Proceedings of the IEE  Part III: Radio and Communication Engineering
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Latest Published Articles

A history of the theory of information
Jan22 2010 
Microwave techniques for communication links
Jan22 2010 
The propagation of metre radio waves beyond the normal horizon. Part 2: Experimental investigations at frequencies of 90 and 45 Mc/s
Jan22 2010 
Discussion on the  Symposium of papers on microwave links  before the Radio Section, 9th April, 1952
Jan22 2010 
Radio Section: Chairman's address. The development and design of cooledanode valves
Jan22 2010
Popular Articles

The development of Qmeter methods of impedance measurement
Jan22 2010 
Surface waves
Jan22 2010 
The concept of an angular spectrum of plane waves, and its relation to that of polar diagram and aperture distribution
Jan22 2010 
Groundwave propagation over an inhomogeneous smooth earth
Jan22 2010 
Synthesis of ladder networks to give Butterworth or ChebÂ¿shev response in the pass band
Jan22 2010
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Popular Articles (October 2014)
Includes the top 50 most frequently downloaded documents for this publication according to the most recent monthly usage statistics.
1. The development of Qmeter methods of impedance measurement
Page(s): 295  302The Qmeter (or magnification factor meter) has become the recognized instrument for all kinds of r.f. impedance measurement. The resonant measuring circuit which forms the basis of such instruments may be excited from the oscillator source in different ways. In this paper, instruments have been classified into lowimpedance and highimpedance injection types, according to the systems employed. The lowimpedance resistance injection type has proved very satisfactory for use at frequencies below about 20 Mc/s. The various causes of error have been analysed and the difficulties of design for accuracy at the higher frequencies outlined. An instrument based on a novel principle of highimpedance injection has been developed, and it is possible to extend the range of accurate measurement to the region of 150 Mc/s. Slightly different technique is necessary when using the new principle, and illustrations of the use for various classes of measurement are given. A section of the paper is devoted to the definition of Q and the relationship between the quantities obtained on differing bases clarified. It is shown that the definitions of Q by frequency selectivity, by decrement, or by relation between energy storage and mean rate of dissipation are equivalent in the general case of a resonant system at a simple resonance. The essential difference between Qvalue and magnification factor, as measured by a Qmeter, is discussed in detail. View full abstract»

2. Surface waves
Page(s): 329  341The paper is an attempt to present, in the simplest possible terms, a unified picture of the theory of various forms of surface wave and a clear physical interpretation of their behaviour. The Zenneck wave, the radial cylindrical surface wave and the SommerfeldGoubau or axial cylindrical surface wave are each discussed and shown to represent basically one and the same phenomenon. The link with the Brewster angle, for which a wave incident on a surface suffers no reflection, is clearly established. The transition from a TEM wave supported by a parallelstrip transmission line, with metal plates close together, to two Zenneck waves independently supported by the plates, when these are separated by a very large distance, is demonstrated. The effect of bends in the supporting surface is considered, and methods of reducing radiation are explained. Finally the principles governing the launching of surface waves are surveyed with particular reference to the Brewsterangle approach. View full abstract»

3. The concept of an angular spectrum of plane waves, and its relation to that of polar diagram and aperture distribution
Page(s): 11  17A critical examination is made of the somewhat loose and incomplete statement that a polar diagram is the Fourier transform of an aperture distribution. By aperture distribution it is necessary to understand, in the twodimensional case, distribution across the aperture of the component along the aperture plane of the electromagnetic field in the plane of propagation. Furthermore, the concept of the polar diagram has to be replaced by that of an angular spectrum, except in the common case when the aperture may be considered more or less limited in width, and the field is being evaluated at a point whose distance from the aperture is large compared with the width of the aperture (and the wavelength). For example, it is convenient for some purposes to regard the problem of diffraction of a plane wave by a semiinfinite plane screen, with a straight edge, as a problem about an aperture distribution in the plane of the screen. This is a case for which the concept of a polar diagram is not in general applicable, and has to be replaced by that of an angular spectrum. The field at all points in front of a plane aperture of any distribution may be regarded as arising from an aggregate of plane waves travelling in various directions. The amplitude and phase of the waves, as a function of their direction of travel, constitutes an angular spectrum, and this angular spectrum, appropriately expressed, is, without approximation, the Fourier transform of the aperture distribution. If the aperture distribution is of such a nature that the concept of the polar diagram is applicable at sufficiently great distances, then the polar diagram is equal to the angular spectrum. But the angular spectrum is a concept that is always applicable, whereas the polar diagram is one that is liable to be invalid (for example, in the Sommerfeld theory of propagation over a plane, imperfectly reflecting earth). View full abstract»

4. Groundwave propagation over an inhomogeneous smooth earth
Page(s): 53  64The problem of groundwave propagation over an inhomogeneous smooth earth is discussed in terms of the known solution for a homogeneous earth. The inhomogeneity refers only to changes in the earth constants from place to place, and the problem is idealized by assuming a wave radiated from a vertical dipole over a series of homogeneous annular sections. After a statement of some of the conditions the solution would be expected to obey, including the essential one of reciprocity, some fundamental results of the theory for a homogeneous earth are described in a form directly useful to the argument. The solution is first given for the shortwave limit, where it is complete except in the neighbourhood of a boundary. By an approximate consideration of the energy flow at different heights above the ground, the solution is extended to the case of intermediate wavelengths where the first and last boundaries are in the diffraction region of the transmitting and receiving points respectively. It is then shown that a wellknown empirical method yields the same solution when it is made reciprocal by taking the geometric mean of the value it gives and the value that would be obtained with the transmitter and receiver interchanged. This method is formally used to obtain a tentative solution for the effect of the disturbance function in the neighbourhood of a boundary. It leads to the striking suggestion that on passing from a section of one value of conductivity to another of a higher one, there is a recovery in fieldstrength before the attenuation of the wave becomes characteristic of the new section. On crossing the boundary in the other direction, there is a correspondingly increased drop in field strength before the attenuation takes its new characteristic type. Owing to the lack of sufficiently controlled conditions, most of the existing experimental results are inconclusive with regard to these features at a boundary, but some evidence is given in support of them. Stress is laid on the need for further experiments specifically designed to study the field near a landsea boundary. The paper deals briefly with the practical application of the method, and gives a specimen fieldstrength/distance curve for a route consisting of several land and sea sections. It concludes by pointing out that further research is needed, especially with regard to the phase relationships, as the argument has dealt only with fieldstrength values. View full abstract»

