DOI:10.1049/ree.1977.0001

出版商:IERE    

年代:1977

数据来源: IET

摘要:

Fixed circular polarization has been used for rain clutter reduction for over thirty years,1–3but a proper understanding of the inter-relationship of radar propagation path and target parameters is still not widely known. The paper sets out to provide a basic analysis, together with a set of ‘universal curves’ from which expected rain clutter reduction and target loss may be obtained for any particular set of circumstances.The paper then provides a guide to current literature from which the nearest reported results may be used to provide realistic performance estimates. These are supported with a limited number of experimental results obtained with an X-band radar fitted with dual aerials.Comments on the use of the propagation factorFfor rain in the special case of surface search radars are offered for criticism.An alternative method of rain rejection using orthogonal linear polarization for transmission and reception is also covered in less detail.

DOI:10.1049/ree.1977.0002

出版商:IERE    

年代:1977

数据来源: IET

摘要:

A method of generating a single sharp null response in an otherwise omni-directional pattern using a circular array is discussed. The null width is reduced by the introduction of an abrupt phase reversal in the pattern function in the direction of the null. The null is also electronically steerable in the azimuth and in the elevation plane. Mutual coupling effect on the depth of the null is minimized through the use of sequence excitation components in the feed.

DOI:10.1049/ree.1977.0003

出版商:IERE    

年代:1977

数据来源: IET

摘要:

Picture recognition and analysis has numerous applications in all fields of technology, from medical diagnosis to document processing. This paper introduces some of the basic techniques of picture analysis:correlation, or matching of pictures;transformationsand their uses, including their application tonormalizationfor recognition purposes;parametrization, or property measurement, for picture classification; andsegmentationof a picture into parts for purposes of description, with emphasis on segmentation based on regionconnectivity. Examples are given showing how each of these techniques is important in practical applications.

DOI:10.1049/ree.1977.0004

出版商:IERE    

年代:1977

数据来源: IET

摘要:

This paper reviews the basic physical principles behind:the processing and combination of noisy signals;the quantification of information and of channel capacity;transformations and dualities in the representation of signals in frequency, time and space.The treatment is largely non-mathematical, and is aimed at fostering an insight into the nature of these concepts and their interrelations. In each of its three parts, the paper outlines some of the basic principles and theorems, indicates—and in some instances extends—the limits of their application, and then relates them to real-life operating conditions and design objectives. It is hoped that this approach will assist readers to see the connection between systems they are analysing, assessing or designing, and the idealized models normally postulated for the development of formal theoretical methods.Special emphasis is given to ways of looking at signal design and processing problems which have proved of particular value in system development in a wide field of applications.

DOI:10.1049/ree.1977.0005

出版商:IERE    

年代:1977

数据来源: IET

摘要:

Digital signal processing offers considerable advantages over analogue processing for video target extraction in moving target indication (m.t.i.) radars. These advantages include simplicity in the realization of delays, overall stability of the processor and the possibility of multiplexing. However, because of the finite resolution of the arithmetic unit, digital processing introduces a noise component which is a function of the resolution (register length), mode of arithmetic and filter configuration.A theoretical and experimental evaluation of six representative digital filters, suitable for m.t.i. systems, is presented which shows that the simple model of round-off noise is a good approximation of the round-off process and good agreement is obtained between the theoretical and experimental estimates. The model partially fails in the case of recursive filters, because these filters do not satisfy the basic assumptions of the model.

DOI:10.1049/ree.1977.0006

出版商:IERE    

年代:1977

数据来源: IET

摘要:

A ‘long loop’ v.h.f. phase-locked a.m. receiver with synchronous detector is described. The effect of the narrow-band Chebyshev i.f. filter on receiver lock-in range, hold-in range and capture time is investigated as a function of carrier level, −60 to −120 dBV, for a range of low-pass filter time-constants. The transient response of the Chebyshev filter and instantaneous limiting in the i.f. strip are shown to play a crucial role in determining the time which the receiver takes to lock onto the carrier. The receiver is not significantly more complex or expensive than sets currently in use and has the advantage that it may also be used to demodulate double-sideband diminished carrier (d.s.b.d.c.) signals.

DOI:10.1049/ree.1977.0008

出版商:IERE    

年代:1977

数据来源: IET