Novel High Isolation Antennas for Simultaneous Transmit and Receive (STAR) Applications

Radio frequency (RF) spectrum congestion is a major challenge for the growing need of wireless bandwidth. Notably, in 2015, the Federal Communications Commission (FCC) auctioned just 65 MHz (a bandwidth smaller than that used for WiFi) for more than $40 billion, indicating the high value of the microwave spectrum. Current radios use one-half of their bandwidth resource for transmission, and the other half for reception. Therefore, by enabling radios to transmit and receive across their entire bandwidth allocation, spectral efficiency is doubled. Concurrently, data rates for wireless links also double. This technology leads to a new class of radios and RF frontends. Current full-duplex techniques resort to either time- or frequency-division duplexing (TDD and FDD respectively) to partition the transmit and receive functions across time and frequency, respectively, to avoid self-interference. But these approaches do not translate to spectral efficiency. Simultaneous transmit and receive (STAR) radios must isolate the transmitter from the receiver to avoid self-interference (SI). This SI prevents reception and must therefore be cancelled. Self-interference may be cancelled with one or more stages involving the antenna, RF or analog circuits, or digital filters. With this in mind, the antenna stage is the most critical to reduce the SI level and avoid circuit saturation and total system failure. This dissertation presents techniques for achieving STAR radios. The initial sections of the dissertation provide the general approach of stage to stage cancellation to achieve as much as 100 dB isolation between the receiver and transmitter. The subsequent chapters focus on different antennas to achieve strong transmit/receive isolation. As much as 35 dB isolation is shown using a new spiral antenna array with operation across a 2:1 bandwidth. Also, a new antenna feed is presented showing 42 dB isolation across a 250 MHz bandwidth. Reflections in the presence of a dynamic environment are also considered

The S2 VLBI Correlator: A Correlator for Space VLBI and Geodetic Signal Processing

We describe the design of a correlator system for ground and space-based VLBI. The correlator contains unique signal processing functions: flexible LO frequency switching for bandwidth synthesis; 1 ms dump intervals, multi-rate digital signal-processing techniques to allow correlation of signals at different sample rates; and a digital filter for very high resolution cross-power spectra. It also includes autocorrelation, tone extraction, pulsar gating, signal-statistics accumulation.Comment: 44 pages, 13 figure

The Apache Point Observatory Galactic Evolution Experiment (APOGEE)

The Apache Point Observatory Galactic Evolution Experiment (APOGEE), one of the programs in the Sloan Digital Sky Survey III (SDSS-III), has now completed its systematic, homogeneous spectroscopic survey sampling all major populations of the Milky Way. After a three-year observing campaign on the Sloan 2.5 m Telescope, APOGEE has collected a half million high-resolution (R ~ 22,500), high signal-to-noise ratio (>100), infrared (1.51–1.70 μm) spectra for 146,000 stars, with time series information via repeat visits to most of these stars. This paper describes the motivations for the survey and its overall design—hardware, field placement, target selection, operations—and gives an overview of these aspects as well as the data reduction, analysis, and products. An index is also given to the complement of technical papers that describe various critical survey components in detail. Finally, we discuss the achieved survey performance and illustrate the variety of potential uses of the data products by way of a number of science demonstrations, which span from time series analysis of stellar spectral variations and radial velocity variations from stellar companions, to spatial maps of kinematics, metallicity, and abundance patterns across the Galaxy and as a function of age, to new views of the interstellar medium, the chemistry of star clusters, and the discovery of rare stellar species. As part of SDSS-III Data Release 12 and later releases, all of the APOGEE data products are publicly available

Optical interferometry in astronomy

Here I review the current state of the field of optical stellar interferometry, concentrating on ground-based work although a brief report of space interferometry missions is included. We pause both to reflect on decades of immense progress in the field as well as to prepare for a new generation of large interferometers just now being commissioned (most notably, the CHARA, Keck and VLT Interferometers). First, this review summarizes the basic principles behind stellar interferometry needed by the lay-physicist and general astronomer to understand the scientific potential as well as technical challenges of interferometry. Next, the basic design principles of practical interferometers are discussed, using the experience of past and existing facilities to illustrate important points. Here there is significant discussion of current trends in the field, including the new facilities under construction and advanced technologies being debuted. This decade has seen the influence of stellar interferometry extend beyond classical regimes of stellar diameters and binary orbits to new areas such as mapping the accretion discs around young stars, novel calibration of the cepheid period-luminosity relation, and imaging of stellar surfaces. The third section is devoted to the major scientific results from interferometry, grouped into natural categories reflecting these current developments. Lastly, I consider the future of interferometry, highlighting the kinds of new science promised by the interferometers coming on-line in the next few years. I also discuss the longer-term future of optical interferometry, including the prospects for space interferometry and the possibilities of large-scale ground-based projects. Critical technological developments are still needed to make these projects attractive and affordable.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48845/2/r30503.pd

