Abstract
A generalized electromagnetic model is presented in order to predict the response of forward scatter radar (FSR) systems for air-target surveillance applications in both far-field and near-field conditions. The relevant scattering problem is tackled by developing the Helmholtz–Kirchhoff formula and Babinet’s principle to express the scattered and the total fields in typical FSR configurations. To fix the distinctive features of this class of problems, our approach is applied here to metallic targets with canonical rectangular shapes illuminated by a plane wave, but the model can straightforwardly be used to account for more general scenarios. By exploiting suitable approximations, a simple analytical formulation is derived allowing us to efficiently describe the characteristics of the FSR response for a target transitioning with respect to the receiver from far-field to near-field regions. The effects of different target electrical sizes and detection distances on the received signal, as well as the impact of the trajectory of the moving object, are evaluated and discussed. All of the results are shown in terms of quantities normalized to the wavelength and can be generalized to different configurations once the carrier frequency of the FSR system is set. The range of validity of the proposed closed-form approach has been checked by means of numerical analyses, involving comparisons also with a customized implementation of a full-wave commercial CAD tool. The outcomes of this study can pave the way for significant extensions on the applicability of the FSR technique.
Highlights
The detection of objects with reduced radar cross-section (RCS) is one of the most challenging problems for air-target surveillance applications
The physical explanation of the phenomenon can be derived through the well-known Babinet’s principle (BP) [27,28,29]; by applying the equivalence theorem, if the target is replaced with its silhouette, the induced currents on the target must be equal to the surface current on an infinite plane [7,35]
Since forward scatter radar (FSR) systems are able to provide an enhanced detection capability that can be very effective for the monitoring of unmanned aerial vehicles (UAVs) and low-observable targets, a comprehensive electromagnetic model has been presented in this work for the characterization of the forward scattering generated by two-dimensional shapes, useful when the receiver is either in far-field and in near-field with respect to the target illuminated by a plane wave
Summary
The detection of objects with reduced radar cross-section (RCS) is one of the most challenging problems for air-target surveillance applications. Due to an ever-increasing diffusion of unmanned aerial vehicles (UAVs), in particular drones, air-traffic systems capable of providing reliable surveillance and avoiding violation of no-fly zones look highly desirable. The traffic control of city airspace is crucial for population safety. UAVs are typical examples of low-signature targets that may result in being practically invisible to common monostatic or bistatic radar systems [1,2]. Objects having a small size and made of particular materials exhibit a reduced cross-section; this happens to big-sized targets of special shapes having the capability of redirecting the electromagnetic (EM) waves in different directions with respect to the illuminating antenna.
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