The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Y Rahmatsamii - One of the best experts on this subject based on the ideXlab platform.
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novel metal only low profile high gain stepped Reflector Antennas for future 5g mmwave and cubesat applications
International Symposium on Antennas and Propagation, 2018Co-Authors: Vignesh Manohar, Joshua M Kovitz, Y RahmatsamiiAbstract:Several emerging technologies such as next generation CubeSats and 5G mm Wave networks require Antennas capable of providing high data rates while maintaining a small form factor. This paper describes a systematic approach for synthesizing high gain stepped Reflector Antennas with profile heights of the order of a wavelength, resulting in a very small form factor for mmWave bands. The Reflector aperture is comprised of confocal parabolic sections which scatter in phase, resulting in a focused far field beam. Both symmetric and offset configurations are discussed. In particular, two distinct methods of synthesizing low profile offset Reflectors are presented in this work, which makes it possible to meet application specific design constraints.
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a spline profiled conical horn antenna assembly optimized for deployable ka band offset Reflector Antennas in cubesats
International Symposium on Antennas and Propagation, 2016Co-Authors: Joshua M Kovitz, Vignesh Manohar, Y RahmatsamiiAbstract:With the advent of small-scale satellite technologies, there has been significant interest in developing advanced functionalities for CubeSat and SmallSat projects. Developing high-gain Antennas within this paradigm opens the door for many new applications which require high data rates or narrow-beam patterns. In this paper, we discuss the optimization of a compact, spline-profile horn antenna assembly that could be used as a feed for future deployable offset Reflector Antennas in CubeSats.
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Reflector Antennas an antenna topology that never gets old
International Symposium on Antennas and Propagation, 2016Co-Authors: Y RahmatsamiiAbstract:Reflector Antennas are perhaps the most recognized type of Antennas with vast applications in satellite communications, radars, wireless communications, remote sensing, planetary missions, radio astronomy and others. Typical frequency ranges of operations have been as low as the P-band, microwave, millimeter wave, and as high as THz and optical. Reflector antenna designs have evolved from simple single Reflector topology with a solid surface to sophisticated mesh Reflector Antennas with multiple non-conical surfaces. The basic role of a Reflector antenna is to confine most of the electromagnetic energy captured over their apertures into a focal plane or redirect the radiated field of the feed into the far field. This invited paper focuses on a concise history of Reflector antenna evolution over an extended historical time span and links it to the modern and challenging recent developments and applications. The author has particularly confined the material to the areas that have influenced his research activities.
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characterization of ka band mesh surfaces for cubesat Reflector Antennas from simple wire grid model to complex knits
United States National Committee of URSI National Radio Science Meeting, 2016Co-Authors: Vignesh Manohar, Y RahmatsamiiAbstract:This work analyzes mesh surfaces at Ka-band for its potential use in CubeSat Reflector Antennas. The simple wire grid model is used as the starting point, since it has already been analyzed in closed form by Astrakhan. However, this analytical solution, by itself, cannot accurately characterize complex mesh surfaces or the nature of joint between the wires. Thus, full wave simulations must be used to study mesh surfaces in depth. A full wave simulation of the wire grid model is first carried out and the results are validated with the Astrakhan formulation. The excellent agreement between the two encouraged us to characterize and parametrically evaluate realistic mesh structures with complex knit patterns.
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revisiting levin li acceleration method for rapid diffraction analysis of Reflector Antennas
International Symposium on Antennas and Propagation, 2015Co-Authors: A Densmore, Y RahmatsamiiAbstract:The Levin method, improved by Li, is shown to accelerate, by about three orders of magnitude, the brute-force physical optics radiation from a parabolic Reflector of 240 wavelengths, especially in the far-out sidelobe regions. Key steps involve the use of an accelerating approximation involving a delaminating quadrature suggested by Li, sampling at Chebyshev-Lobatto nodes, the Chebyshev differential matrix, and truncated singular value decomposition. This paper revisits the application of the Levin+Li method and tailors it specifically to accelerate calculations for parabolic Reflector Antennas.
Fernando J. S. Moreira - One of the best experts on this subject based on the ideXlab platform.
