Physical Optics Region Research Articles

An efficient iterative hybrid multilevel fast multipole algorithm‐ physical optics method for simulating antenna mounted on the electrically large platform

An efficient iterative hybrid multilevel fast multipole algorithm (MLFMA) and the physical optics (PO) is presented to efficiently analyze the large size antenna mounted on the electrically large platform, in which, the MLFMA is used to accelerate the impedance matrix–vector multiply procedure of method of moment (MoM) and the PO is employed to simulate the large platform. In this hybrid scheme, to overcome the computational cost required in the evaluation of the electrically large PO region contribution to the MLFMA region, the strategy of the efficient iterative MoM-PO (EI-MoM-PO) is employed. In addition, the electrically large PO region shadowing effect coefficient will be checked before the computation of PO current, then the coefficient will be stored in bit format by using the Bitmap index method which is general enough to reduce the CPU time and memory consumption. The combination of EI-MLFMA-PO and Bitmap assists us to construct a proposed method that can reduce the computation cost dramatically and obtain good accuracy. Several examples are demonstrated to validate and prove the accuracy and efficiency of our method compared with the hybrid MLFMA-PO method in FEKO.

Iterative FEBI-PO Hybrid Method for Analyzing Scattering Problems of Complex Structures Having Junctions With Large-Scale Platform

An iterative hybrid of finite element boundary integral (FEBI) method and physical optics (PO) is presented for scattering problems of complex structures having junctions with electrically large-scale platform. The treatment of basis functions on the junctions between complex structures and platform is discussed in detail. Moreover, the multilevel fast multipole algorithm and the adaptive cross approximation method are employed to accelerate the solution of FEBI and the computation of interaction between FEBI and PO regions, respectively. Compared with FEBI method, the hybrid method can efficiently reduce the number of unknowns and the computational complexity while preserving acceptable accuracy. In addition, the alternative implementation of FEBI and PO can also maintain good independence of the two methods. Some numerical results are discussed to demonstrate the efficiency and accuracy of the approach.

A Chebyshev Approximation Technique Based on AIM-PO for Wideband Analysis

A novel hybrid method combining the adaptive integral method (AIM) and physical optics (PO) with Chebyshev approximation technique (CAT) is presented for wideband analysis of antennas in the presence of electrically large conducting platforms. In the hybrid AIM-PO method, the AIM is applied to reduce the memory requirement of the method of moments (MoM) impedance matrix and the MoM-PO interaction matrix. Significant speed enhancement is achieved by acceleration of the matrix-vector multiplications with fast Fourier transform (FFT) in MoM and PO regions. To achieve fast frequency sweeping, the CAT technique is employed to expand the unknown current coefficients into a Chebyshev series. Instead of direct point-by-point simulations, it is only necessary to calculate the currents by AIM-PO at several Chebyshev-Gauss frequency sample points. Two examples show that the hybrid technique can greatly reduce the computation time without loss of accuracy.

Numerical Simulation of Scattering by a Wedge With Periodic Anisotropic Impedance Faces

Plane wave scattering by an infinite, three-dimensional wedge whose faces are characterized by periodic anisotropic impedances is investigated. An improved hybrid of the moment method (MM) and the physical optics (PO) is proposed to calculate the equivalent electric current on the wedge surface. As for the infinite periodic wedge surface, a periodic representation of the scattering surface is used to prevent nonphysical edge effects in the scattering evaluation. The surface of the wedge is split into an MM region and a PO region. In the implementation of MM, the evaluation of the interaction matrix elements in the MM region is simplified by deriving six universal series. Moreover, the PO-current is modified by a diffracted current to improve its accuracy. The accuracy and effectiveness of the proposed approach is validated and demonstrated by using series solution, the method in [T. B. A. Senior, “Solution of a class of impedance wedge problem for skew incident,” Radio Sci., vol. 21, no. 2, pp. 185-191, 1986], and the two-dimensional improved MM-PO approach under several canonical two-dimensional wedge cases. At last, the proposed approach is applied to analyze the scattering from the wedges with periodic anisotropic impedance faces, and the numerical results are presented.

Analyzing Electromagnetic Systems on Electrically Large Platform Using a GTM-PO Hybrid Method with Synthetic Basis Functions

A hybrid method of generalized transition matrix (GTM) and physical optics (PO) with synthetic basis functions (SBF) is proposed to analyze electromagnetic systems on electrically large platforms. Based on domain decomposition method (DDM), the proposed approach is to divide the whole problem into a GTM region and a PO region. The GTM algorithm can simulate antennas and scatterers accurately, and the PO algorithm is applied to obtain current distribution on the electrically large platform. With the characteristics extraction technique using SBFs on the GTM models, the number of unknowns can be greatly reduced and the computational efficiency can be further improved. PO region is regarded as an environment background and the unknowns in the PO region need not to be directly solved. Numerical examples will be shown to demonstrate the feasibility of the hybrid method.

