Wavefront Correction for Large, Flexible Antenna Reflector

A wavefront-correction system has been proposed as part of an outer-space radio communication system that would include a large, somewhat flexible main reflector antenna, a smaller subreflector antenna, and a small array feed at the focal plane of these two reflector antennas. Part of the wavefront-correction system would reside in the subreflector, which would be a planar patch-element reflectarray antenna in which the phase shifts of the patch antenna elements would be controlled via microelectromechanical systems (MEMS) radio -frequency (RF) switches. The system would include the following sensing-and-computing subsystems: a) An optical photogrammetric subsystem built around two cameras would estimate geometric distortions of the main reflector; b) A second subsystem would estimate wavefront distortions from amplitudes and phases of signals received by the array feed elements; and c) A third subsystem, built around small probes on the subreflector plane, would estimate wavefront distortions from differences among phases of signals received by the probes. The distortion estimates from the three subsystems would be processed to generate control signals to be fed to the MEMS RF switches to correct for the distortions, thereby enabling collimation and aiming of the received or transmitted radio beam to the required precision

Design and Performance of a Wideband Radio Telescope

The Goldstone Apple Valley Radio Telescope (GAVRT) is an outreach project, a partnership involving NASA's Jet Propulsion Laboratory (JPL), the Lewis Center for Educational Research (LCER), and the Apple Valley Unified School District near the NASA Goldstone deep space communication complex. This educational program currently uses a 34-meter antenna, DSS12, at Goldstone for classroom radio astronomy observations via the Internet. The current program utilizes DSS12 in two narrow frequency bands around S-band (2.3 GHz) and X-band (8.45 GHz), and is used by a training program involving a large number of secondary school teachers and their classrooms. To expand the program, a joint JPL/LCER project was started in mid-2006 to retrofit an additional existing 34-meter beam-waveguide antenna, DSS28, with wideband feeds and receivers to cover the 0.5-to- 14-GHz frequency bands. The DSS28 antenna has a 34-meter diameter main reflector, a 2.54-meter subreflector, and a set of beam waveguide mirrors surrounded by a 2.43-meter tube. The antenna was designed for high power and a narrow frequency band around 7.2 GHz. The performance at the low end of the frequency band desired for the educational program would be extremely poor if the beam waveguide system was used as part of the feed system. Consequently, the 34-meter antenna was retrofitted with a tertiary offset mirror placed at the vertex of the main reflector. The tertiary mirror can be rotated to use two wideband feeds that cover the 0.5-to-14-GHz band. The earlier designs for both GAVRT and the DSN only used narrow band feeds and consequently, only covered a small part of the S- and X-band frequencies. By using both a wideband feed and wideband amplifiers, the entire band from 0.5 to 14 GHz is covered, expanding significantly the science activities that can be studied using this system

Hypercube matrix computation task

A major objective of the Hypercube Matrix Computation effort at the Jet Propulsion Laboratory (JPL) is to investigate the applicability of a parallel computing architecture to the solution of large-scale electromagnetic scattering problems. Three scattering analysis codes are being implemented and assessed on a JPL/California Institute of Technology (Caltech) Mark 3 Hypercube. The codes, which utilize different underlying algorithms, give a means of evaluating the general applicability of this parallel architecture. The three analysis codes being implemented are a frequency domain method of moments code, a time domain finite difference code, and a frequency domain finite elements code. These analysis capabilities are being integrated into an electromagnetics interactive analysis workstation which can serve as a design tool for the construction of antennas and other radiating or scattering structures. The first two years of work on the Hypercube Matrix Computation effort is summarized. It includes both new developments and results as well as work previously reported in the Hypercube Matrix Computation Task: Final Report for 1986 to 1987 (JPL Publication 87-18)

A aquisição de linguagem/libras e o aluno surdo: um estudo sobre as formas de comunicação e interação na escola e na família

A aquisição de linguagem e de Libras pelo aluno surdo nos anos iniciais do Ensino Fundamental ainda é pouco estudado no meio acadêmico. Esta pesquisa tem o objetivo de analisar as estratégias didáticas, linguísticas e de interação utilizadas pelo profissional intérprete de Libras na atuação em sala de aula e pelo professor bilíngue surdo na Sala de Recursos Multifuncionais-SRM, da Rede Municipal de Dourados, MS. Os objetivos específicos foram os seguintes: discutir a proposta e a prática de educação do surdo no estado de Mato Grosso do Sul, tendo como foco principal o município de Dourados; investigar as formas de interação do professor bilíngue, do intérprete de Libras e da família para com o aluno surdo; analisar as estratégias didáticas, as possibilidades, os avanços e os desafios na atuação do professor bilíngue na Sala de Recursos Multifuncionais-SRM e dos intérpretes de Libras no contexto da sala de aula. Fundamentado na perspectiva dos Estudos Surdos e da teoria do Desenvolvimento Humano Ecológico de Bronfenbrenner, o estudo teve como metodologia a análise documental, a observação em sala de aula, as entrevistas com o professor surdo, com os intérpretes educacionais e com as famílias. Os resultados indicaram que os alunos surdos chegam à escola sem o domínio de uma língua de comunicação; que há baixa frequência ao Atendimento Educacional Especializado; que apenas uma professora de Libras divide sua atuação entre duas Salas de Recursos em escolas polo; que os alunos que não frequentam as SRMs aprendem Libras exclusivamente por meio do intérprete em sala de aula, no momento da tradução e interpretação. Os impasses para a educação detectados foram a falta de materiais adaptados e o pouco uso de recursos visuais por parte dos professores. Os principais desafios relatados para a aquisição de linguagem/Língua de Sinais pelos alunos surdos na escola comum foram os que se seguem: criar estratégias para aumentar o tempo de exposição à Libras, prevenir ausências e promover a assiduidade ao AEE; proporcionar espaços para o uso da Libras no ambiente familiar; prover outras formas de interação com aluno surdos, com profissional bilíngue e comunidade surda no espaço educacional. Espera-se que as discussões aqui postas e as reflexões realizadas possam trazer contribuições para o redimensionamento dos serviços ofertados e melhoria para o processo de aquisição de Linguagem/Libras, assim como o desenvolvimento do processo de aprendizagem dos alunos surdos no contexto escolar e familiar

