摘要:

Binary plot extraction systems are used in contemporary radar systems as an economical means for providing information on the presence and position of targets, by combining data from all the pulses during one scan of the beam. The paper assesses the performance of two binary plot extraction systems employing digital integrating counters. It is shown how to obtain probability of detection curves for constant point targets and point targets exhibiting scan-to-scan or pulse-to-pulse fading. The measurement of azimuth is also discussed and the error involved is evaluated.

DOI:10.1049/piee.1974.0281

出版商:IEE    

年代:1974

数据来源: IET

摘要:

Normalised series-expansion coefficients are presented for the numerical design of the surfaces of extremely short-focal-length/wide angle asperical scanning lens antennas with symmetrical off-axis focal points. Based on theoretical techniques previously developed for the problem, the normalised numerical results presented assume an index of refraction of 1.594 and a fixed off-axis angle of 20° for design purposes. Included also are curves of certain related design parameters, and information on lens-antenna performance characteristics in the form of typical scanning diffraction patterns for radiation or reception. Some worked examples are given.

DOI:10.1049/piee.1974.0282

出版商:IEE    

年代:1974

数据来源: IET

摘要:

A closed loop antenna being driven through a straight ‘centre line’ conductor which bridges the loop at an axis of the symmetry has been considered. This antenna is called the ‘centre-line-driven loop antenna’. In view of the circuit and radiation properties, this is considered as two closely coupled coplanar loops, compressed into a single loop. By approximation of the antenna current by interpolation polynomials, Hallen's integral equations for this antenna current have been solved by the numerical method, utilising a high-speed computer. The circuit and radiation properties of this antenna are investigated experimentally and numerically. The wideband properties in the radiation pattern and directivity are noteworthy. The most likely applications for this antenna are receiving and transmitting antennas for u.h.f. broadcasting.

DOI:10.1049/piee.1974.0283

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The nature of an equivalent network of slots having any arbitrary orientation in the broad wall of a rectangular waveguide, for both even and odd distributions of the aperture field, has been investigated. The complex power radiated by the slot has been determined from the angular spectrum of plane waves. The impedance characteristics of the transverse slot and of the centred inclined slot have been obtained from the complex radiated power and the discontinuity in the modal voltage, as well as from the scattering coefficients, using the energy balance equation. The impedance characteristics calculated by the two methods are identical. The theoretical results are in good agreement with experimental results.

DOI:10.1049/piee.1974.0284

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The paper describes experimental evidence, supported by a simple theoretical analysis, of a new form of wave inside a rectangular-guide structure, two opposite walls of which present to the field anisotropic impedances. The mode concerned is of dipole pattern, belonging to the surface-wave family, and is not subject to cutoff. It is shown to be a slow wave, and to propagate along a guide of cross-sectional dimensions that are insufficient to provide for the support of any of the so-called waveguide modes. In the case considered, two walls of the guide facing each other consist of grids of spaced parallel wires running in the direction of propagation, while the other two surfaces comprise the usual continuous bare metal plates. The distinctive feature of the electromagnetic field over the transverse plane within this structure is its wave character between the opposite smooth metal walls, and its highly evanescent behaviour in the perpendicular direction. The spacing between adjacent conductors of the wire-grid surfaces is shown to affect the velocity of propagation of the wave along the guide, and the attenuation is found to be of the same order as that of TEM wave at the corresponding frequency. There are, in fact, prospects of reduced transmission losses at high frequencies using this dipole-type mode, which may be regarded as a perturbed TEM wave transforming more closely to that pattern as the frequency is reduced.

DOI:10.1049/piee.1974.0285

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The interface between empty and dielectric-loaded lossless waveguides is discussed in terms of three independent measurable quantities. A mode-matching technique is used to obtain an equivalent-circuit representation of the junction, when only the dominant mode propagates in each waveguide. The circuit has the form of two equivalent transmission lines, which describe the two waveguides, and a 2-element network, which describes the effect of the interface. It is shown that this is the only meaningful and useful representation, and that a unique value of the normalised equivalent characteristic admittance of the inhomogeneous waveguide can thus be determined for any loading configuration. This admittance is shown to be not generally proportional to the wave admittance, even when the latter can be defined. In most practical situations, where only one mode may propagate in each waveguide, the effect of the interface can be neglected and matching can be achieved on the basis of this characteristic admittance alone. Computed values of the normalised equivalent-circuit elements and characteristic admittances are given for both E-plane and H-plane loading over a wide range of parameters.

DOI:10.1049/piee.1974.0286

出版商:IEE    

年代:1974

数据来源: IET

摘要:

Theoretical and simulation results are presented for the overheads in packet-switched networks. These overheads arise owing to the operational spects of the network and ‘blank’ padding of the last packet of a message. Message lengths have been assumed to be exponentially distributed. Results indicate good agreement between theoretical and simulation results. It is concluded that overheads can be reduced in this case if the ratio of mean message length to packet length is kept high. In such cases, it is also possible to find an optimum packet size such that the combined overheads are minimised, under certain restrictions.

DOI:10.1049/piee.1974.0287

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The problem of determining fault position on a series-compensated power line is considered and a novel measuring scheme based on definite integrals of relaying current and voltage is described. Attention is given to the effect of travelling-wave distortion of relaying signals in designing a prototype single-phase relay. Details of the equipment construction are given together with laboratory tests on a lumpedparameter line model and digital-computer simulated tests on a distributed-parameter line model.

DOI:10.1049/piee.1974.0288

出版商:IEE    

年代:1974

数据来源: IET

摘要:

In the last decade or more, a number of tests on large synchronous machines and the associated analytical work have revealed certain inaccuracies in the theory of synchronous-machine performance, which has been used for the last half century. A new look is taken at the assumptions underlying the old theory and several of them are discarded in the derivation of a new theory which corrects many of the inaccuracies. The new theory results in new formulas for the calculation of machine parameters, such as transient reactance and transient time constant; it is particularly relevant in the calculation of parameters for synchronous machines with damper windings.

DOI:10.1049/piee.1974.0289

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The linear induction machine is considered as a stack of rectangular regions bounded by an impressed excitation. These regions may in general be moving or stationary secondary conductors and iron segments and airgaps. For performance analysis, the field quantities must be evaluated in each region. A wave-impedance approach has previously been successfully applied in cases where lateral edge effects are neglected. Its application greatly simplifies the tedious task of matching up boundary conditions. The paper outlines a wave-impedance approach that takes into account the finite width of the secondary. Consequently the effects of the closure of the induced currents as well as skin effect can be simultaneously studied. The generalised results are shown to give answers consistent with known formulas when in turn lateral and skin effect are neglected.

DOI:10.1049/piee.1974.0290

出版商:IEE    

年代:1974

数据来源: IET