5. Synthesis of ladder networks to give Butterworth or ChebÂ¿shev response in the pass band
Page(s): 115  118First Page of the ArticleView full abstract» 
6. Waveguide Attenuation and its Correlation with Surface Roughness
Page(s): 85  90Measurements of the attenuation produced by airfilled drawn waveguide tubing have been made at a frequency of 9375 Mc/s. The theoretical and experimental performances of various waveguide surfaces are compared and discussed. Detailed studies of the roughness of the internal surfaces of certain standard commercial waveguides have been made, to determine the orders of magnitude of the irregularities and to try to set up a correlation between measured and calculated attenuation values. It is concluded that the discrepancies between these values are due solely to surface roughness, and it is doubtful whether further improvements in surface finish over that of present precisiondrawn tubes are required for any applications at frequencies near or below 24 000 Mc/s. The effects of small changes in waveguide dimensions on attenuation, together with the problems involved in measuring both the attenuation and d.c. resistivity of a waveguide sample, are considered. View full abstract»

7. The electrical breakdown strength of air at ultrahigh frequencies
Page(s): 117  129The breakdown strength of air has been determined for alternating electric fields of frequencies between 100 and 300 Mc/s. Parallel plane gaps up to 1 mm wide have been investigated. A description is given of the apparatus employed, together with details of a dielectric voltmeter which has enabled the voltage across the breakdown gap to be measured accurately. A discontinuity is shown to exist in the relation between the breakdown stress and the gap width. The breakdown stress for small gap widths appears to follow a curve representing values some 10Â¿15% below those obtained with direct current. At a critical gap width, which is dependent primarily on the frequency of the applied electric field, there is a sudden decrease in the electric stress at which breakdown occurs, to a constant value, which for atmospheric pressure is 29 kV/cm. The critical gap width is found to vary slightly with gas pressure, and may be increased by the application of a small d.c. electric field across the gap. An examination of the results shows that under transition conditions Paschen's law is not applicable. A theory is put forward on the basis that breakdown may be initiated in one of three different ways, each of which may be represented by a curve that separately obeys Paschen's law. View full abstract»

8. Information theory and inverse probability in telecommunication
Page(s): 37  44The foundations of information theory are presented as an extension of the theory of inverse probability. By postulating that information is additive and taking suitable averages, all the essential definitions of Shannon's theory for discrete and continuous communication channels, with and without noise, are obtained. The theory is based on the idea that receiving a communication, or making an observation, merely changes the relative probabilities of the various possible messages. The whole process of reception can therefore be regarded as a means of evaluating a posteriori probabilities, and this leads to the idea that the optimum receiver in any telecommunication problem can always be specified, in principle, by inverse probability. The simplest instance is the correlation receiver for detecting very weak signals in the presence of noise, and its theory is briefly discussed The paper concludes with an answer to possible criticisms of the use of inverse probability. View full abstract»

9. Delay networks having maximally flat frequency characteristics
Page(s): 487  490A lumpedconstant equivalent of a transmission line can be obtained in general in the form of a symmetrical lattice, in which the series and lattice arms are inverse and approximate respectively to the shortcircuit and opencircuit impedances of half the line. One such set of approximations can be derived from the infinite ladder networks (Cauer's canonical form) equivalent to these impedances. These approximations produce allpass constantimpedance networks (dissipation being neglected) in which the delay is maximally flat in the sense that the first 2m Â¿ 1 derivatives of the delay with respect to frequency are zero at the origin; m is an integer expressing the order of the approximation. View full abstract»

10. The Use of Bessel Functions for Calculating the SelfInductance of SingleLayer Solenoids
Page(s): 133  137This paper is a continuation of the paper on ?The Field of a Coil between two Parallel Metal Sheets.? It was pointed out in Section 6 of that paper that the general expressions, which had been developed therein, made it possible to calculate both the selfinductance and the highfrequency resistance of any circular coil enclosed in a closed screeningcan. This solution was not then developed, but the work is in progress now. As a preliminary to this said new work it seemed desirable to show first that the Bessel function treatment did yield the correct result for the selfinductance of a singlelayer solenoid. This exploration has shown that the old problem can be attacked with great elegance by the Bessel process and that it has definite merits of its own. This is perhaps not surprising, since the form of a solenoid suggests that Bessel functions are more appropriate to it than the integral of elliptic functions. This paper sets out the solution of an old problem by a new means. The first stage shows that the extremely general Bessel formulae do lead to the wellknown expression H = 4?IT cos ? for the magnetic field at the centre of a solenoid. To obtain this result, use has to be made of formulae for the infinite integral of products of Bessel functions, and in particular to one formula due originally to Heaviside. The Bessel treatment turns out to have special advantages for calculating the strength of the field just inside the winding: this evaluation is necessarily peculiarly cumbersome by Legendre functions because they are in a series which is verging on becoming divergent at this radius. Formulae typified by eqn. (10) in the paper have a certain element of novelty and are valuable for calculating the highfrequency resistance of a coil having only one turn. The inductance of the isolated solenoid is derived in Section 2, and the results are tabulated and compared with values derived by Dr. A. Russell: also it is shown that the results can be expressed as t t he sum of two integrals, the one or other of which becomes relatively unimportant when the coil is either long or short. The process of addition is exhibited graphically in Fig. 2; this Figure exposes very clearly the structure of the whole calculation, which otherwise remains obscure right up to the final result. Section 3 is devoted to calculating the inductance of any solenoid placed symmetrically between a pair of infinite sheets of metal, perpendicular to its axis. The tabulated results are useful for estimating the order of magnitude of the effect of a large metal sheet; and also they establish that the inductance of a long, isolated solenoid may be calculated by means of a rapidly convergent series without resort to the much more cumbersome process of using the definite integral. Though most of the results are old, the process of deriving them is believed to be novel. The new method is found to have some advantages over the old, and moreover it will solve many problems which are insoluble by the old. It is hoped that the new solutions will follow shortly; this paper is a necessary preliminary to the exposition of them. View full abstract»