Instrumentation development of innovative radio-devices to improve the coming cycles of radio astronomy observations

Radio astronomy represents one of the most useful tools for investigating celestial objects such as sychrontronic emissions from quasar , molecular clouds in the interstellar medium, and a black hole event horizon . All this is possible due to the great sensitivity that astronomical receivers can achieve, and the high angular resolution that can be reached using interferometric techniques. However, despite the great effort made, radio astronomy is not exempt of limitations that prevent it from deploying its maximum capability in terms of resolution. Atmospheric phase fluctuations, mainly induced by turbulent currents, are primarily responsible. Failure to correct these phase fluctuations will impede that the maximum potential of radio astronomy can be realized. In this thesis work, a novel solution to solve the drawbacks related to phase fluctuations in high frequency observations is presented. The ALMA telescope in Chile , has been selected as a target. The idea is to use an external optical system at room temperature, which can illuminate a low and a high frequency receiver, simultaneously. In this way, the solution for the phase fluctuation can be transferred from low to high frequency, thus, extending the maximum baseline for interferometric observations at high frequencies

Radio & Infrared Observations of the W3/W4/W5 Star-forming Regions

As part of the Low Frequency Array (LOFAR) Surveys KSP, targeted observations of H II regions close to high mass star-forming regions in the Galactic plane have been conducted, as part of the telescope’s commissioning. This thesis details the calibration and analysis of one particular commissioning field, the prominent Galactic star-forming W3/W4/W5 complex and 2 supernova remnants (SNRs) HB3 and 3C 58, at unprecedented low radio frequencies ~ 30–76 MHz (§ 1). This part of the radio spectrum contains large-scale filaments, arcs, bubbles and shells which would be interesting to detail in new parameter space, both spatially and spectrally. A LOFAR calibration pipeline was developed as part of this work (§ 3) resulting in unique continuum maps ~10 deg2 that detail extended diffuse emission of W3/W4/W5 at unprecedented sensitivity and angular resolution at low frequencies. Our final full bandwidth image (at ~ 53.5 MHz) reaches a final resolution of between ~ 62–85" and noise level of 4.78 mJy/beam, making it the deepest image obtained in this frequency range. Spectral index maps (§ 4) made from 35.2 MHz, 54.7 MHz and 69.9 MHz continuum images give strong evidence of radio emission by thermal Bremsstrahlung with some localised regions demonstrating free-free self-absorption (§ 2), although we suspect a complete turnover of the H II regions outside of our observed range ɑ ~ -0.03±0.02 for 3C 58 and observe a possible plateau in the emission of HB3 near ~ 55 MHz. High spectral resolution data was also analysed for the possibility of a carbon RRL detection in absorption < 100 MHz in the direction of W3 (§ 5). An initial all-sky image was also made during the commissioning of the Chilbolton LOFAR single station (§ 3); the wide FoV gave an overview of the large-scale diffuse Galactic synchrotron emissivity with the intention of measuring the spectral index High mass star formation is an important area of research in modern astrophysics and triggers of this process along with many of the aspects of early stellar evolution including the onset of maser emission being poorly understood. Stars form out of large gas and dust clouds, detected through: (i) thermal dust continuum emission and (ii) line emission of organic molecules traced through masers. Hence, ancillary observations of W3 were made using the Onsala 20m radio viii telescope for maser source detection and a point source catalogue of ~ 1300 sources at far-IR wavelengths of predominantly cold proto-stars was made from the newest AKARI maps (§ 6).Finally, in addition to the Galactic diffuse radio emission, ~ 300 extragalactic point sources were captured in the background of the FoV with LOFAR. Their extracted fluxes were catalogued and over ~ 50 % provided a rich sample of spectral index information to constrain turnover of synchrotron < 100 MHz. We observed strong and moderate SED flattening attributed to free-free absorption processes at the source for ~ 3.2 % and ~ 19.1 % of sources respectively which is consistent with Rafferty et al. (2013)

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion

The Cosmic 21-cm Revolution Charting the first billion years of our universe

The redshifted 21-cm signal is set to transform astrophysical cosmology, bringing a historically data-starved field into the era of Big Data. Corresponding to the spin-flip transition of neutral hydrogen, the 21-cm line is sensitive to the temperature and ionization state of the cosmic gas, as well as to cosmological parameters. Crucially, with the development of new interferometers it will allow us to map out the first billion years of our universe, enabling us to learn about the properties of the unseen first generations of galaxies. Rapid progress is being made on both the observational and theoretical fronts, and important decisions on techniques and future direction are being made. The Cosmic 21-cm Revolution gathers contributions from current leaders in this fast-moving field, providing both an overview for graduate students and a reference point for current researchers