MLFMA-PO Hybrid Technique for Efficient Analysis of Electrically Large Structures

A hybrid technique combining the multilevel fast multipole algorithm (MLFMA) and the physical optics (PO) is presented for analyzing scattering and radiation by electrically large structures. In this technique, MLFMA is used to characterize the complex parts such as antennas that cannot be analyzed by high-frequency asymptotic methods. The large smooth bodies are calculated using PO method because of its high computational efficiency. The interaction between method-of-moments (MoM) region and PO region is strictly considered and accelerated by MLFMA, which can guarantee the high efficiency without losing the calculation accuracy. Numerical results are given to demonstrate the reasonable accuracy and high capability of the proposed hybrid technique compared to the conventional MLFMA and MoM-PO method.

Radiation Analysis of Antenna Around Electrically Large Platform Using Improved MoM-PO Hybrid Method

An improved current-based analysis combining the method of moments (MoM) with physical optics (PO) approximation is presented for antenna around an electrically large platform. In the analysis, the whole surface of the platform and the antenna is divided into three regions, namely, the MoM region, the lit PO region and the shadowed PO region, respectively. The shadowed currents are modified by a simple method of non-uniform grid. Furthermore, a new set of pulse vector basis functions is used to represent the currents in the PO region. The primary objective of applying these basis functions is to analyze the radiation of antenna around conducting, dielectric, or composite platforms. However, in the present work, only the conducting platform solution is presented and compared with other data.

Efficient IE-FFT and PO Hybrid Analysis of Antennas Around Electrically Large Platforms

An efficient hybrid analysis that combines integral equations (IE) with physical optics (PO) approximation is presented for antennas around an electrically large platform. In the analysis, the whole surface of the platform and antennas is divided into two regions, namely, the full-wave region and the PO region. In the full-wave region, the IE is modified by coupling into the PO contribution. Similar to the fast IE method, the modified impedance matrix is decomposed into the near-field couplings and the well-separated group couplings, respectively. By interpolating the Green's function, the couplings between two well-separated groups can be computed using fast Fourier transform (FFT). Due to the PO approximation, the hybrid method utilizes fewer unknowns and requires less solution time than the conventional IE-FFT.

Efficient Current-Based Hybrid Analysis of Wire Antennas Mounted on a Large Realistic Aircraft

An efficient hybrid analysis which hybridizes surface-wire integral equations (SWIE) with physical optics (PO) approximation is presented for wire antennas attached to an electrically large aircraft platform. In the analysis, the whole surface of the platform and antennas is divided into three regions, namely, the method of moments (MoM) region, the PO region and a region referred to as the joint PO-MoM (POM) region in this paper. The MoM region, generally, the smallest one among the three regions, includes wires, wire-surface junctions and a small part of the platform surface surrounding the junctions. A large part of the remaining platform surface forms the PO region with the rest being the POM region which is situated between the MoM and PO regions. The POM region is treated as a MoM region on the one hand so that the total MoM region is sufficiently large to well characterize the platform-attached antennas, whereas it is also regarded as a PO region on the other hand so that its interaction with the PO region needs not to be precisely considered so as to drastically reduce computational requirements.

HYBRID METHOD OF HIGHER-ORDER MOM AND NYSTRÖM DISRETIZATION PO FOR 3D PEC PROBLEMS

This paper presents an e-cient and accurate hybrid approach of method of moments (MoM) and physical optics (PO) for radiation problems such as antennas mounted on a large platform. The new method employs higher-order hierarchical Legendre basis functions in the MoM region and higher-order Nystrom scheme in the PO region. The two regions are both discretized with large domains. The unknowns can be much less than those in the small-domain MoM- PO solutions, which will lead to a great reduction in computation complexity. Furthermore, with the Nystrom scheme in the PO region, the higher-order accuracy is maintained, and the calculation of the impedances can be more e-cient than that in the existing higher- order MoM-PO procedure. Numerical results show the validity of the proposed method.