11. The reflection of electromagnetic waves from a rough surface
First Page of the ArticleView full abstract» 
12. Some considerations in the design of negativefeedback amplifiers
Page(s): 138  158A brief survey is made of the application of a phaseamplitude theorem, due to Bode, to the design of feedback amplifiers with constantphase margins, and a graphical method of estimating the phase change at any frequency from a knowledge of the amplitude characteristic is described. The use of constantphase margin as a design criterion is criticized, and justification is given for a new criterion termed Â¿stability margin.Â¿ Using this criterion, a technique is developed for employing several feedback paths, thus enabling an increased amount of feedback to be connected to circuits of increased complexity. A brief account of a miniature audio amplifier with two feedback paths is included, and a 100watt amplifier covering 300 c/sÂ¿108 kc/s with some 35 db of feedback is described which, although it is Â¿conditionallyÂ¿ stable, is suitable for use in a multichannel telephony system. View full abstract»

13. A New Approach to the Design of SuperDirective Aerial Arrays
Page(s): 303  314The current distribution required for maximum directivity of an array with a finite number of elements and any specified geometrical configuration is shown to be completely defined by the self and mutual resistances of the elements and by a certain component of the voltage (the Â¿resistance voltageÂ¿) across the terminals of each element. This voltage component is required to vary from element to element in the same way as the instantaneous local values of a sinusoidal disturbance travelling across the array, in the direction under consideration, with the velocity of an electromagnetic wave. As a consequence, the maximum gain of the array is expressible either as a double sum containing only the mutual conductances between the individual elements multiplied by trigonometrical factors depending on their spacing, or as an expression identical (except for a numerical factor) with that for the distant field of the array. These theorems hold, slightly modified, for arrays of nonidentical elements. The theory has been applied to the numerical calculation of certain simple arrays. It appears that, for arrays of a given size, directivities greater than those obtained by conventional design methods can be achieved without excessive losses. This has been substantially confirmed by an experimental array of four elements operating at 75 Mc/s. The theoretical gain was 10.1 db, while 8.7 db was measured. Of the discrepancy, 0.6 db was calculated to be due to losses in the feeder system and a further 0.2 db to losses in the dipoles. The bandwidth was about Â±Â¿ Mc/s for a drop in gain off Â¿ db. The degree of superdirectivity is indicated by the fact that a physically identical array fed with equalamplitude currents phased for maximum field strength in the endfire direction would have a gain of 4.6 db. View full abstract»

14. A relation between the Sommerfeld theory of radio propagation over a flat earth and the theory of diffraction at a straight edge
Page(s): 18  27A new way of visualizing the Sommerfeld theory of propagation over a flat, imperfectly reflecting earth is presented. The Sommerfeld theory arises because the ray theory of propagation from a source in the presence of a flat, imperfectly reflecting earth is only an approximation. The ray theory involves the assumption that the Fresnel reflection coefficient of the earth does not vary rapidly with angle of incidence, and this assumption is not satisfied for glancing incidence of vertically polarized waves on the earth's surface at broadcasting wavelengths. The main object of the new presentation is to facilitate the solution of problems involving propagation near the surface of the earth partly over land and partly over sea, but these applications are not included in the paper. It is convenient to think of a twodimensional problem in which the transmitter is a line source parallel to the earth's surface, having a vertical polar diagram of circular shape. Such a source may be Fourier analysed into plane waves whose directions are distributed in a vertical plane of propagation perpendicular to the line source; the amplitudes of all the plane waves are the same and they are in the same phase at the source. When these waves are reflected from the earth they produce an angular spectrum of reflected waves, the amplitudes and phases of which are determined by the Fresnel reflection coefficient. This angular spectrum could be thought of as arising, in the absence of the earth, from an aperture distribution on the vertical plane through the primary line source. The aperture distribution that produces the angular spectrum of reflected waves in this way is the exact image of the primary source in the imperfectly reflecting earth, and is given by the Fourier transform of the Fresnel reflection coefficient. For a perfectly conducting earth this aperture distribution reduces to a line source identical with the primary source and located at the optical image line. The correction required to this when the earth is not perfectly conducting is mainly the following. An aperture distribution extending indefinitely downwards from the image line must be introduced, and this consists essentially of the aperture distribution produced by diffraction of the Zenneck wave under a screen extending from the image line upwards. The field produced by the primary source in the presence of the imperfectly reflecting earth is thus the field that would be produced with an almost perfectly conducting earth, together with the field arising from diffraction of the Zenneck wave under the image line. If diffraction of the Zenneck wave under the image line is calculated by the edgewave approximation we merely arrive at the ray theory of reflection from the earth of radiation from the primary source: the edge wave from the image line, together with the wave from an image in an almost perfectly conducting earth, makes up the wave from the Fresnel image for the imperfectly reflecting earth. But, at broadcasting wavelengths, points close to the earth are often too close to the shadow edge, formed by diffraction of the Zenneck wave under the image line, for application of the edgewave approximation. We then have to apply the full theory of edgediffraction based on the Cornu spiral, and this gives the Sommerfeld theory. View full abstract»

15. Code convertors for the interconnection of Morse and teleprinter systems
Page(s): 151  157Automatic convertors from international 5unit teleprinter code to international Morse code, and vice versa, are described, different equipments being used for the two directions of conversion. Since the transmission speeds of teleprinter and Morse circuits are not, in general, the same, some form of storage is necessary when information in one code has to be received over a circuit, converted to the other code and retransmitted over another circuit. Morse (or Wheatstone) perforated tape is the form of storage adopted. Where an electromechanical device already in production could be simply modified to perform a function required in either of the convertors, it has been utilized in the designs. The input to the Morseteleprinter code convertor is in the form of Morse perforated tape, and the tapereading mechanism of a standard Morse printer has been adopted. Similarly, the selecting and perforating mechanism of a Morse keyboard perforator has been incorporated in the teleprinterMorse convertor to provide the Morse perforatedtape output. The remainder of the equipment is mainly electronic, containing both thermionic and coldcathode valves. View full abstract»

