W. Imbriale

Bio: W. Imbriale is an academic researcher. The author has contributed to research in topics: Parabolic reflector & Cassegrain antenna. The author has an hindex of 1, co-authored 1 publications receiving 54 citations.

Large lateral feed displacements in a parabolic reflector

Abstract: The radiation patterns of a parabolic reflector with large lateral-feed displacements are computed utilizing both the vector current method and scalar aperture theory, and compared to experimental results. The theory is general enough to include asymmetric primary pattern illumination. The scalar and vector solutions are derived from the same initial equation so that the approximations used in obtaining the scalar solution are clearly displayed. Results from the vector and scalar theories are compared and the range of validity of the approximate analysis is indicated.

A new series representation for the radiation integral with application to reflector antennas

Abstract: Given the true or any approximate current on a reflector, the radiated far-field is determined from a rapidly convergent series representation of the radiation integral. The leading term is a well-shaped J_{1}(x)/x beam pointing in a desired direction. Higher order terms provide perturbations to the leading term. The coefficients of the series are independent of the observation angles. Hence, once they are computed, the field may be determined very rapidly at large numbers of points. Initially, a suitable small angle approximation is made that places the radiation integral in the form of a Fourier transform on a circular disk. The theory is then extended such that the results are valid in both the near and the wide angle regions. Application to a rotationally symmetric paraboloid is presented herein. Other applications include the offset and dual reflectors and near- to far-field integrations. A modified form of the series can also be used for Fresnel zone computations.

An efficient technique for the computation of vector secondary patterns of offset paraboloid reflectors

Abstract: A series approach for the rapid computation of the vector secondary pattern of offset paraboloid reflectors wherein the feed is displaced is presented. We show that the Jacobi polynomial series method, which has been demonstrated to provide an efficient means for evaluating the radiation integral of symmetric paraboloid reflectors, can be extended to the case of an offset paraboloid without compromising the ease or speed of computation. The analysis leading to the series formula is also useful for deriving an analytic expression for the optimum scan plane for the displacement of the feed. Representative numerical results illustrating the application of the method and the properties of the offset paraboloid are presented.

Phased Arrays for Radio Astronomy, Remote Sensing, and Satellite Communications

Abstract: Discover a modern approach to the analysis, modeling and design of high sensitivity phased arrays. Network theory, numerical methods and computational electromagnetic simulation techniques are uniquely combined to enable full system analysis and design optimization. Beamforming and array signal processing theory are integrated into the treatment from the start. Digital signal processing methods such as polyphase filtering and RFI mitigation are described, along with technologies for real-time hardware implementation. Key concepts from interferometric imaging used in radio telescopes are also considered. A basic development of theory and modeling techniques is accompanied by problem sets that guide readers in developing modeling codes that retain the simplicity of the classical array factor method while incorporating mutual coupling effects and interactions between elements. Combining current research trends with pedagogical material suitable for a first-year graduate course, this is an invaluable resource for students, teachers, researchers, and practicing RF/microwave and antenna design engineers.

Full-sampling array feeds for radio telescopes

Abstract: Phased array feeds offer the possibility of more efficient use of large radio astronomy reflector antennas by providing more closely spaced beams over a wide field of view and higher aperture efficiency in each beam than have been realized with horn feeds. This paper examines the array design constraints imposed by complete sampling of the fields near the reflector focus. In particular, array element spacing must be less than 1 (lambda) for large F/D reflectors and less than about 0.7 (lambda) for F/D < 0.5. This rules out conventional horns as array elements and sets a limit on the array bandwidth. The receive-only case of radio astronomy permits the use of number of signal combining techniques that do not degrade system sensitivity. Because practical arrays are of finite extent, and unwanted noise from the antenna surroundings is largely coherent between the elements, neither field conjugate nor maximal-ratio diversity methods of array weight optimization can be used. A modified form of field matching is a good starting approximation, however. Correction of reflector errors is examined briefly.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.