摘要:

The paper presents investigations on the mutual impedance between two slots placed in close proximity. An analytical expression for the mutual impedance between two parallel longitudinal resonant slots in the broad wall of a rectangular waveguide is derived from the reaction of the magnetic field due to one of the slots, with the magnetic current exciting the other slot and with discontinuities in modal currents due to the two slots. The method of analysis is of general applicability. In the case under investigation, both slots are active, and a method for the experimental determination of mutual impedance between two active slots is presented. The values of mutual impedance computed from the theoretical formula are in good agreement with those obtained experimentally.

DOI:10.1049/piee.1971.0281

出版商:IEE    

年代:1971

数据来源: IET

摘要:

An expression is derived for the radiation pattern of a hybrid-mode field distributed over a circular aperture. The hybrid mode consists of a combination of TMmand TEmcomponents (wherem≥ 1) and is the type of wave which propagates in a cylindrical waveguide with an internal lossless anisotropic surface. The requirements for pattern symmetry and linear polarisation are then derived, and the form of the radiation pattern when the waveguide boundary consists of either circumferential or longitudinal slots is discussed. The advantages of using hybrid modes, instead of TM and TE modes, in a smooth pipe for optimising the performance of a paraboloid are considered. The principle of synthetising a desired paraboloid-aperture distribution by the superposition of the beams radiating from a hybrid-mode feed at the prime focus is discussed. The parameters of the hybrid modes in the waveguide, and its diameter, are optimised to obtain maximum aperture efficiency for a given number of modes by a field-matching technique at the feed aperture. Efficiencies for feeds supporting up to five hybrid modes are calculated for a paraboloid semiangle of 63°. These values are compared with those derived by field matching over the paraboloid aperture. The procedure for optimising the figure of merit of 1- and 2-hybrid-mode feeds is then considered, together with the effect of changing the mode-power ratio in the case of the 2-mode feed. Finally, the effect of frequency on the aperture efficiency and figure of merit of the 1- and 2-mode feeds is discussed.

DOI:10.1049/piee.1971.0282

出版商:IEE    

年代:1971

数据来源: IET

摘要:

An expression for the directivity of a short backfire antenna has been derived in terms of the reflection coefficient of the plane conductor. The analysis considers only the series of images behind the surface-wave reflector and the dipole feed. Using this expression, the directivity is calculated and compared with the experimentally obtained directivity. The gain was measured in the laboratory by the standard method, using microwave-absorbing material to reduce the effect of unwanted reflections from the floor, ceiling etc.

DOI:10.1049/piee.1971.0283

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The available experimental data relating to the height distribution of electron concentration at night has shown the presence of a pronounced ledge of ionisation between about 80 and 90km, and thin layers at greater heights. Idealised models of the electron-density distribution have been constructed, some of which incorporate these two features. The propagation parameters for vertically polarised radiowaves, in the frequency range 4–1000kHz, incident on these models, have been computed using a full-wave integration procedure. These computations have been carried out for angles of incidence of 30° and 80°, at various azimuths, and for middle and low latitudes. Particular attention is paid to the polarisation conditions of the reflected waves, and special emphasis is given to the results for frequencies near 10 and 100kHz, of interest for radio navigational aids, and near 300kHz, which are important for broadcasting.

DOI:10.1049/piee.1971.0284

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The design of an instrument for rapidly measuring the changes in the profile of large steerable radio reflectors is described. Its use is illustrated by measurements of the reflector deformation of the UK Science Research Council's 25m steerable aerial at Chilbolton, Hants., England, as the aerial is tilted and accelerated. The laser instrument surveys 36 points distributed on the reflector in 3s, and the overall accuracy of measurement as installed on the aerial is estimated to be within ±0.4mm(r.m.s.), with a repetition error of 0.2mm(r.m.s.). Lower figures should be achievable with smaller aerials.

DOI:10.1049/piee.1971.0285

出版商:IEE    

年代:1971

数据来源: IET

摘要:

A calculation of network sensitivity is presented. In particular, it is shown that the first, higher and mixed-higher derivatives may be calculated with computational ease. The results are shown to provide a solution to the problems of repeated network analysis in which only a few network parameters are varying from analysis to analysis. The reduced computing effort involved compared with conventional methods is of particular importance in application to ‘iterative synthesis’ techniques.

DOI:10.1049/piee.1971.0286

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The paper describes a new form of linear reluctance motor capable of operating over displacements of 1 m or more with good positional accuracy and at a relatively low speed. The main application of the motor is as a linear actuator for precise machine-tool operations. The principle of operation and the main design factors of the motor are described, together with a theoretical assessment of performance. Experimental results obtained on two prototype machines are given, and are shown to compare favourably with the theoretical analysis.

DOI:10.1049/piee.1971.0288

出版商:IEE    

年代:1971

数据来源: IET

摘要:

In this paper two methods, a graphoanalytical method and an approximate analytical method, are presented for the analysis of the d.c. dynamic braking of an induction motor with a saturistor in its rotor circuit. Both these methods take into account the saturation of the magnetic circuit of the motor and the nonlinear nature of the resistance/current and reactance/current characteristics of the saturistor, and allow fairly accurate prediction of speed/torque and speed/current characteristics. The conditions for maximum torque, with given values of stator excitation and magnetising current, have been derived. The nature of speed/torque and speed/current characteristics for different values of stator excitation, different numbers of turns in the saturistor, different resistances in series with the saturistor in the rotor circuit and with d.c. control of the saturistor has been discussed. It is shown that the braking performance with an optimum resistance in series with the saturistor is superior to that when either the resistance, the saturistor or both are omitted.

DOI:10.1049/piee.1971.0289

出版商:IEE    

年代:1971

数据来源: IET

摘要:

A novel type of a.c. machine is described which has an asynchronous mode of operation but which does not rely on induced currents or losses in the rotor. It has a polyphase stator winding and a laminated rotor with ‘directional’ magnetic properties, and thus closely resembles a reluctance motor. In contrast to the reluctance motor, however, two rotating main fields are produced, and the machine is self starting (without a cage winding) and runs up to a speed which is inversely proportional to the sum of the two pole numbers. It may also be run synchronously by doubly feeding the stator winding with alternating and direct current. The machine is basically a low-speed device. On theoretical grounds, it was expected to have an asynchronous performance comparable with that of a conventional squirrel-cage induction motor, but this has not been borne out in practice. It is shown, however, that there is scope for further development by making use of an axially laminated form of rotor construction.

DOI:10.1049/piee.1971.0290

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The paper is a contribution to the transient-stability study of multimachine power systems by Lyapunov's direct method. The mathematical model used is more rigorous than those already taken into account in that the machines' inertia coefficients are no longer considered as constant but varying with angular speed. This constitutes a more accurate approach to the transient-stability problem. A 9-machine realistic power system illustrates the proposed method, and permits comparisons and conclusions to be made.

DOI:10.1049/piee.1971.0291

出版商:IEE    

年代:1971

数据来源: IET