V-shaped deformation quadrotor radar cross-section analysis

With the continuous advancement of rotor dynamic electromagnetic scattering research, the radar cross-section (RCS) of turbofan engines has attracted more and more attention. In order to solve the electromagnetic scattering characteristics of a biaxial multirotor turbofan engine, a dynamic scattering method (DSM) based on dynamic simulation and grid transformation is presented, where the static RCS of the engine and its components is calculated by physical optics and physical theory of diffraction. The results show that the electromagnetic scattering of the engine is periodic when the engine is working stably, while the rotors such as fans and turbines are the main factors affecting the dynamic electromagnetic scattering and the ducts greatly increase the overall RCS level of the engine. The proposed DSM is effective and efficient for studying the dynamic electromagnetic scattering characteristic of the turbofan engine.

A bistatic radar cross section (RCS) formulation is developed wherein a first-order physical theory (physical optics and physical theory of diffraction) is used. A large class of curved surfaces is considered using a single parameterization. These curved surfaces, combined with flat plates, can be used to model a variety of realistic shapes. Both the physical optics current and the edge equivalent current are placed on these shapes to radiate the scattered field. The resulting surface integral is evaluated with a uniform asymptotic approach by which a smooth transition from a monostatic local response to a response of distributed nature is devised. A carefully designed shadowing scheme is used to suit all scattering configurations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A radio frequency (RF) simulation technique based on high frequency hybrid method is proposed for complex target. Firstly, the radar cross section (RCS) of the target is obtained by vector addition of facets scattering field and wedges scattering field that are calculated respectively by physical optics (PO) method and physical theory of diffraction (PTD). Then, scattering centers of the target are extracted based on multi scattering center theory, and the radar echo signal is simulated through radio frequency simulation system (RFSS). This technique could improve the fidelity of radar signal simulation and the confidence of RF simulation test. At last, simulation results validate the technique.

Racal-Thorn Wells has developed the high frequency radar cross section (RCS) prediction code, FACETS (frequency asymptotic code for electromagnetic target scattering). This code relies on frequency asymptotic electromagnetic techniques, principally physical optics, physical theory of diffraction and geometric optics ray tracing. FACETS is the prediction code that sits at the heart of a suite of programs that make up the FACETS Electromagnetic Analysis System (FEMAS). FEMAS has been developed for translating CAD target surface descriptions into a form suitable for input to the FACETS analysis program and facilitating analysis of the results. The first section of this paper discusses the FACETS RCS prediction code and the second section gives examples of how this tool has been used in the collaborative venture between Racal-Thorn Wells and DERA Space Department, to produce simulated synthetic aperture radar (SAR) images of ships from spaceborne radar geometries. (5 pages)

Facilitating learning adaptive V-tail of a supersonic missile for radar cross-section reduction during interval flight

The physical theory of diffraction (PTD) has been expanded for the case of slope diffraction, when an incident wave is zero but its derivative is not zero in the direction of a perfectly conducting scattering edge. High frequency asymptotics are found both for elementary edge waves and for the total edge waves scattered by arbitrary curved edges. Great attention is given to fields created by the nonuniform (diffraction) component of edge currents. These fields are usually called ptd corrections to the Physical Optics approach. These corrections are found for diffraction fields in ray regions and in diffraction regions such as the vicinities of shadow boundaries, smooth caustics, and foci.

This paper describes the Radar Cross Section (RCS) analysis and prediction for simple target shapes such as circular flat plate, triangular flat plate, ellipsoid, sphere, ellipsoid, truncated cone and cylinder. This paper also discusses the accuracy of physical optics (PO) approximation in measuring the far field monostatic radar cross section of different simple objects varying in size using the Matlab Programming to simulate the output graphs, and the results were compared to a more exact data obtained by CST Microwave Studio Simulation software which uses asymptotic solver in calculating RCS for these objects.

A new and simple method of interpreting the of the backscatter radar cross section (RCS) from ocean waves of individual wavelength is presented. Using the Kirchhoff scattering (Physical Optics) theory, the RCS from the ambient waveheight spectrum is first computed as a function of the wavenumber. Differentiating this cumulative RCS yields the distribution function of the RCS from ocean waves of different wavenumbers. The present study shows, as a general feature, that the maximum RCS contribution tends to come from the ocean waves of wavenumbers closer to the Bragg wavenumber as the radar incidence angle increases. Under low wind speeds (/spl sim/2 m/s) and at incidence angles between 200 and 45/spl deg/, the dominant RCS contribution at both C-band and L-band comes from ocean waves of wavenumbers close to the Bragg wavenumber. Under intermediate to high wind speeds (/spl sim/10-15 m/s) and at the small incidence angle of 200, the radar backscatter is dominated by long ocean waves with little contribution from the Bragg waves at both bands. At the intermediate incidence angles (/spl sim/35/spl deg/ to 45/spl deg/), the RCS distribution is centered at wavenumbers near the Bragg wavenumber at all wind speeds from 2 m/s to 15 m/s. These features are more pronounced at C-band than at L-band. The present theory is based on the Kirchhoff scattering model, and as such, its validity may also be limited to a range of small to intermediate incidence angles where the polarization effect is not very significant. The RCS distribution is evaluated for the ambient sea surface and the surface perturbed by varying currents induced by the interaction between the current and bottom topography.