An Efficient Hybrid Method for Analysis of Slot Arrays Enclosed by a Large Radome

A hybrid method that combines the integral equation (IE) method and Physical Optics (PO) is proposed for efficient analysis of slot arrays enclosed in an electrically large radome. The integral equations are applied over the aperture of the slot antenna and the tip region of the radome by enforcing continuity of the tangential magnetic or electric field. Equivalent PO currents are assumed on the relatively smooth region of the radome walls, induced by the radiated fields from the antenna. The radiated fields due to the PO currents on the radome are coupled back to the integral equations to account for interactions between the radome and the antenna, as well as the interactions between the tip and other parts of the radome. This method leads to considerable reduction in memory and computational time, since PO is applied to a large part of the electrically large radome, with unknown currents defined only on the aperture of the slot antenna and the small tip region of the radome. Better efficiency can be attained if the integral equation is applied only to the slot aperture and the entire radome wall taken as the PO region, with acceptable degradation in accuracy.

Higher order hybrid method of moments-physical optics modeling technique for radiation and scattering from large perfectly conducting surfaces

An efficient and accurate higher order, large-domain hybrid computational technique based on the method of moments (MoM) and physical optics (PO) is proposed for analysis of large antennas and scatterers composed of perfectly conducting surfaces of arbitrary shapes. The technique utilizes large generalized curvilinear quadrilaterals of arbitrary geometrical orders in both the MoM and PO regions. It employs higher order divergence-conforming hierarchical polynomial basis functions in the context of the Galerkin method in the MoM region and higher order divergence-conforming interpolatory Chebyshev-type polynomial basis functions in conjunction with a point-matching method in the PO region. The results obtained by the higher order MoM-PO are validated against the results of the full MoM analysis in three characteristic realistic examples. The truly higher order and large-domain nature of the technique in both MoM and PO regions enables a very substantial reduction in the number of unknowns and increase in accuracy and efficiency when compared to the low-order, small-domain MoM-PO solutions. The PO part of the proposed technique, on the other hand, allows for a dramatic reduction in the computation time and memory with respect to the pure MoM higher order technique, which greatly extends the practicality of the higher order MoM with a smooth transition between low- and high-frequency applications.

Improvement of the hybrid moment method–physical optics method through a novel evaluation of the physical optics operator

AbstractThis paper presents an alternative procedure for the evaluation of the physical optics (PO) contribution into a hybrid moment method–physical optics (MM–PO) code. The proposed formulation includes a linear interpolation of the phase over large triangular subdomains for the PO regions, where the radiated field can be analytically determined. This allows a drastic reduction of the computational cost, while maintaining or even improving the degree of accuracy. In this way, the scope of application of the MM–PO hybrid code is enhanced to larger problems in terms of wavelength. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 357–363, 2001.

Improvement of the PO-MoM hybrid method by accounting for effects of perfectly conducting wedges

A correction of the conventional physical optics (PO) current close-to-perfectly conducting wedges based on an application of the uniform geometrical theory of diffraction (UTD) is presented. This improved PO current is used in a hybrid formulation in combination with the method of moments (MoM) to deal with three-dimensional scattering bodies of arbitrary shape. The accuracy of this hybrid method is demonstrated by some examples. As opposed to an application of the physical theory of diffraction (PTD), only surface current densities and no fictitious electric and magnetic line currents along the edges are involved which allows a uniform treatment of the MoM and the PO region by expressing the surface current density as a superposition of basis functions defined over triangular patches. >

Training Experiments for Students Using Lasers

Though He-Ne lasers became popular even for high school students, scarce reportas to make them ready at hand in a high school and college education program can be seen.In this paper new physical experiments for student training using lasers are described with evaluation of accuracy and the remarkes in training practice.In geometrical optics field, an educational program of it in connection to the linear algebra is proposed and experiments for new geometrical optics are described. In physical optics region, experimental devices for the education of interference and diffraction are described.In material constant measurement field, refractive indices measurements from Brewster angle and critical angle of total reflection, both using lasers are reported.

Far field scattering from bodies of revolution

By use of approximations based on physical reasoning radar cross-section results for bodies of revolution are found. In the Rayleigh region (wavelength large with respect to object dimensions) approximate solutions are found. Examples given include a finite cone, a lens, an elliptic ogive, a spindle and a finite cylinder. In the physical optics region (wavelength very small with respect to all radii of curvature) Kirchhoff theory and also geometric optics can be used. When the body dimensions are only moderately large with respect to the wavelength, Fock or Franz theory can be applied, and examples of the circular and elliptic cylinder are presented. In the region where some dimensions of the body are large with respect to the wavelength and other dimensions are small with respect to the wavelength, special techniques are used. One example, the finite cone, is solved by appropriate use of the wedge-like fields locally at the base. Another example is the use of traveling wave theory for obtaining approximate solutions for the prolate spheroid and the ogive. Other results are obtained for cones the base perimeter of which is of the order of a wavelength by using known results for rings of the same perimeter.