Abstract
This paper 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 conic, and the main reflector is shaped to achieve a prescribed far-field radiation pattern. The procedure is based on geometrical optics (GO) principles. Two distinct far-field ray structures are explored and their limitations are identified. The GO shaping results are validated by analysis provided by the accurate method of moments technique.
Highlights
Local multipoint distribution systems (LMDSs) represent a radio-based access technology with cellular architecture offering flexible telecommunication systems with possibility of application for digital interactive TV that will stimulate growth of e-commerce, telemedicine, and so forth
For operation at millimeter waves, axis-symmetric omnidirectional dual-reflector antennas may lead to compact designs and yield the wide frequency bandwidth required to operate as an LMDS base station
From geometrical optics (GO) principles, the main reflector generatrix is shaped so that rays coming from P are reflected toward the far-field region to attend a specified circularly symmetric radiation pattern GA(θ), where θ is the angle between the ray reflected by the main reflector and the z-axis
Summary
Local multipoint distribution systems (LMDSs) represent a radio-based access technology with cellular architecture offering flexible telecommunication systems with possibility of application for digital interactive TV that will stimulate growth of e-commerce, telemedicine, and so forth. Based on GO, a simple shaping procedure for dualreflector omnidirectional antennas is presented in [5]. The generating curve of the axis-symmetric subreflector is an ellipse (omnidirectional axis-displaced ellipse—OADE type) and the shaped axis-symmetric main reflector defines the antenna radiation pattern in the elevation plane. We explore dual-reflector antennas of the OADC (omnidirectional axis-displaced Cassegrain) type, where the subreflector has a virtual annular caustic and the main-reflector generatrix is shaped to control the far-field radiation in the vertical (elevation) plane. All case studies are validated by method-of-moments (MoMs) simulations, which account for all electromagnetic effects present on the reflector and horn structure [5]
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