16. A storage system for use with binarydigital computing machines
The requirement for digital computing machines of large storage capacity has led to the development of a storage system in which the digits are represented by a charge pattern on the screen of a cathoderay tube. Initial tests have been confined to commercial tubes. Shortterm memory of the order of 0.2 sec is provided by the insulating properties of the screen material. Longterm memory is obtained by regenerating the charge pattern at a frequency greater than 5 c/s. The regeneration makes accurate stabilization of the position of the charge pattern on the c.r. tube unnecessary. The properties required of a storage system, and its operation as part of a machine, are stated. If such a machine were operated in the series mode, an instruction would be set up and obeyed in 600 Â¿sec. View full abstract»

17. The transmission of pictures by radio
Page(s): 325  334The paper describes the development of picturetelegraphy equipment since Alexander Bain's first proposals in 1842, and particularly the applications to radio working since the first transatlantic tests in 1924. The technique depended on the type of radio circuit available, commencing with lowfrequency highpower transmitters, then highfrequency beamtelegraph transmitters, frequencymodulated subcarriers on doublesideband telephone transmitters and finally frequencymodulated singlesideband transmitters. The use of conventional amplitudemodulated transmitters has never been possible, first because such methods were not admissible on lowfrequency circuits and later because the final fading ratios were too high to permit satisfactory reproduction of tone values. Methods of visual recording which preceded photographic reception included the use of hot wax, ink and hotair jets and electrolytic paper. Spurious patterns caused by mechanical imperfections and means of avoiding them are described. Synchronizing methods have developed from elementary tuningforks to quartz crystals. The comparatively low limit to speed of operation passed from equipment difficulties to that set by the propagation of highfrequency signals through the ionosphere. The effect of multipath transmission is discussed. Consideration of bandwidth requirements discloses the inefficiency of facsimile methods for the transmission of telegrams. View full abstract»

18. The Design of Metallic Delay Dielectrics
Page(s): 45  48A theory of metallic delay dielectrics, which is more accurate than existing ones and is based on an analogy with shuntloaded transmission lines, has been developed for the simplest case, when the delay medium consists of an array of infinitely long conducting strips. Formulae have been obtained for the refractive index, impedance and cutoff wavelength of such a medium, and the more important results are presented graphically. A procedure for designing such dielectrics to have a desired refractive index is outlined, and some limitations in the use of metallic delay lenses are pointed out. View full abstract»

19. The Reflectometer
Page(s): 25  30The paper describes a type of directional coupler called a reflectometer used for connecting test equipment to a radiofrequency transmission line. A single loop of wire with a resistor in one arm is mounted at a fixed point and is loosely coupled to both the electric and the magnetic fields of waves in the line. The relative phase of the two fields for a travelling wave depends upon the direction of propagation, and the couplings with these fields are arranged to cancel for one direction of propagation and add for the other. Thus the coupling will detect, or launch, waves travelling in one direction only. This type of coupler was used originally in America to measure the reflected waves in a 400Mc/s coaxial feeder: hence the name Â¿reflectometer.Â¿1, 2 In the present paper the general theory is given, and a design suitable for waveguides at a wavelength of 10 cm is described. Applications to the monitoring of standing waves and transmitted power in a radar transmitter system and to the testing of radar receiver sensitivities are considered, and the methods which make use of a reflectometer are shown to have considerable advantages over others. View full abstract»

20. Crystal diodes
Page(s): 157  168The first part of the paper gives the current views of the manner in which very small amounts of impurities give rise to the special electrical properties of semiconductors, and of the mechanism of contact rectification. The preparation of germanium and silicon for use in crystal diodes is considered and the steps found necessary in the processing are discussed in terms of the theoretical ideas. In the second part of the paper, the design and performance of (a) a new coaxialtype siliconcrystal diode intended for use as a mixer at frequencies up to about 10 000 Mc/s, (b) a wireended germaniumcrystal diode, are described and discussed. Particular attention is given to the frequency dependence of the rectification efficiency of the germanium diode, and its application as a replacement for the thermionic diode. View full abstract»

21. Polyphase modulation as a solution of certain filtration problems in telecommunication
Page(s): 349  358An important class of filtration problems in telecommunication is associated with frequency changing; it includes the generation and demodulation of singlesideband carrier channels and the elimination of imagefrequency interference in heterodyne demodulators, such as the superheterodyne radio receiver or the conventional wave analyser. Filters for these applications are often difficult to design or realize, or may be inconvenient on account of variable tuning, etc. It has been realized recently that polyphase modulation can be used as part of the frequencychanging process with great advantage. It can eliminate the need for difficult or inconvenient filters, although other design problems are introduced which may some times be as difficult to solve. But there is no doubt that the idea of polyphase modulation is of great importance in telecommunication theory and practice. The basis of the advantages given by polyphase working is that polyphase signals possess an identifying property additional to that of frequency, namely sequence. By using circuits which distinguish between signals of the same frequency but opposite sequence, it is possible, without any preliminary filtration, to separate signals which lie in the same frequency band after modulation, and which, therefore, could be separated by normal means only by filters before the modulation stage. The first Section of the paper outlines the main filtration problems which can be tackled by polyphase methods, and then the necessary polyphase theory is given. This is followed by a discussion of circuit design for polyphase modulation and sequence discrimination. The list of references shows that there have been many publications covering some of the separate applications of this work, but the paper is believed to present for the first time a comprehensive theory of polyphase modulation embracing all the known applications. View full abstract»

22. Waveform responses of television links
Page(s): 258  270Referring particularly to pointtopoint links, the paper is concerned with the longoutstanding problems of measuring and specifying the transmission performance of those parts of a television system which can be treated as linear networks. Such problems are more easily studied in terms of waveform responses than of steadystate characteristics, because the permissible distortions of television signals can be expressed more directly in terms of time than of frequency. Studies have been somewhat hampered by the dearth of published information on waveform responses taken under practical everyday conditions. The paper offers assistance by giving typical examples from a series of tests, made by the Post Office with the cooperation of the British Broadcasting Corporation, on some of the links and items of equipment used in the 405line system. The responses were taken with the aid of a set of sinesquared pulse and other test signals shown by experience to be particularly convenient for the purpose. Two complementary methods of specification are proposed, one for rapid routinetesting purposes, and the other to meet the more precise requirements of acceptancetesting work. Both methods are framed in terms of a Â¿rating factor,Â¿ the value of which can be varied to provide any desired degree of stringency. The acceptancetest method takes advantage of the simplification afforded by the timeseries method of expressing waveform responses. View full abstract»

