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Computer prediction of RCS for military targets ... - IEEE Xplore

Computer prediction of RCS for military targets ... - IEEE Xplore

Computer prediction of RCS for military targets ... - IEEE

Computer prediction of RCS for military targets P.A. Lees, MA M.R. Davies, BSc, DPhil Indexing terms: Radar cross-section, Computer simulation. Abstract: There are a number of well established theoretical techniques for predicting the local scat- tering of high-frequency electromagnetic radiation, including physical optics (PO), the geometrical theory of diffraction (GTD), and developments and refinements of these. The paper discusses means of integrating local scattering theories such as these into a global system able to predict and analyse the radar cross-section of large, complex targets defined by a digital database. In particular, a computer system developed for the RCS predic- tion of military platforms, which uses ray-tracing methods to perform this integration, is described. The approach used in this system aims to maxi- mise predictive power by making the greatest use of the target description itself in estimating its RCS, avoiding reliance on subjective assessment by the user or the need for empirical parameters. This work is used to illustrate the benefits and problems inherent in this approach. 1 Introduction Prediction of the radar cross-section (RCS) of military targets is of enormous operational significance because of the importance of radar sensors in all types and phases of military engagements. The ability to predict the radar signature of a given configuration and to understand the sources of prominent returns is a necessary part of signa- ture control and reduction, whether at the design stage or for remedial measures to existing targets. More generally, a detailed understanding of the scattered electromagnetic field is increasingly important in the light of modern weapons, which exploit features such as polarisation and statistical characteristics for target discrimination or per- formance enhancement. Despite this importance, and the availability of high-speed computing and of well estab- lished electromagnetic scattering formulations, practical and accurate RCS prediction for targets such as ships, land vehicles, aircraft and missiles, or fixed installations, is still in its infancy. In this paper, we consider possible computer-based solutions to the RCS prediction problem in the asymp- totic high-frequency, or quasioptical, regime, where the radar wavelength is small in terms of the characteristic dimensions of the target. For targets such as the above, this will usually encompass the operationally important Paper 7336F (El$ first received 26th October 1989 and in revised form 11th April 1990 The authors are wlth SD Europe Ltd., 49 krners Street, London WlP 4AQ, United Kingdom IEE PROCEEDINGS, Vol. 137, Pt. F. No. 4, AUGUST 1990 centimetric and millimetric radar cases (D/E-band and higher). In this regime, the sheer geometrical complexity of these targets and the interactions between the different elements of their structure is probably the main source of difficulty in the development of effective signature predic- tion. As we shall describe below, there are a number of pos- sible approaches for computer-based aids to RCS predic- tion. The main part of this paper describes an approach which has been followed in a computer system developed by SD Europe Ltd. (previously Scicon Ltd.), and we use this to illustrate some of the advantages and problems inherent in this philosophy. 2 Approaches to high-frequency RCS prediction Estimation of the RCS of military targets is based on three techniques, all of which have their merits and demerits for particular aspects of RCS prediction: experi- mental measurement of real, full-scale targets; experimen- tal measurement of specially prepared scale models; and theoretical prediction, with which this paper is con- cerned. Traditionally, nonexperimental RCS prediction of real targets would be based on detailed inspection of the target geometry by an experienced analyst, who would use comparison with similar known targets, identification of features likely to give rise to high returns, and quanti- tative analysis of the latter. This type of expert assess- ment will also continue to form part of the RCS prediction armoury. With modern computational tech- niques, however, a properly automated and systematic approach to theoretical prediction is possible. We now turn to current approaches to computer-based RCS pre- diction for the asymptotic high-frequency rtgime. A key feature of electromagnetic scattering in the high- frequency limit is the localised nature of the phenome- non. This makes it possible to divide the direct scattering problem for a large target into two more or less distinct parts: a local problem of how the incident and scattered fields are related at a particular point on the target; and a global problem, concerned with the interaction and combination of the scattered-field contributions from different points of the target. This view would not be pos- sible, for instance, with resonant scattering where the field is coupled to the target in a manner dependent on its global structure and dimensions. For local scattering calculations, all current RCS pre- diction techniques are based on a range of well estab- lished asymptotic formulations of electromagnetic scattering [ 11 : formulations based on ray optics, includ- ing geometrical optics (GO), the geometrical theory of diffraction (GTD), and developments of GTD, notably 229

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