Locality of high frequency electromagnetic scattering phenomena is embodied and imported to the Method of Moments (MoM) to reduce computational load. The proposed method solves currents on small areas only around inner and edge stationary phase points (SPPs) on the scatterer surfaces. The range of MoM area is explicitly specified in terms of Fresnel zone number as a function of frequency, source and observer positions. Based upon this criterion, scatterer of arbitrary size and shape can be solved with almost frequency independent number of unknowns. In some special cases like focusing systems, locality disappears and the method reduces to the standard MoM. The hybrid method called PO-MoM is complementarily introduced to cope with these cases, where Fresnel zone number with analogous but different definition is used. The selective use of Local-MoM and PO-MoM provides frequency insensitive number of unknowns for general combination of source and observation points. Numerical examples of RCS calculation for two dimensional flat and curved surfaces are presented to demonstrate the accuracy and reduction of unknowns of this method. The Fresnel zone, introduced in the scattering analysis for the first time, is a useful indicator of the locality or the boundary for MoM areas.

We have proposed a unique and simple modification to the definition of surface-normal vectors in Physical optics (PO). The modified surface-normal vectors are so defined as that the reflection law is satisfied at every point on the surface. The PO with currents defined by this new surface-normal vector has the enhanced accuracy for the edged scatterers to the level of Geometrical Theory of Diffraction (GTD), though it dispenses with the knowledge of high frequency asymptotic techniques. In this paper, firstly, the remarkable simplicity and the high accuracy of the modified PO as applied to the analysis of Radar Cross Section (RCS) is demonstrated for 2 dimensional problems. Noteworthy is that the scattering not only from edge but also from wedge is accurately predicted. This fringe advantage is confirmed asymptotically by comparing the edge and wedge diffraction coefficients of GTD. Finally, the applicability for three dimensional cube is also demonstrated by comparison with experimental data.

We have derived the novel extended UTD (Uniform Geometrical Theory of Diffraction) solution and the novel modified UTD solution for the back scattering of an incident whispering gallery (WG) mode on the edge of a cylindrically curved conducting sheet. By comparing with the reference solution obtained from the integral representation of the scattered field by integrating numerically along the integration path, we have confirmed the validity and the utility of the novel asymptotic solutions proposed in the present study. It is shown that the extended UTD solution can be connected smoothly to the modified UTD solution on the geometrical boundary separating the edge-diffracted ray and the surface-diffracted ray.

When a cylindrically curved concave conducting surface is terminated abruptly at the edge, the whispering gallery (WG) mode propagating toward the edge direction is radiated into the free space from the aperture plane at the edge. In this paper, by applying the new analysis method, we shall derive a uniform geometrical theory of diffraction solution (UTD) for the electric-type WG mode radiation field applicable in the transition region near the geometrical boundaries produced by the incident modal ray on the edge of the curved surface. The UTD is represented by the summation of the solution for the geometrical ray converted from the modal ray of the WG mode and the solution for the uniform edge diffracted ray scattered at the cylindrically curved edge. By comparing with the reference solution obtained numerically from the integral representation of the radiation field, we will confirm the validity and the utility of the UTD proposed in this paper.

This paper presents a prediction of the millimeter-wave multipath propagation characteristics in the typical urban environment. To analyze the propagation in an outdoor environment, the three dimensional model based on the geometrical optics and the uniform geometrical theory of diffraction is employed. Prediction by the three dimensional ray tracing method needs a detailed map, which records locations and shapes of obstacles surrounding a transmitter and a receiver. It is usually difficult to create a complete map because tremendous data is necessary to describe the area structure. We propose, in this report, a three dimensional propagation model to predict the millimeter wave propagation characteristics by using the information available from only a map on the market. This approach gives us much convenience in the actual design. The modeled results are demonstrated and furthermore comparison are made between the simulated results and the experimental data.

A simple extension to treat evanescent modal excitation at the aperture of a parallel plane waveguide is shown here by GTD diffracted rays with complex propagation angles. Numerical comparison with other solution confirmed that our simple solution can be used for modal excitation estimation below the cut-off frequency.

This paper presents a configuration of circularly polarized annular-ring microstrip antenna (ARMSA) and its design method to obtain high gain and low axial ratio including the analysis of finite ground plane effect using G.T.D. for personal satellite communication use. The ARMSA excited at TM21 mode through co-planar branch-line hybrid coupler for circular polarization produces a conical pattern which has high gain in low elevation angle. The relation of gain and axial ratio versus the dielectric constant of substrate are shown and the existence of the dielectric constant which satisfies two requirements, that is, high gain and low axial ratio are clarified. For car-top application, experimental results in the L-band showed satisfactory characteristics for vehicle antenna.

This paper describes a novel method to calculate the fields scattered by a polyhedron structure for an incident plane wave. In this method, the fields diffracted by an edge are calculated using the equivalent edge currents which are separated into components dependent on each of the two surfaces which form the edge. The separated equivalent edge currents are based on the Geometrical Theory of Diffraction (GTD). Using this Separated Equivalent Edge Current Method (SEECM) , fields scattered by a polyhedron structure can be calculated without special treatment of the singularity in the diffraction coefficient. This method can be also applied successfully to structures with convex surfaces by modeling them as polyhedron structures.

Recently most of the singularities of the equivalent edge currents for flat plates were eliminated by the authors using the paths of most rapid phase variation. A unique direction on the plate was determined for given incidence and observer. This paper extends this method for arbitrary angle wedges and presents the new expressions of the equivalent edge currents. The resultant expressions are valid for any incidence and observation aspects and have no false singularities. Diffraction patterns and radar cross sections of 3-D objects composed of wedges are calculated by using these currents. They show good agreements with experimental data or the results by the other methods.