23. An investigation of the characteristics of cylindrical surface waves
Page(s): 321  328Some quantitative measurements on cylindrical surface waves have been made at a frequency of approximately 10 000 Mc/s. For this purpose an axial standingwave indicator and an instrument for determining the radial field distribution have been designed and tested by application to a wave of known configuration. The axial standingwave indicator was used for simple impedance measurements and is now established as a practical device. A series of quantitative observations on cylindrical surface waves have been made with the instrument for examining the radial field distribution, which at a long distance (say 30 ft) from a launching horn, was found to agree with that expected from theory. In the case of thin bare copper wires and enamelled wires of small size the radial decay coefficient deduced from the fielddistribution graph approximated closely to the value obtained from the SommerfeldGoubau theory. On the other hand, the field distribution in the vicinity of the horn was always considerably distorted by radiation from the horn. For accurate work in the limited space available, it was found necessary to dispense with the horn and set up a surfacewave resonator. This arrangement is capable of yielding the same information on field distribution, since the standingwave and travellingwave patterns are identical. The wavelength of the surface wave supported by the resonator at its resonant frequency was measured by a special method described in the paper, and from a knowledge of the resonant frequency the decay coefficient was calculated. Measurements on No. 24 S.W.G. copper wire thickly coated with polythene showed that the corresponding values of the decay coefficient derived from the Goubau approximate theory were greatly in error. This applied in particular to conductors having a coating of polythene whose thickness exceeded 0.010 in. A curve relating the coating thickness with the measured decay coefficient was obtained and compared with the Goubau predictions. Later the assumptions made in the original theory were revised, and accurate curves displaying the dependence of the decay coefficient on the thickness of dielectric coating, wire diameter and frequency were computed. These curves were found to be in agreement with the experimental results. The surfacewave resonator can also be used for the measurement of surface reactance of corrugated surfaces. View full abstract»

24. A wideband waveguide phaseshifter
Page(s): 117  124A method is described of constructing waveguide phaseshifters well matched over a broad frequency band. The principles of design are discussed, and details are given of the performance of experimental Sband models having bandwidths of 10Â¿25%. View full abstract»

25. The accuracy of the location of sources of atmospherics by radio directionfinding
Page(s): 383  390In recent years, increasing importance has been attached to the use of radio directionfinders for the location of thunderstorms. A large number of stations for this purpose are now in operation, and for the planning of further networks it is necessary to assess the accuracy to which storms may at present be located, and to delimit the areas in which location is satisfactory with the existing networks. An investigation of the accuracy of the United Kingdom network of twinchannel cathoderay directionfinders, operating at frequencies near 10 kc/s, has shown that instrumental errors other than polarization errors are small, but that at particular stations, errors of several degrees have been caused by the hilly nature of the terrain and by buried cables. When the equipment is on a level site, free from obstructions, polarization errors are likely to be the main limitation to accuracy, particularly at distances of a few hundred kilometres and at night. Maximum errors of 2? or 3? may be expected in summer daytime and rather more in winter daytime. The magnitudes of polarization errors at night are not accurately known. Over a limited range of distance, around 400km, observations on continuouswave stations exhibit, at times, r.m.s. errors of more than 20?, but there is evidence that errors of this magnitude do not normally occur with atmospherics. At distances greater than 1 000km, polarization errors may be expected to be no greater than 2? or 3?, even at night. At these distances there are also significant errors caused by interference between the atmospheric under observation and others arriving almost simultaneously. Although knowledge of the errors is far from complete, preliminary estimates of their magnitudes have been made and an estimate of the accuracy of storm location has been derived. It is not possible to express the potential accuracy in simple terms, since it depends not only on the bearing errors, the spacing of the stations and the distance of the  storm, but also on the number of observations made and the manner in which they are interpreted. As an indication of the order of magnitude, it is estimated that with the present network and observation technique the probable error in position of a storm centre at a distance of 1 000km is about 20km by summer day, 50km by winter day and 100km by night. These preliminary estimates, particularly that for nighttime conditions, must be regarded as approximate because knowledge of the bearing errors is still lacking in some important respects. In particular, a more complete knowledge is required of their amplitude distribution and of the degree of correlation, if any, between polarization errors at the different stations. The types of error discussed are liable to occur with all atmospherics directionfinders in current use; polarization errors, in particular, may be expected with any instrument with an aerial system incorporating either a single rotating loop or a pair of fixed crossedloops. View full abstract»

26. Noise in silicon microwave diodes
Page(s): 317  324The various kinds of noise fluctuation which occur in silicon microwave diodes are discussed in the light of measurements at widely differing frequencies of the noise produced when the diodes are excited by d.c. bias. It is found that flicker noise which is dominant at 1 600 c/s may extend to 45 Mc/s and beyond. By selecting diodes for low noise output and restricting the measurements to low bias currents, good agreement is found at 45 Mc/s with the calculated values of shot noise; it is established, in particular, that the thermal noise which occurs for zero bias may be calculated in terms of the shotnoise concept. In the region of 30 000Â¿40 000 Mc/s the noise produced by reverse bias is probably attributable entirely to shot noise. Finally the bearing of these measurements on the problem of noise during mixer operation is discussed briefly. View full abstract»

27. A WideBand Oscillator using a ConicalHelix Tuning Inductor
Page(s): 165  170The paper describes a wideband oscillator (frequency variation, 1:45) using a single tank circuit between the grid and the anode of a triode. The frequency control is made flexible by the use of conical helices (instead of the usual cylindrical ones) as inductance. Two conical helices connected at their apices by a large capacitor are connected to a pair of variable cylindrical capacitors. For the highfrequency end, the leads connecting the coils to the grid and the anode are used as transmission lines, the main tuning circuit being automatically isolated. The use of the conical form of inductance makes the transition from the transmissionline mode of operation to LCmode of operation and vice versa smooth, and also keeps the undesirable coupling between the used and unused portions of the inductance small. Methods of calculating the oscillation frequency in terms of the circuit parameters are described. In an experimental set tested conical helices of seven turns each were used (diameter of the largest turn, 6.0 cm) and the components were so mounted that by turning a single control the frequency could be varied from 10 to 450 Mc/s. The speed of variation of the frequency with the turn of the control can be regulated by adjusting suitably the geometry of the tank circuit (coil and capacitor). The output power can be smoothed to any desired extent throughout the range by means of a variable output coupling. View full abstract»