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GO Shaping of Omnidirectional Dual-Reflector Antennas with Arbitrary Main-Beam Direction in Elevation Plane by Connecting Conic Sections
International Journal of Antennas and Propagation, 2018Co-Authors: Rafael A. Penchel, Jose R. Bergmann, Sandro R. Zang, Fernando J. S. MoreiraAbstract:This work discusses an alternative geometrical optics (GO) technique to synthesize omnidirectional dual-Reflector Antennas with uniform aperture phase distribution together with an arbitrary main-beam direction for the antenna radiation pattern. Sub- and main Reflectors are bodies of revolution generated by shaped curves defined by local conic sections consecutively concatenated. The shaping formulation is derived for configurations like ADC (axis-displaced Cassegrain) and ADE (axis-displaced ellipse) omnidirectional Antennas. As case studies, two configurations fed by a TEM coaxial horn are designed and analyzed by a hybrid technique based on mode matching and method of moments in order to validate the GO shaping procedure.
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shaping axis symmetric dual Reflector Antennas by combining conic sections
IEEE Transactions on Antennas and Propagation, 2011Co-Authors: Fernando J. S. Moreira, J R BergmannAbstract: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.
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high frequency asymptotic formulation for prompt response of parabolic Reflector Antennas
Aeu-international Journal of Electronics and Communications, 2010Co-Authors: Cassio G Rego, Sandro T M Goncalves, Fernando J. S. MoreiraAbstract:This work presents some important concepts for the temporal characterization of Reflector Antennas based on the determination of the transient antenna response together with a useful definition of the early-time antenna radiation pattern. The concepts are useful in the analysis and design of Reflector Antennas intended for high resolution radars and for high capacity digital, and UWB communication systems. 2008 Elsevier GmbH. All rights reserved.
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classical axis displaced dual Reflector Antennas for omnidirectional coverage
IEEE Transactions on Antennas and Propagation, 2005Co-Authors: Fernando J. S. Moreira, J R BergmannAbstract: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.
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generalized classical axially symmetric dual Reflector Antennas
IEEE Transactions on Antennas and Propagation, 2001Co-Authors: Fernando J. S. Moreira, A PrataAbstract:This work presents a generalized study of classical axially symmetric dual-Reflector Antennas. The antenna dishes are simply described by conic sections, arranged to reduce the main-Reflector radiation toward the subReflector surface. The dual-Reflector configuration provides a uniform-phase field distribution over the illuminated portion of the aperture, starting from a spherical-wave feed source at the antenna primary focus. All possible configurations are characterized into a total of four distinct groups. Simple closed-form design equations and the aperture field distribution are derived, in a unified way, for all these kinds of generalized Antennas using the principles of geometrical optics. The formulation is applied in a parametric study to establish the configurations yielding maximum radiation efficiency (not including diffraction effects). The design procedure is exemplified in the synthesis of a novel configuration, which is further analyzed by the moment method.
Lotfollah Shafai - One of the best experts on this subject based on the ideXlab platform.
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compact dual circularly polarized primary feeds for symmetric parabolic Reflector Antennas
IEEE Antennas and Wireless Propagation Letters, 2016Co-Authors: Ali M Mehrabani, Lotfollah ShafaiAbstract:Four-arm Archimedean spiral Antennas, capable of generating both senses of circular polarization with broadside radiation patterns, are investigated as a primary feed in symmetrical parabolic Reflector Antennas with circular rims. Unidirectional, center-fed, and compact spiral Antennas are studied, backed by a planar Reflector as a ground plane. Both right- and left-handed circularly polarized fields with broadside radiation patterns, according to the first and third modes of the spiral, are realized by confining the radiation zone to less than a three-wavelength circumference. The proposed feed exhibits excellent pattern symmetry and axial ratios well below 0.5 dB at the boresight direction for both senses of polarization. In this letter, the performance of the proposed spiral antenna is fully addressed as primary feeds in symmetrical parabolic Reflector Antennas. Different antenna parameters such as gain, cross polarization, and efficiency are studied for paraboloids, having different focal-length-to-diameter ratios, for both senses of circular polarization. Efficiencies of 70% and higher are obtained over a frequency band of 2.5-5.0 GHz.
