ¿y)/K on the loss of the incident polarization are given. View full abstract»

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  • 40. Z-transforms and their applications in control engineering

    Publication Year: 1965 , Page(s): 53 - 67
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1235 KB)  

    The paper describes the z-transform theory and its application. The background theory is built up in four stages from the continuous convolution integral, through the real-time impulse theory, to the z-transform. It is stressed that, unlike the Laplace transform, the z-transform is only an approximation. Engineering units are used throughout and emphasis is given to the correct representation of the sampler. The finite time of sampling is taken into account and it is shown how to make practical use of it. Illustrations of practical systems show good agreement with the calculations and attention is called to some common errors in the literature. The stability criteria are stated and methods of stability investigations are described. It is shown that for systems with zero-order hold circuits, the continuous Laplace transform is a more useful tool than the z-transform. The paper concludes with a practical approach to the design of discrete controllers. View full abstract»

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  • 41. The design of low-noise audio-frequency amplifiers

    Publication Year: 1968 , Page(s): 17 - 30
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1737 KB)  

    This paper contains: (a) an account of the phenomenological theory of noise in linear amplifiers operating from resistive signal sources; (b) a discussion of the noise parameters of bipolar and junction fieldeffect transistors; and (c) examples of how these principles can be applied in practical circuit design for resistive sources. View full abstract»

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  • 42. Some novel elements for delta-modulated signal processing

    Publication Year: 1981 , Page(s): 241 - 250
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (886 KB)  

    New and interesting multipliers are proposed to use for the direct-multiplication of delta-modulated signals by constants. In addition to a non-recursive form, three recursive-form delta multipliers are given. The recursive multipliers are suitable for multiplication by periodic numbers or by non-periodic numbers which can be approached by periodic ones. A significantly smaller number of delta adders is needed for the realization of recursive delta multipliers, than for the non-recursive ones. In addition, an interconnecting method is suggested, if the outputs of the multipliers are to be added. With the method a significant reduction of the scaling-down is achieved as well as a reduction of the total number of the necessary adders for the realization of the multipliers. The combination of interconnecting multipliers and delta doubters gives very good results for the realization of digital filters. View full abstract»

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  • 43. Radar pulse-compression by random phase-coding

    Publication Year: 1968
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1439 KB)  

    Integrated-circuit binary shift registers are used to realize the matched-filter to randomly coded radar signals. The system exploits the favourable range side-lobe properties of randomly changing binary codes to achieve pulse compression ratios greater than those obtainable with fixed coding schemes. The output noise distribution, signal/noise ratio, range resolution characteristics, range side-lobes and range ambiguities, and Doppler response of such a radar system are discussed. View full abstract»

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  • 44. Techniques for utilization of hexagonal ferrites in radar absorbers. Part 2: Reduction of radar cross-section of h.f. and v.h.f. wire antennas

    Publication Year: 1981 , Page(s): 219 - 225
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (857 KB)  

    Coatings of hexagonal ferrites on a wire antenna reduce its back-scattering radar cross-sections (r.c.s.) at microwave frequencies without causing significant deterioration of its radiation efficiency at the h.f. and v.h. communication bands. The back-scattering r.c.s. of an infinitely long conducting cylinder coated with a multilayer of hexagonal ferrites is derived and the result modified to take account of the finite length of a monopole antenna. Computed results for layered coatingsare presented to demonstrate the improvement in the microwave absorption bandwidth obtainable for a given coating thickness. It follows that the technique is best applied with all material and geometric parameters having tapered distribution and the ferrimagnetic resonances staggered over the required frequency band. Finally, the theory is illustrated by the measurement of the backscattering losses of a v.h.f. ferrite-coated antenna in the microwave frequency band (for both TM and TE polarizations of the incident waves) and its radiation performance at the v.h.f. range View full abstract»

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  • 45. Thin cylindrical antenna: variational solution with polynomial current approximation

    Publication Year: 1971 , Page(s): 493 - 500
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (967 KB)  

    All existing variational solutions to thin cylindrical antenna problems use two-term trial functions for currents, the form of which must either be based on some prior knowledge of current distribution along the antenna, or obtained by some other method. The present paper is aimed at eliminating these deficiencies in the applications of the variational method, by using as the trial function for current a polynomial of arbitrary order with complex coefficients. All the double integrals are transformed into sums of ordinary integrals to reduce computing time. The theory is applied to a number of isolated symmetrical cylindrical antennas of moderate lengths (up to approximately 2 ¿), starting with perfectly conducting dipoled ina vacuum, and ending with capacitively-loaded broadband cylindrical antennas. The theoretical results are in good agreement with available experimental data. View full abstract»

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  • 46. Semiconductors for microwave frequencies

    Publication Year: 1973 , Page(s): 75 - 81
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (983 KB)  

    Microwaves can now be processed by semiconductor structures, which are either a further development of the transistor for the lower microwave frequency ranges, or which use the non-linear behaviour of junction devices for mixing and parametric effects, particularly for low noise levels, or which exploit transit-time effects to create an effective negative conductance gd such as impatt and Gunn devices. The important role of material parameters is discussed New experimental results on gd vs. microwave voltage amplitude are presented for Gunn diodes as an illustration of the type of device characterization required. View full abstract»

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  • 47. The finite element method for potential calculations in a Hall plate

    Publication Year: 1975 , Page(s): 472 - 474
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (289 KB)  

    The potential equation in a Hall plate is solved by an expansion method. The first-order expansion can be replaced by a variational principle which enables the finite element method to be used. This technique can be applied to arbitrary geometries and numerical results are presented for a rectangular Hall plate. View full abstract»

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  • 48. A reappraisal of h.f. receiver selectivity

    Publication Year: 1982 , Page(s): 315 - 320
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    H.f. communication receivers have progressed towards a high level of sophistication yet a high percentage of reception failures are still due to limitations within the receiver. This paper considers the role of frequency selectivity for an ideal receiver and proposes a costeffective approach which should noticeably reduce reception failure. View full abstract»

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  • 49. Data compression techniques and applications

    Publication Year: 1980 , Page(s): 29 - 53
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (4199 KB)  

    Several data compression methods are reviewed for signal and image digital processing and transmission, including both established and more recent techniques. Methods of prediction-interpolation, differential pulse code modulation, delta modulation and transformations are examined in some detail. The processing of two-dimensional data is also considered. Results of the application of these techniques to space telemetry and biomedical digital signal processing and telemetry systems are presented. Some of the considerations and comparison criteria presented, even though not completely general because extracted from experimental results, can be useful in selecting and defining the more pertinent data compression system for the different practical applications. View full abstract»

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  • 50. UOSAT¿an investigation into cost-effective spacecraft engineering

    Publication Year: 1982 , Page(s): 363 - 378
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2965 KB)  

    The UOSAT Project commenced at the University of Surrey in 1979 to investigate the feasibility of, and the engineering problems associated with, the design, construction, launch and orbital operation of a relatively small and inexpensive spacecraft capable of a worthwhile contribution to the scientific, engineering and educational communities. The paper outlines the background to the project and the objectives of the UOSAT mission. After describing briefly the experiments on board the spacecraft, the paper deals with the design and fabrication of the satellite, the philosophies underlying these and the test and procurement procedures. Details of the project management and the resources necessary are given. The paper concludes with a summary of the present status of the spacecraft and its experiments. View full abstract»

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