DSS-28: a novel wide bandwidth radio telescope devoted to educational outreach

We have recently equipped the 34-meter DSS-28 radio telescope at the Goldstone Deep Space Communications Complex with a novel wide bandwidth radiometer and digital signal processor as part of the Goldstone Apple Valley Radio Telescope (GAVRT) educational outreach program operated by the Jet Propulsion Laboratory and the Lewis Center for Educational Research. The system employs a cryogenically cooled wide bandwidth quad-ridge feed and InP low noise amplifiers to achieve excellent noise performance from 2.7 to 14 GHz; a fractional bandwidth better than 4:1. Four independently tunable dual-polarization receivers each down-convert a 2 GHz block to baseband, providing access to 8 GHz of instantaneous bandwidth. A flexible FPGA-based signal processor has been constructed using CASPER FPGA hardware and tools to take advantage of this enormous bandwidth. This system demonstrates many of the enabling wide bandwidth technologies that will be crucial to maximizing the utility of future large centimeter-wavelength arrays, in particular the Square Kilometer Array. The GAVRT program has previously used narrow bandwidth total power radiometers to study flux variability of quasars and the outer planets. The versatility of DSS-28 will enable other projects including spectroscopy and SETI. Finally, the wide instantaneous bandwidth available makes this system uniquely suited for studying transient radio pulses. A configuration of the digital signal processor has been developed which provides the capability of recording a burst of raw baseband voltage data triggered by a real-time incoherent dedispersion system which is very sensitive to pulses from a known source, such as the Crab Nebula pulsar

Faster Antenna Noise Temperature Calculations Using a Novel Approximation Technique

In order to properly tradeoff the various antenna and feed configurations for the Square Kilometre Array (SKA) optical design it is necessary to evaluate the gain and noise temperature of each configuration over a wide range of frequencies. German Cortes describes the standard technique for computing antenna noise temperature. However, since the total antenna pattern needs to be calculated over the entire 4 pi steradians at a fine enough resolution to accurately include the main beam, the computer time required is enormous. Even at modest frequencies and reflector sizes (approximately 5 to 10 GHz for a 12 meter main reflector) the technique can take days on a single node of a supercomputer. Utilizing the standard technique to compute the noise temperature for all the cases required to properly characterize the SKA design is clearly not feasible. At least a 100 to 1000 speedup in the computation time is required. This paper describes an approximation technique that can accomplish this improvement with extremely small errors in noise temperature calculation of a few tenths of Kelvin

Performance of a Quad-Ridged Feed in a Wideband Radio Telescope

A new quad-ridged, flared horn achieving nearly constant beamwidth and excellent return loss over a 6:1 frequency bandwidth is described. The system performance in two Radio Telescopes: 1) A 12-meter symmetric dual shaped reflector system intended for geodetic very long baseline interferometry and 2) A 15-meter offset dual shaped reflector intended for the SKA is presented showing it to be excellent wideband feed choice

Performance of a quad-ridged feed in a wideband Radio Telescope (EuCAP 2011)

A new quad-ridged, flared horn achieving nearly constant beamwidth and excellent return loss over a 6:1 frequency bandwidth is described. The system performance in two Radio Telescopes: 1) A 12-meter symmetric dual shaped reflector system intended for geodetic very long baseline interferometry and 2) A 15-meter offset dual shaped reflector intended for the SKA is presented showing it to be excellent wideband feed choice

The quadruple-ridged flared horn: A flexible, multi-octave reflector feed spanning f/0.3 to f/2.5

In this paper, we present four quadruple-ridged flared horn designs achieving 6:1 frequency bandwidth with good match and near-constant beamwidth in E- and D-planes. Nominal 10 dB beamwidths of the designs range from 32 to 115 degrees. Such design flexibility makes the quad-ridge horn a very attractive reflector antenna feed candidate, especially for next generation radio telescopes