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Analytical Models of Dual-Polarized Primary Matched Feeds for Offset Reflector Antennas With Low Cross-Polarization Properties at Both Asymmetry and Diagonal Planes
IEEE Transactions on Antennas and Propagation, 2016Co-Authors: Z. A. Pour, Lotfollah ShafaiAbstract:Conjugate-matched primary feeds for offset Reflector Antennas are reviewed and investigated for both x- and y-polarized cases. Tapered dual-mode circular waveguide feeds are analytically modeled to support a ${\rm {TE}}_{11}$ -type mode with unequal beamwidths and the ${\rm {TE}}_{21}$ -type mode for the two orthogonal polarizations. First, required mode content factors and tapering numbers of the ${\rm {TE}}_{11}$ mode are addressed for the y-polarized case in offset Reflectors with different focal length-to-diameter ratios. Then, the model is appropriately tailored for the x-polarized primary feeds. It is shown that when the polarization orientation changes, the corresponding beamwidths of the ${\rm {TE}}_{11}$ mode should be swapped in the principal E- and H-planes. This is particularly important to simultaneously realize low cross-polarization levels at both asymmetry and diagonal planes, when a dual-polarized matched feed is utilized in offset Reflector Antennas.
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handbook of Reflector Antennas and feed systems volume i theory and design of Reflectors
2013Co-Authors: Sudhakar Rao, Lotfollah Shafai, Satish K SharmaAbstract:This is the first truly comprehensive and most up-to-date handbook available on modern Reflector Antennas and feed sources for diversified space and ground applications. There has never been such an all-encompassing Reflector handbook in print, and no currently available title offers coverage of such recent research developments. The Handbook consists of three volumes. Volume I provides a unique combination of theoretical underpinnings with design considerations and techniques. The need for knowledge in Reflector Antennas has grown steadily over the last two decades due to increased use in space and ground applications, as well as their high gain and wide bandwidth capabilities at relatively low cost. This volume brings you to the leading edge of developments in the field related to numerical techniques, classical Reflector geometries, adaptive Reflector Antennas, shaped Reflectors, bifocal and bicollimated dual Reflectors, advanced Reflectors, and reflect arrays. A must-have reference for both practicing engineers as well as academic researchers.
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a simplified feed model for investigating the cross polarization reduction in circular and elliptical rim offset Reflector Antennas
IEEE Transactions on Antennas and Propagation, 2012Co-Authors: Z. A. Pour, Lotfollah ShafaiAbstract:An analytic model for the primary feed of offset Reflector Antennas is presented that facilitates a more general investigation of the cross polarization reduction in both asymmetric and inter-cardinal planes. It includes both first and second order azimuthal modes, primarily the TE11 and TE21 type modes, and allows selection of symmetric and asymmetrical patterns, with different field tapers in the principal planes. Using this model first the influence of the second order TE21 mode on the cross polarization of an offset Reflector with a circular rim is investigated. Then, the problem for an offset Reflector with an elliptic rim is also studied. It is shown that minimizing the cross polarization in the asymmetric plane does not necessarily reduce it globally, as in the inter-cardinal plane it remains high. The procedure for reduction of the cross polarization globally and its effects on the sidelobe levels of the Reflector antenna are also investigated. With the proposed feed model, the aperture efficiency of the Reflector antenna is improved compared with a standard Gaussian feed with the same edge taper. Based on this study, a dual-mode circular waveguide horn is also proposed and designed. Its performance on an offset Reflector antenna is studied and shown that the cross polarization levels are reduced quite satisfactorily within a respectable frequency band.
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multiple phase center performance of Reflector Antennas using a dual mode horn
IEEE Transactions on Antennas and Propagation, 2006Co-Authors: Lotfollah Shafai, Satish K Sharma, Bhashyam Balaji, Anthony Damini, G HaslamAbstract:A new application for Reflector Antennas is proposed and developed. Using the aperture theory, a phase center on the Reflector aperture is determined and shown that, its location is dependent on the field distribution. The proposed concept is, initially, verified by using a symmetric Reflector. It is shown that the phase center is located at the aperture geometric center, when the Reflector is illuminated symmetrically about its principal planes. Then, a dual mode feed, employing TE11 and TM01 modes, is used for generating different Reflector illuminations, and causing displacement of its phase center. The concept is then extended to offset Reflectors, and the influence of the Reflector geometry on the phase center displacement and other Reflector electrical parameters is investigated. Based on the established feed radiation pattern requirements, a feed horn is designed using circular waveguide that can propagate both modes. By modifying the amplitude and phase of the modes in the horn, a controlled asymmetric Reflector aperture field is achieved. A prototype feed horn is fabricated and tested for its dual mode radiation patterns. The results are in good agreement with simulations. The Reflector phase center properties are then investigated, by using the designed feed. A Reflector-feed assembly, with its dual phase center capability, was developed for improving the performance of the ground moving target indicator radars. The concept allows the conversion of a single Reflector to two or more Reflectors, simply by modifying the mode excitation amplitudes and phases, in the feed alone
J R Bergmann - One of the best experts on this subject based on the ideXlab platform.
