Computation of Em Field Scattered by an Open-Ended Cavity and by a Cavity Under Radome Using the Iterative Physical Optics

Abstract

Abstract-It is always a challenge to predict Radar Cross Section (RCS) of a full scale military platform with a good accuracy. Most of the time antennas and cavities are the main contributors of aircrafts RCS. Several methods have been developed to compute the RCS of cavities such as analytical methods (modal methods) and asymptotic methods (geometrical optics (GO) methods and physical optics (PO) methods). This article presents the Iterative Physical Optics (IPO) method which consists in an iterative resolution of the Magnetic Field Integral Equation (MFIE) to compute the currents on the inner walls of the cavity. This method allows computing arbitrarily shaped cavity with a good accuracy even for cavity with a depth inferior to the wavelength. Comparisons of IPO results with Rays and Finite element methods show a better accuracy of IPO than Rays especially for cross polarization. But computation time represents one of the main limitations of the IPO method. We present here a new formulation of the Segmented IPO method which coupled with the generalized reciprocity theorem decreases significantly the complexity of the method and consequently the computation time. The S-IPO method has been validated by comparisons with Modal method and measurements. We have observed that the repartition of the electric currents density on the inner walls of the cavity is quite the same with IPO and S-IPO computations. Lastly we propose an evolution of the IPO method we have developed to compute the RCS of cavities under radome. This method has been validated by comparison with finite element results.

RCS of Large Bent Waveguide Ducts From a Modal Analysis Combined With the Kirchhoff Approximation

“…In addition, they are compared with the Iterated Physical Optics (IPO) method [14] and the Multi-Level Fast Multipole Method (MLFMM) generated by the commercial software FEKO [21]. The MLFMM is based on the MoM and has the advantage to solve electromagnetic problem with many unknowns comparatively to the MoM.…”

“…In Section 2, the mathematical formulation is addressed for a waveguide connected to a bent waveguide of same cross section, and in Section 3, the formulation is generalized to a succession of bent waveguides connected between them. In Section 4, our approach is compared with two methods: (i) The Iterated Physical Optics (IPO) one, summarized in [14], which is very appropriate for large cross sections comparatively to the wavelength; (ii) The MultiLevel Fast Multipole Method (MLFMM) one, generated from the commercial software FEKO [21]. In this paper, the multiple-edge diffraction of modal rays across the aperture is assumed to be negligible for a large cross section of the waveguide.…”

“…This is why for instance, hybrid boundaryintegral/modal approach was developed [5]. In high-frequency, when the cross section of the cavity is large comparatively to the incident wavelength λ 0 , asymptotic methods, like approaches based on ray tracing [6][7][8][9][10], Physical Optics [11][12][13][14] and modal analysis combined with the Kirchhoff Approximation for the boundary conditions [15][16][17] are also investigated. This paper applied this latter to an open ended cavity modeled as a succession of bent waveguides of same rectangular cross section and stuffed by a perfectly-conducting termination.…”

A Novel Simulation Approach of Aircraft Dynamic RCS

“…PO is an efficient high frequency method to calculate the scattering of the electrically large target surface. PTD is adopted to calculate the diffraction of the boundaries [10,11]. The body coordinate system OXY Z is fixed in the aircraft as shown in Figure 2.…”

More Accurate Hybrid Po-Mom Analysis for an Electrically Large Antenna-Radome Structure

“…Unfortunately, the MOM analysis costs so large amount of computer memory and CPU time that the conventional personal computer can not accomplish the task, when the electrical size of the radome is very large, though some accelerating methods could be adopted [6][7][8]. Some high frequency techniques are suitable for electrically large radomes [9,10] but not accurate for discontinuous structures on the radome surfaces. Recently, a hybrid method combining physical optics (PO) and MOM together, PO-MOM, has been introduced to deal with the intractable problem and proved to be efficient [11,12].…”