28. Circuit technique in frequencymodulated microwave links
Page(s): 256  274The paper describes the circuit problems in wideband microwave communication links and is illustrated by reference to the development of links operating at frequencies around 4 000 Mc/s for 180channel telephony and for television. Modulating and demodulating circuits with very linear characteristics, and i.f. amplifiers with uniform timedelay are described, together with the necessary techniques required to assess their performances. The optimum design for a broadband lownoise i.f. amplifier is shown to consist of cascaded earthedgrid triodes. Automaticfrequencycontrol systems, the special video problems of television, and highlevel intermediatefrequency/microwave mixers are described. View full abstract»

29. Some recent developments in phototelegraphy and facsimile transmission
Page(s): 344  359The paper deals with development work on which the authors have been engaged since 1945 on machines for the transmission of pictures and facsimiles over landlines and radio. Faithful tone reproduction of photographic material has been attained, and machines have been produced to fulfil the needs of the Press. Machines with more precise scanning, up to 500 lines per inch, have been developed. A method of controlled retoning of a picture is also described. Further developments have been made using an electrochemical action instead of photographic paper as the recording medium. Machines have been produced to receive tone pictures and to act either independently or as monitors to the photographic machines. Recent applications of the electrochemical recorder to facsimile and telegraph purposes are described. View full abstract»

30. Some Adverse Influences of Meteorological Factors on Marine Navigational Radar
Page(s): 26  36The absorption of electromagnetic waves in the atmospheric gases, and their absorption and scattering by various forms of precipitation, are discussed from the aspect of their effects on the performance of centimetrewave radar equipment. Particular attention has been devoted to the phenomena to be expected at the wavelength of 3.2 cm, since this is the wavelength now used, and likely to be more widely used, for marine navigational radar. At a wavelength of 3.2 cm, absorption by the atmospheric gases is hardly significant, and absorption and scattering in rain are likely to cause most of the appreciable reductions in the range of detection. Whilst it is not possible to make a complete generalization, it appears that, at this wavelength, the deterioration in radar performance on targets having echoing areas greater than, say, 2 000 m2 (e.g. ships of more than about 10 000 tons) arises mainly from attenuation produced in rain rather than as a result of masking by echoes from the precipitation itself. With smaller targets, however, this masking will often be the more serious factor. The heavy rates of rainfall common in tropicalequatorial regions will produce a much greater deterioration in radar performance than will the rainfall likely to occur at all frequently in temperate regions. Although very intense snowstorms can produce echoes sufficiently strong to be troublesome, the rate of precipitation required is such that its frequency of occurrence is unlikely to be great. Attenuation occurring in snowfalls is generally of little importance. In dense fogs reductions in detection range may be appreciableÂ¿especially in polar regionsÂ¿when the optical visibility falls below about 25 m; in this case, attenuation is the significant factor. View full abstract»

31. The measurement of permitivity and power factor of dielectrics at frequencies from 300 to 600 Mc/s
Page(s): 303  311The paper describes a resonance method of measuring permittivity and power factor which is essentially a development of the Hartshorn and Ward apparatus, suitable for use at the higher frequencies. The method is one of capacitance variation, and the disc form of sample, the circular plate electrodes and the cylindrical form of micrometer capacitor are retained but reduced in linear dimensions. The capacitive elements are mounted in a reentrant cavity, and the micrometer capacitor is so placed that the voltage across it is only a fraction of that across the plate electrodes; this increases the fineness of adjustment. The micrometer capacitor can be calibrated only by using the cavity as a wavemeter; the capacitance settings were therefore expressed in terms of the corresponding resonance frequencies, and the calculations of power factor then became identical in form with those of the frequencychange method, although the measurements were made at a constant frequency. After applying the appropriate corrections the permittivity can be determined to within Â± 1% over most of the range. The high Qfactor of the cavity and the precision of adjustment of the micrometer capacitor make the powerfactor determinations highly accurate. For values less than about 0.01 the error is estimated as being less than Â± 2 Ã 10Â¿5 (for measurements on solids). For higher values a superheterodyne receiver incorporating a piston attenuator is used as the detector, and the estimated limits of error for such measurements are Â± 5 Ã 10Â¿4. View full abstract»

32. Analysis of a transmissionline type of thermionicamplifier valve
Page(s): 114  115First Page of the ArticleView full abstract» 
33. QuarterWavelength CoaxialLine Resonators for BetatronStarted Synchrotrons
Page(s): 508  516The paper describes the design of quarterwavelength coaxialline resonators, suitable for use in betatronstarted synchrotrons giving energies less than 400 M.eV. The description is illustrated by measurements on the resonators which have been incorporated in 8M.eV and 30M.eV synchrotrons. View full abstract»

34. The design of a radiofrequency coaxial resistor
Page(s): 48  50First Page of the ArticleView full abstract» 
35. Artificial dielectrics having refractive indices less than unity
Page(s): 319  320First Page of the ArticleView full abstract» 
36. Reflection and refraction of microwaves at a set of parallel metallic plates
Page(s): 47  55The paper deals with the theory of the propagation of microwaves, passing from a homogeneous and isotropic medium into a set of parallel metallic plates. The plane of separation between the set of plates and the homogeneous medium outside is assumed perpendicular to the plates. The incident wave is plane, and its direction of propagation is in the plane containing the perpendiculars to the plates and to the surface of separation. The electric field is parallel to the plates. The method is relatively simple. The study is based on Maxwell's equations and on periodicity and continuity considerations. An analytic method is introduced for the solution of the infinite set of linear equations with an infinity of unknowns, which arises from the continuity conditions at the boundary plane of the plate edges. Formulae are obtained giving the nature, direction, phase and amplitude of the reflected and transmitted waves. The reflected waves follow the usual laws found in the grating theory. In the case when only one nonevanescent plane wave is reflected, the transmission and reflection power coefficients are those obtained at the junction of two semiinfinite transmission lines corresponding to the freespace and the plate medium respectively. The analogy with transmission lines is more complex when two nonevanescent waves are reflected. For the usual angles of incidence and plate spacings the transmission power coefficient is high (maximum 99.5%), and the phase shift on transmission is small. View full abstract»

