摘要:

An X-band radar with back-to-back horizontally and vertically polarized antennas of equal gain and beamwidths was built. The antennas were enclosed in a symmetrical aerodynamic radome permitting speeds of rotation from 20 rev/min to 600 rev/min. The radar power was switched every half revolution from one antenna to the other, so that a sea-clutter picture presented on the top 180° of the p.p.i. display was identically repeated on the lower 180°, but with the orthogonal polarization. Some of the different characteristics of sea-clutter on the two polarizations were strikingly illustrated by this virtually simultaneous presentation. The sea-clutter smoothing effects obtained by decorrelation and integration are demonstrated. The r.m.s. sea-clutter amplitude was brought down to that of the noise by a true i.f. (amplifying logarithmically at the input frequency) type of constant false alarm rate (c.f.a.r.) receiver developed during this work. Recent work on logarithmic receivers has shown that the output noise fluctuations do not always become constant and independent of input r.m.s. noise amplitude, even though a near perfect logarithmic input-output law may be obtained on pulse or continuous wave (c.w.) inputs. The performance of the true i.f. logarithmic amplifier has been investigated using a wide-band noise source (the output of which may be varied through 50 dB) to feed the amplifier. The conditions which must be observed if the output noise fluctuations are to remain constant while the input noise varies over this range have been established. When these conditions are met there is no significant impairment of detectability of weak signals against noise when using a logarithmic receiver, compared with a linear receiver.

DOI:10.1049/ree.1969.0097

出版商:IERE    

年代:1969

数据来源: IET

摘要:

Workers in the field of colour television broadcasting may find some of the contents of this paper interesting or provocative. The working party has been very conscious all along that many of the figures quoted were open to question either because of lack of solid information or because of differences in techniques and practices, and would therefore welcome comment and contribution. Comments should be sent to the Technical Secretary of the British Radio Equipment Manufacturers' Association.

DOI:10.1049/ree.1969.0102

出版商:IERE    

年代:1969

数据来源: IET

摘要:

A finite-element method based on a function minimization techinique is developed for analyzing homogeneous waveguide problems. The continuous eigen-value operator as in the Ritz finite-difference method is replaced by a matrix operator. The resulting equations are, however, matrix eigen-value equations. Relevant properties of the matrices are discussed. It is demonstrated that the method has advantages in dealing with awkward boundaries and singularities. A feature of the method is that the error in the eigen-value is a monotonically decreasing function of successive sub-divisions of the cross-section. Minimization of a variational expression assures rapid convergence to the correct eigen-value. Three waveguides are analysed in some detail.

DOI:10.1049/ree.1969.0103

出版商:IERE    

年代:1969

数据来源: IET

摘要:

If the fundamental consideration of domain size were the dominant factor, it would theoretically be possible to store information on magnetic disks with a packing density of at least 1010bits per square inch.To be of practical use, the fundamental design limits of the data channel and its components, the practical magnetic design of the media and recording heads, the mechanical tolerances and wear properties of the entire combination of medium, head and transports, have to be considered. Under practical conditions, current files operate at a density of 2 × 105bit per square inch.This paper reviews the overall interaction of these limiting parameters, and discusses some of them in detail.

DOI:10.1049/ree.1969.0104

出版商:IERE    

年代:1969

数据来源: IET

摘要:

A method for the determination of optimum transfer functions for systems controlling plant with input saturation is presented. The procedure is demonstrated on a specific plant well studied in the literature, and the general conclusions verified by simulator and digital computer results. It is established that the desired system bandwidth should be obtained with a dominant system transfer function of low Π| system poles| /Π |system zeros|. The order of the dominant system transfer function is usually physically obvious from the asymptotic Bode plot, and as in modern control theory, the Butterworth array is found to be particularly useful. Provided the right order of transfer function is chosen, the actual pole-zero geometry is not critical. Such a design is optimal with regard to small transient excursions into the non-linear mode, and with regard to the minimization of noise effects on the plant input level, yet simultaneously meets the customary deterministic performance criteria.In the comparison of series compensation designs, it is shown experimentally that some marginal reduction of sensitivity is achieved by reducing the order of the dominant transfer function, but this reduction is easily offset by the use of feedback compensation. Far-off poles added to filter high frequency noise are found to have little effect on the choice of optimum transfer function. Velocity constant requirements are met by the addition of integrating dipoles. A useful theorem providing a quantitative measure of the deterioration in non-linear performance caused by the choice of excessive bandwidth is presented and is shown to result in a power law.By expressing the conclusions as s plane constraints for the dominant poles and zeros, the results can be easily incorporated in any standard design procedure, manual or automated, and should lead to considerable reduction in the time required to obtain a satisfactory design.

DOI:10.1049/ree.1969.0105

出版商:IERE    

年代:1969

数据来源: IET