Janic Chauveau

Selection of Contributing Natural Poles for the Characterization of Perfectly Conducting Targets in Resonance Region

In the resonance region, the radar scattering response of any target can be modeled by natural poles, with the formalism of the singularity expansion method. The mapping of poles gives useful information for the discrimination of radar targets. In this paper, we show that a reduced number of natural poles is sufficient to characterize such objects. Furthermore, we propose a procedure for selecting the poles that actually contribute to the scattering response. Results are presented for various perfectly conducting (PC) canonical targets and for a PC complex shape target.

Determination of resonance poles of radar targets in narrow frequency bands

In resonance domain, the radar scattering response of any object can be modelled by natural poles of resonance with the formalism of the singularity expansion method. The mapping of these poles in the complex plane gives useful information for the discrimination of a radar target, as its general shape, its characteristic dimension and its constitution. However, the full frequency band corresponding to the resonance domain of a radar target is not always available, thus it is often necessary to look for a compromise. In this paper, we propose to show that it is possible to extract resonance poles one-by-one in tuning a reduced frequency band to the frequency of each wanted pole. This avoids the use of ultra wide band (UWB) data and allows to extract at least some dominant poles of resonance in available narrow frequency bands.

Accuracy of Singularity Expansion Method in Time and Frequency Domains to Characterize Antennas in Presence of Noise

In this paper, the accuracy of the singularity expansion method (SEM) used for antenna characterization is investigated. A well-known limitation of the SEM is that pole extraction is very sensitive to noise. A comparison between two main methods of pole extraction is presented. The matrix pencil (MP) method and the Cauchys method are used to extract poles from the radiated fields of a dipole antenna and two bowtie antennas. Results are presented for simulated fields, and the robustness to a white Gaussian noise is also analyzed. We show that the MP method allows working with lower SNR than Cauchys method and is more accurate for field reconstruction.

Resonance Behavior of Radar Targets With Aperture: Example of an Open Rectangular Cavity

In the resonance region, the radar scattering response of any object can be modelled by natural poles with the formalism of the singularity expansion method. These natural poles are resonance parameters which provide useful information for the discrimination of radar targets as their general shape, characteristic dimensions and constitution. In the case of an open radar target, high-Q internal resonances and low-Q external resonances occur respectively inside the target and on its surface. Because internal resonances have a higher Q, they may have a higher total energy and can thus be used for target identification. In this paper, we choose to study the resonance behavior of a perfectly conducting rectangular cavity with a rectangular aperture. With this simple example, we intend to show how to distinguish between the two origins of these resonances: external resonances corresponding to traveling waves on the surface of the target and internal resonances corresponding to cavity waves. Indeed, this can be applied to characterize aircrafts, whose apertures (such as inlets, open ducts, air-intakes, cavities etc.) contribute significantly to the overall radar cross section.

Characterization of radar targets in resonance domain with a reduced number of natural poles

In resonance domain, the radar scattering response can be modeled by natural poles of resonance, with the formalism of the singularity expansion method. The mapping of poles gives useful information for the discrimination of radar targets. In this paper, we show that a reduced number of poles is sufficient to characterize an object. Furthermore, we propose a procedure for selecting poles actually contributing to the scattering response. Results are presented for different canonical targets

A New Algorithm of 3D Image Reconstruction of Radar Targets from Ramp Responses in Low Frequency

Low frequency imaging in radar domain can have applications for stealthy or buried targets. The transient scattering response from a ramp waveform is related to the proflle function of the target, namely its transverse cross-sectional area along the line-of- sight, and thus provides information about the target size, orientation and geometrical shape. Such ramp responses can be used to generate a 3-dimensional image of the global shape of the target. Former imaging algorithm uses approximate limiting surfaces and is therefore limited to single convex objects. Here is proposed a new algorithm able to reconstruct non-convex as well as separated targets, from their ramp response signatures.

RCS OF LARGE BENT WAVEGUIDE DUCTS FROM A MODAL ANALYSIS COMBINED WITH THE KIRCHHOFF APPROXIMATION

In this paper, we present a fast method to predict the monostatic Radar Cross Section (RCS) in high-frequency of a cavity, which can be modeled as a succession of bent waveguides of the same cross section and stuffed by a perfectly-conducting termination. Based on a modal analysis combined with the Kirchhoff Approximation, this method allows us to obtain closed-form expressions of the transmission matrix at each discontinuity. In addition, to improve the efficiency, a selective modal scheme is proposed, which selects only the propagating modes contributing to the scattering. Compared to the Iterated Physical Optics (IPO) method and the Multi-Level Fast Multipole Method (MLFMM, generated from the commercial software FEKO), this approach brings good results for cavities with small tilt angles of the bends, typically smaller than 2 degrees.

Resonances of complex shape scattering objects: Modelling by resonant circuits

In resonance domain, the radar scattering response of any object can be modelled by natural poles of resonance with the formalism of the Singularity Expansion Method (SEM). The mapping of poles gives useful information for the discrimination of radar targets. In this paper, we propose to use resonant circuits modelling to characterize the resonance behavior of complex shape targets from the quality factor Q and the natural pulsation of resonance ¿0. For perfectly conducting (PC) canonical and complex shape targets, we present results exhibiting advantages of these two parameters {¿0 ; Q}.

Sensitivity of the singularity expansion method applied on dipole antenna backscattering

This paper deals with the sensitivity of the singularity expansion method to identify antennas. A dipole antenna is considered and the matrix pencil method is applied on its backscattered field. Then, small variations of length, diameter and load impedance are applied on the dipole antenna and the variation of poles in the complex plane is analyzed. It shows that pole extraction is very sensitive to the dimensions and load impedance of the narrow band dipole antenna.

Algorithm for profile function calculation of 3D objects: Application for radar target identification in low frequency

Ramp response technique in low frequency can be used for generating 3-dimensional images of radar targets (even stealthy or buried targets) so as to identify them. This technique uses the target proflle function, which is deflned as its transverse cross- sectional area versus distance along the observing direction. For mutually orthogonal observing views, reconstructed 3D images are quite accurate. However, in practice, due to the bias introduced from the response in shadow region and from limited non-orthogonal observing directions, reconstructions become distorted. To evaluate the quality of the reconstruction and to further identify objects from their reconstruction, we need to calculate proflle functions of 3D reconstructed objects in arbitrary directions. Therefore, in this paper, we propose an algorithm meeting this needs.