Tham khảo tài liệu 'electromagnetic waves propagation in complex matter part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 8 High Frequency Techniques the Physical Optics Approximation and the Modified Equivalent Current Approximation MECA Javier Gutierrez-Meana José Á. Martinez-Lorenzo and Fernando Las-Heras University of Oviedo Spain 1. Introduction In most of the electromagnetic problems the number of unknowns to evaluate the scattered fields grows whenever the size of the antenna device or scenario increases or the working frequency becomes higher. In this context the rigorous full-wave methods . Method of Moments MoM Fast Multipole Method FMM Engheta et al. 1992 Finite-Difference Time-Domain FDTD Taflove Umashankar 1987 or Finite-Difference FrequencyDomain FDFD Rappaport McCartin 1991 Finite Element Method FEM Kempel et al. 1998 - can not tackle the analysis of such problems beyond an upper limit determined by the computational requirements in terms of time and memory. High frequency techniques consist in the asymptotic evaluation of the Maxwell s equations. As a consequence they provide good accuracy when dealing with electrically large geometries meanwhile the computational needs diminish with respect to the aforementioned methods. Within the high frequency techniques the Geometrical Optics GO and the Physical Optics PO approximation are the most extended methods due to the successful results obtained in various fields such as Radar Cross Section RCS design of reflector antennas or radioelectric coverage calculation. Since the Physical Optics approximation is detailed in the following section the Geometrical Optics is briefly summarised. The main interest in the GO lies in the fact that incident reflected and transmitted electromagnetic waves are studied based on the conservation of the energy flux along a ray tube between a source and an observation point. Therefore the Geometrical Optics is usually referred to as Ray Optics. The GO comprises two different methodologies Rossi Gabillet 2002 Ray Tracing Glassner 1989 - the starting point is the receiver or observation point .