37. The Measurement of the Phase Velocity of GroundWave Propagation at Low Frequencies over a Land Path
Page(s): 73  84The paper describes the measurement of the change of phase with distance of a 127.5kc/s wave over a particular inhomogeneous land path and the deduction of the mean velocity. The measuring system made use of transmissions from stations of the English chain of the Decca Navigator System, and the path studied was that between the Lewes (Sussex) and Warwick stations (177 km). With the aid of a mobile phasemeasuring equipment the difference between the phase of the signal from one transmitter and that of the signal from the other transmitter was measured with an accuracy of 0.25Â° at 25 points along the path. From these results and a knowledge of the exact position of the points it was possible to plot a curve showing the deviation of the measured phase from that calculated on the assumption of a velocity equal to that in free space. The mean velocity deduced for the path was 299 230 Â± 12 km/sec. An examination was made of the measured change of phase along the path in relation to the profile and geological structure. Although there was no definite evidence of the phase of the wave being affected by the ground contours, the influence of the nature of the soil was very marked. A detailed study of the geological structure was undertaken and the electrical characteristics of each section of the path were assessed. A high velocity over ground of good conductivity and a low velocity over ground of poor conductivity was clearly shown. Comparisons between the measurements and the phase changes derived by a method based on theoretical curves of phase lag over homogeneous ground showed good correlation. They also confirmed the theoretical predictions of a characteristic phase disturbance at the boundary between sections of differing conductivity. It is concluded that this method of phase determination over an inhomogeneous path is one which offers a good approximation to the phase changes actually taking place. View full abstract»

38. Wideband foldedslot aerials
Page(s): 414  418Among the possible applications of Babinet's principle proposed by C.E.G. Bailey and H.G. Booker was the Â¿folded slot,Â¿ the slot analogue of the wellknown folded dipole. The paper describes modified forms of folded slot designed to exhibit reactance compensation, so that the variation of impedance over a wide band of frequencies is small. Calculation of the input impedance is facilitated by considering an equivalent circuit which applies to certain types of 3terminal network. The bandwidth of an aerial for multichannel f.m. broadcasting has been improved by the use of folded slots. View full abstract»

39. The application of information theory to datatransmission systems, and the possible use of binary coding to increase channel capacity
Page(s): 291  302The simple application of information theory to data transmission shows that when the proper scaleunit of an input signal X(t) has been established by the reference of all noise to the input, the smallest timeinterval, ?t, in which one metron (i.e. a change of one scaleunit) must be transmitted is determined by the maximum possible rate of change of X(t); this determines the required bandwidth ?f ? 1/?t. Channel capacity is taken as the number of metrons that can be transmitted per unit bandwidth in unit time, and it is shown that, if provision is made for transmission of changes in X(t) at the maximum rate of one unit ?x in each basic interval of time ?t, there will be considerable waste of channel capacity, since, in general, the mean rate of change of X(t) will be much smaller than the maximum rate. It is shown that, provided a small delay for coding and decoding and some loss of fine structure in the received signal can be accepted, some of the time wasted, when X(t) is changing slowly, can be employed by integrating the changes in X(t) over a number of basic intervals ?t. The integrated change over the period ? = n?t can then be coded into binary form and transmitted during the following period while the current changes in X(t) are again being accumulated. In this way either the bandwidth can be reduced or the time saved can be used for transmission of other quantities, Y(t), Z(t), etc. It is shown that in this way the number of metrons transmitted can be increased by a factor M dependent on R, the ratio of the maximum rate of change to the mean rate of change without regard to sign, and n. There is some increase in the proper scaleunit, indicating some loss of accuracy, but M may have values of the order of 4 with an increase of proper scaleunit of less than 50%. It is then shown that in some cases provision is being made for transmission of more binary digits than are usually necessary, and by limiting the total change in X(t) that can be transmitted in  one period ?, a further saving can be effected with only a small increase in proper scaleunit when R is of the order of 10 or more. View full abstract»

40. On the optimum illumination taper for the objective of a microwave aerial
Page(s): 371  382The Fouriertransform description of the radiation pattern from an aperture is used to obtain curves relating the overall gain of an idealized aerial system, comprising an objective and waveguide flare, with the size and illumination of the aperture of the latter. For rectangular objectives the dimensions of the aperture of the flare may be varied independently in the two planes of symmetry and the overall gain obtained by multiplying together the gain factors for the distributions across the objective in these two planes. In the case of the circular objective this no longer applies, but curves are drawn showing the variation of the gain of the system as the size of a symmetrical feed is varied by equal amounts in the two planes of symmetry. It is shown that maximum overall gain is obtained with a rectangular objective when the size of the feed is adjusted to give a primary pattern such that the illumination intensity at the edges of the objective is 8Â¿ dB below that at the centre. The corresponding optimum taper for circular objectives is 11Â¿ dB. Primary radiationpatterns are drawn for Â¿constant,Â¿ Â¿cosineÂ¿ and Â¿doublecosineÂ¿ illuminations of the feed aperture. The variations of secondary beamwidths and first sidelobe levels with feed size for rectangular and circular objectives are discussed. View full abstract»

41. The Circuit Development of the Ampliphase Broadcasting Transmitter
Page(s): 391  399The paper describes the circuit design of a new type of broadcasting transmitter believed to be the most economical in equipment and valves and of the smallest dimensions and weight for a given power. It has an overall electrical efficiency and a modulation performance at least equal to that of the best known types. This latest type exploits phasemodulation internally in the transmitter to give a normal amplitudemodulated outputÂ¿hence the term Â¿ampliphase systemÂ¿Â¿amplitudemodulation derived from phasemodulation. View full abstract»