Physical optics uses geometrical optics to estimate the surface current. This current is then used in a radiation integral to find the scattered field. PO often works very well for electrically large and smooth bodies. However, in spite of its great success in many applications, the use of an approximate current can lead to inherent limitations of its accuracy. The physical theory of diffraction (PTD) is an important high‐frequency technique that addresses this problem. The PTD became a widely used technique for the analysis and design of antennas, radar cross‐section analysis, and stealth design. The PTD theory is first developed in 2D. Its use is demonstrated by calculating the radiation pattern of a reflector antenna. It is then be generalized to 3D and applied to the scattering by a circular disc. The PTD formulation is closely related to both geometrical theory of diffraction (GTD) and uniform theory of diffraction (UTD).

Physical optics (PO) and the physical theory of diffraction (PTD) are used to determine the backscatter cross sections of dihedral corner reflectors in the azimuthal plane for the vertical and horizontal polarizations. The analysis incorporates single, double, and triple reflections; single diffractions; and reflection-diffractions. Two techniques for analyzing these backscatter mechanisms are contrasted. In the first method, geometrical optics (GO) is used in place of physical optics at initial reflections to maintain the planar nature of the reflected wave and subsequently reduce the complexity of the analysis. The objective is to avoid any surface integrations which cannot be performed in closed form. This technique is popular because it is inherently simple and is readily amenable to computer solutions. In the second method, physical optics is used at nearly every reflection to maximize the accuracy of the PTD solution at the expense of a rapid increase in complexity. In this technique, many of the integrations cannot be easily performed, and numerical techniques must be utilized. However, this technique can yield significant improvements in accuracy. In this paper, the induced surface current densities and the resulting cross section patterns are illustrated for these two methods. Experimental measurements confirm the accuracy of the analytical calculations for dihedral corner reflectors with right, acute, and obtuse interior angles.

The physical optics (PO) and the physical theory of diffraction (PTD) are in extensive use in the antenna design and RCS calculation. The specific feature of these approximations is the phenomenon of polarization coupling. This phenomenon has been known since 1975, but its physical nature is still not explained in the literature. In the present communication, it is shown that this phenomenon is caused by the charges at the edge of a scattering structure, which are accumulated there due to the discontinuity of the PO current component normal to the edge.

The generalization1 of a solution obtained for wedge wave diffracted from the rib of impedance wedge for the case of Perfectly Electrically Conducting (PEC) wedge with cover is considered. The development of the Physical Theory of Diffraction (PTD) method for calculation of reflection coefficients from PEC wedge with cover is presented. The calculations were carried out according to strict formulas and assuming that impedance wedge conditions of Leontovich on the border «cover -- free space» are satisfied. Angular diagrams of wedge waves for different values of cover thickness are obtained. Radar Cross Section (RCS) diagrams of PEC cylinder with cover are presented.

In this study, an efficient method of designing laminate composite radar absorbing structures (RAS) is proposed with consideration given to the structural shape so as to improve aircraft stealth performance. The calculation of the radar cross section (RCS) should be decreased to enhance the efficiency of the stochastic optimization when designing an RAS. In the proposed method, RAS are optimized to match up the input impedance of the minimal RCS, which is obtained by using physical optics and the transmission line theory. Single and double layer dielectric RAS for aircraft wings are employed as numerical examples and designed using the proposed method, RCS minimization and reflection coefficient minimization. The availability of the proposed method is assessed by comparing the similarity of the results and computation time with other design methods. According to the results, the proposed method produces the same results as the stochastic optimization, which adopts the RCS as the objective function, and can improve RAS design efficiency by reducing the number of RCS analyses.

An essential characteristic of any radar target is the measure of its ability to reflect energy to the receiving antenna. The parameter used to describe this ability is the radar cross section (RCS) of the target. Stealth techniques and technologies, which affect the efficiency of early warning radar systems currently in operation, are described in ref [1]. The problem is to find countermeasures that fully integrate new requirement capabilities into the current long-range radar net and infrastructure, keeping research & development, and maintenance costs, low. The netcentric approach recently proposed in ref [2] using VHF-based multi-band radar systems is a new concept for Recognized Air Picture production based on long-range radars, which offers a powerful solution for the surveillance of large areas at a reasonable cost. Target RCS behaviour, fluctuations due to aspect angle and frequency are of particular interest in these systems, because the antenna beam positioning of the "VHF", "L" (or "S") and "X" band radars should be synchronised in azimuth and elevation. Targets could change orientation, course and kinematical characteristics during the time required for beam positioning. Advance knowledge and accurate prediction of target RCS is therefore desirable in order to design and develop efficient (robust) discrimination algorithms for the optimisation of target detection, tracking and non-cooperative target recognition. This paper reviews the target RCS aspects in current radar systems of interest, and examines RCS behaviour for use in future multi-band radar system applications.

In two-dimensional problems, the physical theory of diffraction (PTD) is valid for both electromagnetic and acoustic waves. This chapter presents the theoretical fundamentals for acoustic and electromagnetic waves. To complete formulation of the diffraction problem and ensure the uniqueness of its solution, the wave equation and boundary conditions are supplemented by the Sommerfeld radiation condition for the scattered field. The high-frequency physical optics (PO) approach is widely used in acoustic and electromagnetic diffraction problems. Among the properties of the shadow radiation, the most significant are the shadow contour theorem and the total power of shadow radiation, which are verified for acoustic and electromagnetic waves, in the chapter. Taking into account the diffraction and nonuniform components of surface fields, PTD overcomes the PO shortcomings and provides more accurate asymptotic results for high-frequency scattered fields.