J.R. Bergmann

Axis-Displaced Dual-Reflector Antennas for Omnidirectional Coverage With Arbitrary Main-Beam Direction in the Elevation Plane

The synthesis of classical dual-reflector antennas suited to provide omnidirectional coverages with arbitrary main-beam direction in the elevation plane is discussed. Both sub- and main reflectors are bodies of revolution generated by axis-displaced conic sections, so to transform a spherical radiation emanating from the antenna principal focus (at the symmetry axis) into an equiphase field distribution over a conical aperture. Closed-form design equations are presented for the geometric-optics synthesis of all possible configurations. Several case studies are investigated and analyzed by the accurate method of moments technique in order to validate the proposed design procedure

Classical axis-displaced dual-reflector antennas for omnidirectional coverage

The aim of this work is to discuss the synthesis and performance of classical dual-reflector antennas suited for an omnidirectional coverage. The reflector arrangements are axially symmetric with surfaces of revolution generated by axis-displaced conic sections, established from geometrical-optics (GO) standpoints to achieve omnidirectional radiation characteristics. Closed-form equations are derived for the design of all possible reflector configurations. The vector GO aperture field is also obtained, yielding an approximate analysis by the aperture method. Some pertinent geometrical characteristics and efficiency curves are then presented and discussed for several antenna configurations fed by transverse electromagnetic coaxial horns (for vertical polarization). A practical antenna design is conducted and analyzed by the method-of-moments technique, demonstrating the accuracy of the efficiency analysis yield by the aperture method for moderately large antenna apertures.

Shaping Axis-Symmetric Dual-Reflector Antennas by Combining Conic Sections

A simple procedure for the shaping of axis-symmetric dual-reflector antennas is described. The shaping procedure is based on the consecutive concatenation of local conic sections suited to provide, under geometrical optics (GO) principles, an aperture field with uniform phase, together with a prescribed amplitude distribution. The procedure has fast numerical convergence and is valid for any circularly symmetric dual-reflector configuration. To illustrate the procedure two representative configurations are investigated. The GO shaping results are validated using accurate method-of-moments analysis.

GO Shaping of Omnidirectional Dual-Reflector Antennas for a Prescribed Equi-Phase Aperture Field Distribution

A formulation is presented for shaping dual-reflector antennas designed to offer an omnidirectional coverage. The shaping procedure is based on geometrical optics (GO) principles and assumes a uniform phase distribution for the aperture field. Two distinct dual-reflector arrangements, based on the axis-displaced Cassegrain (ADC) and ellipse (ADE) configurations, are investigated. The GO shaping results are validated using the accurate analysis provided by the method-of-moments technique

Synthesis and rigorous analysis of omnidirectional dual-reflector antennas with shaped main reflector described by local conic sections

This work presents a formulation for shaping the main reflector of an axis-symmetric dual reflector antenna designed to offer an omnidirectional coverage with an arbitrary radiation pattern in the vertical plane. The subreflector is generated by an axis-displaced confocal conic and the main reflector is shaped to achieve a prescribed far-field radiation pattern. The shaping procedure is based on geometrical optics (GO) principles. For validation of the antenna designs, the wotk employs technique by the accurate method of moments technique.

A shaped reflector antenna for mobile communications

The characteristics of a shaped reflector antenna with omnidirectional radiation pattern are presented with a view towards its possible application in radio base stations for cellular communications at microwave frequencies and above. It comprises a single circularly symmetrical shaped reflector surface fed by an axial horn and synthesized for a cosecant squared secondary antenna pattern in the vertical plane while complying with omnidirectional specifications in the azimuthal plane. Numerical results for a physical optics (PO) reflector surface synthesis considering a rigorous feed model highlight the main features of the proposed design.

A Robust Mode-Matching Algorithm for the Analysis of Triaxial Well-Logging Tools in Anisotropic Geophysical Formations

In this paper, a new pseudoanalytical axial mode-matching formulation is introduced to provide a flexible technique for analyzing direction well-logging tools in anisotropic formations. The presented technique does not rely on spatial discretization as former well-known methods. In this problem, a number of coil antennas with arbitrary relative tilt angle with respect to the symmetry axis are used to radiate electromagnetic fields in a cylindrically layered medium with both axial and radial stratifications, composed of a metallic mandrel, a borehole, and a surrounding layered earth formation. This configuration corresponds to that of triaxial well-logging tools used for oil and gas exploration. Our approach combines closed-form solutions of Maxwell’s equations for uniaxially anisotropic media in cylindrical coordinates with the generalized scattering matrix (GSM) at each axial discontinuity based on the mode-matching technique. The electromagnetic field from the tilted-coil source is represented by a set of modal coefficients that, after computation using GSM matrices, are used to extract the transimpedances of the well-logging tool.

Analysis of Omnidirectional Dual-Reflector Antenna and Feeding Horn Using Method of Moments

A hybrid numerical technique is applied for the analysis of circularly symmetric dual reflector antenna fed by TEM coaxial horn to generate an omnidirectional radiation pattern. By following the steps of a technique developed for the analysis of horn antennas, it employs a stepped-waveguide method to analyze the interior surfaces of the TEM coaxial horn transition and the electric field integral equation (EFIE) is applied on the outer surfaces of the TEM coaxial horn including the radiating aperture and the reflectors. Simultaneously, the magnetic field integral equation (MFIE) is employed on the aperture to relate the aperture fields and those in the horn transition. Method of moments (MoM) is employed to numerically solve the resultant hybrid field integral equation. The technique is applied for electromagnetic analysis of a coaxial TEM horn antenna and an omnidirectional dual reflector antenna. Results for the antenna return loss at the input port and for the vertical radiation pattern are given and compared with measurements and with commercial software results.

Improvements on the Search Modal Propagation Constants in Lossy Circular Waveguides

In this letter, we review the calculation of the propagation constants in a circular lossy waveguide. We highlighted some improvements in order to find the propagation constants of the guided modes. We present a new characteristic equation that simplifies the application of the winding number technique described in previous publications, and also we discussed some numerical criteria for the application of this technique.

Main-Reflector Shaping of Omnidirectional Dual Reflectors Using Local Conic Sections

This work presents an alternative method for GO synthesis of dual-reflector antennas suited for omnidirectional coverage. Both reflectors are bodies-of-revolution where a single conic section generates the sub-reflector while a concatenation of local conic sections represent the main-reflector generatrix, which is shaped to provide an arbitrary radiation pattern in the antennas elevation plane. To illustrate the method, omnidirectional axis-displaced ellipse (OADE) configurations are synthesized to provide a cosecant squared radiation pattern in the elevation plane. Two different ray structures are considered: with real or virtual main-reflector caustics. The GO shaping results are validated by method-of- moments simulations.