摘要:

Scattering from a cylindrical metallic object placed centrally in a waveguide so that its axis is parallel to the transverse magnetic field of the dominant mode is shown to give rise to two field types in the scattered waves, which are dipole and isotropic in nature. On the other hand, a dielectric rod similarly placed shows only dipole scattering. A method is presented which uses a potential theory to describe dipole scattering from metallic, dielectric and magnetic obstacles, and it is further shown that the theory may be used to derive in a simple manner the dipole scattering from a coaxial obstacle which may consist of a metal rod with a dielectric or magnetic sleeve, or coaxial combinations of dielectric and magnetic materials.Isotropic scattering is important in a coaxial system only when the core is a good conductor, and it is shown by an electromagnetic solution that its magnitude is associated only with the radius of the metal core, any dielectric outer sleeve having negligible effect, provided that the overall radius is sufficiently small.

DOI:10.1049/piee.1963.0244

出版商:IEE    

年代:1963

数据来源: IET

摘要:

A radio wave after reflection from the ionosphere is considered to consist of a specularly reflected component plus a varying diffracted component. The ratio of the power in the specular component to that in the diffracted component is of interest in considering the design and performance of large-aperture receiving arrays. A theoretical treatment is presented whereby this ratio can be derived from the probability distribution of the phase difference between the signals received at two widely spaced aerials. Apparatus for the determination of the phase-difference distribution is described, and the experimental technique developed for using the apparatus is discussed.The results of measurements made on typical h.f. transmissions are presented and discussed in relation to known ionospheric phenomena. Consideration is also given to the use of the techniques for the determination of the vertical arrival angle and the angular spread of the cone of radiation of a received signal.

DOI:10.1049/piee.1963.0245

出版商:IEE    

年代:1963

数据来源: IET

摘要:

The paper summarizes the fundamental limitations set by the available light and the efficiency of the photocathodes available at present, and considers in detail how closely existing types of camera tube and image intensifier can approach this fundamental limit. There are many possibilities, from the simple adaptation of existing broadcast tubes to the combination of high-gain image intensifiers with conventional television camera tubes, either by optic or fibre optic coupling or by building the two into the same vacuum envelope. Between these, one may say that the problems of low-light-level television are well on the way to being solved within the limits set by the factors already referred to.

DOI:10.1049/piee.1963.0246

出版商:IEE    

年代:1963

数据来源: IET

摘要:

Probes in which the usual connecting leads to the detector have been eliminated have been constructed for measuring the intensity of an electromagnetic field. The new devices are modulated reradiating or scattering antennas that consist of either a small dipole (for measuring the electric field) or a small shielded loop (for measuring the magnetic field) centre-loaded with a photocell illuminated by a chopped beam of light. The modulated scattered signal from the probe is proportional either to the component of the E-field which is parallel to the axis of the dipole, or to the component of the H-field which is perpendicular to the plane of the shielded loop. The scattered signal is received by an additional antenna or by the same antenna as is used for transmission. The received signal is amplified by a lock-in amplifier.The same principle has also been applied to the measurement of the distribution of current along an antenna of arbitrary shape. This was accomplished by sliding a small shielded-loop probe, centre-loaded with a photocell, along the antenna. A very small and constant gap was maintained between the probe and the antenna. The modulation factor of the scattered signal was determined from the measured instantaneous impedance of the photocell.Both the near-field pattern of a λ/2 dipole antenna and the distribution of current along the antenna as measured with these optical probes are in general agreement with theory. The properties of several other types of probes based on the same principle were also explored.

DOI:10.1049/piee.1963.0247

出版商:IEE    

年代:1963

数据来源: IET

摘要:

An arrangement of isotropic elements, uniformly spaced at a half wavelength or greater and suitably excited, was used by Dolph to obtain optimum radiation patterns for linear broadside arrays. Riblet generalized the technique and extended it to include arrays of odd numbers of elements with uniform spacing of less than a half wavelength. DuHamel demonstrated that the calculation of the excitation coefficients for an array of 2n+ 1 elements is equivalent to that of determining the coefficientsbmin the expressionTn(ax+ b) = Σm=0nbmTm(x) (n > 0),whereTm(X) = cos (mcos−1x), |x|≤ 1,m≥ 0, andaandbare constants. An expression of simpler and more convenient form than that of DuHamel's formulae has been provided by Salzer, and rederived rather simply by Brown. It is the purpose of the paper to present two alternative formulae forbm. The first is recursive, consisting of a single summation with coefficients involving the sum of only two binomial coefficients, and of simpler form than that of Salzer. The second, also a single summation of reasonably simple quantities, is similar to a recently announced formulation by Brown, except that all the coefficientsbmare obtainable from the one expression.

DOI:10.1049/piee.1963.0248

出版商:IEE    

年代:1963

数据来源: IET

摘要:

A form of the microwave reflectometer which yields a reflection-coefficient angle as well as modulus is discussed and its analysis presented.A simple compensation method is described whereby the measurement errors due to imperfect performance of the directional couplers can partially be eliminated and partially be allowed for.Finally, the measurement accuracy obtainable from this reflectometer system is shown to be approximately that obtainable from the conventional slotted waveguide section, and hence the system provides an alternative to the slotted section at the millimetre wavelengths.

DOI:10.1049/piee.1963.0249

出版商:IEE    

年代:1963

数据来源: IET

摘要:

TaperedRCtransmission lines are useful in phase-shift oscillators, because they permit (i) a great reduction in the required gain of the active device (vacuum tube or transistor) and (ii) generation of frequencies up to a few megacycles per second. They are particularly useful for microminiature oscillator circuits because of their small size and the possibility of integration with the active device, which is a transistor. In the paper, a general, exponentially taperedRCline is analysed to find expressions for the current and voltage at any point of the line. These are used to deduce an equation giving the frequency of phase reversal and an expression for the attenuation at this frequency, for the possible combinations of generator and load impedances that are of practical interest. In general, the frequency-determining equation is transcendental and highly involved. An approximation is developed in the paper for small-taper parameters; using this approximation, it has been shown that, for a particular frequency, there exists an optimum combination of load impedance and taper parameter for which the attenuation is a minimum.Each special case is illustrated by a numerical example, and the results are verified by experiment.

DOI:10.1049/piee.1963.0250

出版商:IEE    

年代:1963

数据来源: IET

摘要:

The paper describes the sources and components of stray load losses in squirrel-cage induction motors and examines the validity of the reverse-rotation test method which has previously been recommended as the best available method for measuring the loss.It is shown that this method of test is based on assumptions which are fundamentally incorrect, and that the consequent errors in measured loss will be small only if the slot harmonics produce the major proportion of the total high-frequency stray loss. In other cases, with the particular design features detailed in the paper, the discrepancies can be significant.It is concluded that the validity of the test when applied to large motors is open to some doubt.

DOI:10.1049/piee.1963.0253

出版商:IEE    

年代:1963

数据来源: IET

摘要:

The mode theory approach is shown to lead to a complete solution of problems involving machine systems under the normal assumptions necessary to give linear differential equations. Only two basic matrix operations, namely inversion and latent root evaluation, suffice to enable determination of the response to any input applied at any set of terminals.It is shown that there are four distinct types of input for a multi-variate system and in some cases superposition does not apply. The effects of open- and short-circuits and of changes in the circuit parameters are analysed in terms of this classification.An indication is given of how the constants of a system may be evaluated if the modes are known.

DOI:10.1049/piee.1963.0255

出版商:IEE    

年代:1963

数据来源: IET

DOI:10.1049/piee.1963.0259

出版商:IEE    

年代:1963

数据来源: IET