GTD analysis of the radiation patterns of conical horns

Abstract: The electromagnetic fields propagating up a cone having an arbitrary wall impedance are found using an asymptotic solution. Three special cases are then considered: the smooth-metal wall, the corrugated wall, and the metal wall with a lossy-dielectric lining. The last case, in the form of an absorber-lining is then shown to behave like a corrugated horn since it too provides a highly tapered E -plane and H -plane aperture distribution. Furthermore, it does this over a much larger bandwidth, over 3:1, with negligible gain drop.

Abstract: In this study, the impact of flnite ground plane edge difiractions on the amplitude patterns of aperture antennas is examined. The Uniform Theory of Difiraction (UTD) and the Geometrical Optics (GO) methods are utilized to calculate the amplitude patterns of a conical horn, and rectangular and circular waveguide apertures mounted on square and circular flnite ground planes. The electric fleld distribution over the antenna aperture is obtained by a modal method, and then it is employed to calculate the geometrical optics fleld using the aperture integration method. The UTD is then applied to evaluate the difiraction from the ground planes' edges. Far-zone amplitude patterns in the E and H planes are flnally obtained by the vectorial summation of the GO and UTD flelds. In this paper, to accurately predict the H-plane amplitude patterns of circular and rectangular apertures mounted on square ground planes, the E-plane edge difiractions need to be included because the E-plane edge difiractions are much more intense than those of the H-plane edge regular and slope difiractions. Validity of the analysis is established by satisfactory agreement between the predicted and measured data and those simulated by Ansoft's High Frequency Structure Simulator (HFSS). Good agreement is observed for all cases considered.

Abstract: An analytical procedure for predicting accurately the E -plane patterns of conical horns with moderate aperture widths ( ka ), based on uniform geometrical theory of diffraction (UGTD) and supported by measured data, is presented. This analysis predicts the E -plane patterns more accurately (over the main beam) than the one presented earlier.

Abstract: In this paper we present two simulation techniques for modeling periodic structures with three-dimensional elements in general. The flrst of these is based on the Method of Moments (MoM) and is suitable for thin-wire structures, which could be either PEC or plasmonic, e.g., nanowires at optical wavelengths. The second is a Finite Difierence Time Domain (FDTD)-based approach, which is well suited for handling arbitrary, inhomogeneous, three-dimensional periodic structures. Neither of the two approaches make use of the traditional Periodic Boundary Conditions (PBCs), and are free from the di-culties encountered in the application of the PBC, as for instance slowness in convergence (MoM) and instabilities (FDTD).

Abstract: A double conical horn which consists of two coaxially arranged conical horns is analyzed by means of a mode-matching procedure. It can be dimensioned, to produce nearly identical radiation characteristics at two different frequencies. Therefore the double conical horn can serve as a feed of reflector antennas in order to double the transmission capacity of the antenna system. A design procedure for this feed is given

Abstract: Foreword to the Revised Edition. Preface. Fundamental Concepts. Introduction to Waves. Some Theorems and Concepts. Plane Wave Functions. Cylindrical Wave Functions. Spherical Wave Functions. Perturbational and Variational Techniques. Microwave Networks. Appendix A: Vector Analysis. Appendix B: Complex Permittivities. Appendix C: Fourier Series and Integrals. Appendix D: Bessel Functions. Appendix E: Legendre Functions. Bibliography. Index.

Abstract: A compact dyadic diffraction coefficient for electromagnetic waves obliquely incident on a curved edse formed by perfectly conducting curved ot plane surfaces is obtained. This diffraction coefficient remains valid in the transition regions adjacent to shadow and reflection boundaries, where the diffraction coefficients of Keller's original theory fail. Our method is based on Keller's method of the canonical problem, which in this case is the perfectly conducting wedge illuminated by plane, cylindrical, conical, and spherical waves. When the proper ray-fixed coordinate system is introduced, the dyadic diffraction coefficient for the wedge is found to be the sum of only two dyads, and it is shown that this is also true for the dyadic diffraction coefficients of higher order edges. One dyad contains the acoustic soft diffraction coefficient; the other dyad contains the acoustic hard diffraction coefficient. The expressions for the acoustic wedge diffraction coefficients contain Fresenel integrals, which ensure that the total field is continuous at shadow and reflection boundaries. The diffraction coefficients have the same form for the different types of edge illumination; only the arguments of the Fresnel integrals are different. Since diffraction is a local phenomenon, and locally the curved edge structure is wedge shaped, this result is readily extended to the curved wedge. It is interesting that even though the polarizations and the wavefront curvatures of the incident, reflected, and diffracted waves are markedly different, the total field calculated from this high-frequency solution for the curved wedge is continuous at shadow and reflection boundaries.

Abstract: The fields diffracted by a body made up of finite axially symmetric cone frustums are obtained using the concepts of the geometrical theory of diffraction. The backscattered field for plane-wave incidence on such a target is obtained with particular emphasis on those regions that are usually avoided, namely, the caustic region and its immediate vicinity. The method makes use of equivalent electric and magnetic current sources which are incorporated in the geometrical theory of diffraction. This solution is such that it is readily incorporated in a general computer program, rather than requiring that a new program be written for each shape. Several results, such as the cone, the cylinder and the conically capped cylinder, are given. In addition, the method is readily applied to antenna problems. An example which is reported consists of the radiation by a stub over a circular ground plane. This present theory yields quite good agreement with experimental results reported by Lopez, whereas the original theory given by Lopez is in error by as much as 10 dB.