42. Attenuation in nickel and mildsteel waveguides at 9375 Mc/s
Page(s): 38  41Measurements of the attenuations produced by airfilled waveguides of nickel and mild steel have been made at a frequency of 9 375 Mc/s. It is shown that the permeability of a ferromagnetic material can be determined from such measurements provided the roughness of the waveguide internal surfaces can be estimated with reasonable certainty. It is found that mildsteel waveguides with machined internal surfaces give attenuations as high as 3.79 db/m, and the figure of 3 is deduced for the permeability of commerciallypurenickel drawn waveguide. View full abstract»

43. Basic groundwave propagation characteristics in the frequency band 50800 Mc/s
Page(s): 211  214The relation between existing experimental data on transmission at very high frequencies, at distances such that variations in atmospheric refractive index are of little significance, and fundamental propagation theory is discussed. An empirical correction for the difference between the field strengths observed over irregular terrain and theoretical values is given, and basic groundwave characteristics for the frequency band 50Â¿800 Mc/s are suggested which should be applicable except in very mountainous country or in densely builtup areas. Over this frequency band, and for distances inside the normal horizon, it appears that there is very little variation of median field strength with frequency for a given effective radiated power. View full abstract»

44. New Equipment for Impedance Matching and Measurement at Very High Frequencies
Page(s): 93  99The slotted transmission line has long been used as a standard device for determining impedance. Over the v.h.f. range, however, the constructional difficulties due to the physical length required for the slotted line make it primarily a laboratory instrument. The need for an alternative device of comparable or improved accuracy, capable of giving much more rapid measurements, and sufficiently robust to be used on field tests of aerial arrays, has led to a modified approach. A test section of lowloss coaxial line, which may be as short as onethird of the equivalent slotted line, is fitted with fixed probes to measure the relative voltage amplitudes at three known points. From these ratios the unknown impedance can be found, either analytically or graphically, each ratio defining a circular locus on the Smith chart. The frequency range covered by a line of this type is approximately 3:1; near midfrequency the present equipment can measure standingwave ratios up to 5:1, corresponding to resistive loads ranging from 15 to 375 ohms for a line of 75 ohms. An important advantage of the new equipment is that the adjustment of a load to a prescribed value is shown by the simultaneous zero reading of two meters. View full abstract»

45. A review of present knowledge of the ionospheric propagation of verylow, low and mediumfrequency waves
Page(s): 100  108The paper deals with the ionospheric propagation of waves of frequencies less than 3 Mc/s and is confined mainly to transmission over medium and long distances (greater than 500 km). The results of investigations on low and verylow frequencies (less than 300 kc/s) are summarized under the headings of field strength, phase and polarization measurement, the effects of ionospheric disturbances, the study of local ionospheric characteristics and theoretical studies. Since our knowledge of mediumfrequency propagation was adequately summarized in a report64 in 1937, only work done since that date has been considered here. An important item of the recent work is the study of ionospheric crossmodulation. The paper concludes with a summary of our present knowledge of the subject and recommendations for further studies. View full abstract»

46. Monotonic transient response
Page(s): 43  44First Page of the ArticleView full abstract» 
47. The application of power series to the solution of nonlinear circuit problems
Page(s): 453  475It is shown that Carson's power series solution of a triode circuit may be extended to the case in which the triode is associated with a linear network of any form. The reduction of nonlinear distortion in an amplifier by negative feedback is discussed. The conditions of stability for a triode circuit are derived, and it is shown that the solution remains convergent even when the circuit is regenerative, failing completely only at the point of critical regeneration. When the circuit is unstable and an e.m.f. near the natural frequency is applied, the solution represents an unstable oscillation, but, when the applied frequency is not near resonance, the solution will represent a stable forced oscillation if the amplitude is sufficiently large. View full abstract»

48. Directionfinding site errors at very high frequencies
Page(s): 321  332The paper summarizes theoretical and practical investigations into the cause and properties of site errors at metre wavelengths. Attention is mainly directed to Adcocktype aerial systems; but other classes of instrument are considered in an Appendix. A criterion is there suggested to express the susceptibility of a directionfinder to site error, and is applied to wellknown instrumental types. With some simplifying assumptions, the variations in error with azimuth and elevation angle due to Â¿pointÂ¿, Â¿linearÂ¿ and Â¿sheetÂ¿ type reflecting obstacles are examined. Certain properties of error charts which may be useful in locating the sources of error on a site are discussed. Errors introduced by randomly dispersed obstacles are considered from a statistical viewpoint. The theoretical and practical difficulties encountered in calibrating a site are discussed, the limitations of correction processes involving the use of previously measured error data being pointed out. Practical techniques available for locating the effective reflecting obstacles on a site are described, and examples of their application are given. Methods for suppressing unwanted reflections are considered. The work has led to a better understanding of site error phenomena at metre wavelengths, but further experimental work, linked with theoretical studies, is necessary. View full abstract»

49. The reflection and absorption of radio waves in the ionosphere
Page(s): 61  72A brief historical review is given of the investigations on the absorption of radio waves made in the United Kingdom since 1935 together with a detailed discussion of the factors which must be considered when making accurate measurements of this phenomenon. An outline of the theory of ionospheric absorption and its application to practical absorption measurements is included. The effects of double refraction, polarization, spatial attenuation, dispersion, ionospheric inhomogeneities and partial reflection, which modify the apparent attenuation of radio waves reflected in the ionosphere, are discussed. The methods used to minimize errors due to these factors are presented in detail. The experimental techniques used in the routine absorption measurements are described fully. The detailed results of the measurements of the absorption of radio waves in the ionosphere, conducted in SouthEast England during the years 1935 to 1948, are being published separately. View full abstract»

50. A WideAngle Microwave Radiator
Page(s): 255  258For many years it has been known that, in principle, optical lenses could have been made from nonhomogeneous glass. For example, if a glass sphere of unit radius were made with refractive index varying according to the relation. Â¿ = Â¿(2Â¿r2) where Â¿ = refractive index and r = radial distance from centre, it would act as a lens with the focus on the surface of the sphere. Such nonhomogeneous glass cannot be produced in practice; however, a microwave analogue has been constructed using spaced conducting sheets to produce a region of refractive index varying in accordance with the above relation. This lens, being circularly symmetrical, is free from aberrations as the feed is moved around the circumference, and is therefore suitable for wideangle scanning. It will operate only when the direction of polarization is such that the magnetic vector is normal to the conducting sheets. View full abstract»