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shaping axis symmetric dual Reflector Antennas by combining conic sections
IEEE Transactions on Antennas and Propagation, 2011Co-Authors: Fernando J. S. Moreira, J R BergmannAbstract: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.
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go shaping of omnidirectional dual Reflector Antennas for a prescribed equi phase aperture field distribution
IEEE Transactions on Antennas and Propagation, 2007Co-Authors: F.j. Da Silva Moreira, A Prata, J R BergmannAbstract: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
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classical axis displaced dual Reflector Antennas for omnidirectional coverage
IEEE Transactions on Antennas and Propagation, 2005Co-Authors: Fernando J. S. Moreira, J R BergmannAbstract: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.
A Prata - One of the best experts on this subject based on the ideXlab platform.
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go shaping of omnidirectional dual Reflector Antennas for a prescribed equi phase aperture field distribution
IEEE Transactions on Antennas and Propagation, 2007Co-Authors: F.j. Da Silva Moreira, A Prata, J R BergmannAbstract: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
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generalized classical axially symmetric dual Reflector Antennas
IEEE Transactions on Antennas and Propagation, 2001Co-Authors: Fernando J. S. Moreira, A PrataAbstract:This work presents a generalized study of classical axially symmetric dual-Reflector Antennas. The antenna dishes are simply described by conic sections, arranged to reduce the main-Reflector radiation toward the subReflector surface. The dual-Reflector configuration provides a uniform-phase field distribution over the illuminated portion of the aperture, starting from a spherical-wave feed source at the antenna primary focus. All possible configurations are characterized into a total of four distinct groups. Simple closed-form design equations and the aperture field distribution are derived, in a unified way, for all these kinds of generalized Antennas using the principles of geometrical optics. The formulation is applied in a parametric study to establish the configurations yielding maximum radiation efficiency (not including diffraction effects). The design procedure is exemplified in the synthesis of a novel configuration, which is further analyzed by the moment method.
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generalized classical axially symmetric dual Reflector Antennas
IEEE Antennas and Propagation Society International Symposium, 1997Co-Authors: Fernando J. S. Moreira, A PrataAbstract:Classical axially-symmetric Cassegrain and Gregorian Reflectors are widely used in high-gain antenna applications. The main disadvantage of these configurations is the subReflector blockage, which causes a number of deleterious effects. However, this problem can be reduced by decreasing the main-Reflector radiation toward the subReflector. This may be accomplished either by shaping both Reflectors or by using alternative classical configurations. This work considers the second option by presenting, in an unified way, generalized classical axially-symmetric configurations that prevent, from a geometrical optics (GO) stand point, the main-Reflector scattered energy from striking the subReflector surface. Starting from initial design variables, closed-form expressions are derived for the relevant surface parameters, as well as for the corresponding aperture field distributions. These expressions can be used as effective design tools to determine the final antenna geometry or even to establish an initial configuration for a shaping procedure.
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a design procedure for classical offset dual Reflector Antennas with circular apertures
IEEE Transactions on Antennas and Propagation, 1994Co-Authors: K W Brown, A PrataAbstract:A geometrical optics procedure for designing electrically optimized classical offset dual Reflector Antennas with circular apertures is presented. Equations are derived that allow the size and spacing of the main and subReflectors of the antenna system, along with the feed horn subintended angle, to be used as input variables of the design procedure. The procedure, together with these equations, yields an optimized design, starting from general system requirements. The procedure is demonstrated by designing both an offset Cassegrain and an offset Gregorian antenna, and is validated by analyzing their radiation patterns using physical optics surface current integration on both the main and subReflectors. >
