China
Africa
Explore chapters and articles related to this topic
Introductory Material
Published in Ronald L. Snell, Stanley E. Kurtz, Jonathan M. Marr, Fundamentals of Radio Astronomy, 2019
Ronald L. Snell, Stanley E. Kurtz, Jonathan M. Marr
In 1932 Karl JanskyJansky, Karl detected radio signals serendipitously from an extraterrestrial source, marking the beginning of the field of radio astronomy. Although Jansky deduced that the radio signals originated from beyond the solar system, more than two decades passed before we understood that the origin of this emission was due largely to synchrotron emission produced by high energy cosmic ray electrons interacting with the magnetic field of the Milky Way. The field of radio astronomy has advanced significantly since those early days, and observations at radio wavelengths today play a vital role in the study of astronomical objects ranging from solar system bodies to distant quasars. In the first volume of the Fundamentals of Radio Astronomy, we addressed how radio telescopes function and the methods used to make observations. In this second volume, we discuss what we can learn about the astrophysics of the Universe from radio wavelength observations.
Low Noise Amplifiers
Published in Krzysztof Iniewski, Wireless Technologies, 2017
Leonid Belostotski, James Haslett
CMOS LNAs are now common in many commercial applications from global positioning system (GPS) to UWB systems that do not require extraordinarily low noise figures. The CMOS implementations are very common in these applications and allow for high levels of integration and low product costs. Radio astronomy, on the contrary, can only tolerate very little of added noise due to extremely low signal levels received by the radio telescopes. All radio telescope designers implement LNAs made of exotic and expensive materials, such as GaAs and InP high electron mobility transistors (HEMTs), that add very little noise. For a telescope that requires only a handful of LNAs, the price advantage of MOSFET is overshadowed by the performance advantage of HEMT.
Telescopes
Published in Daniel Malacara-Hernández, Brian J. Thompson, Fundamentals and Basic Optical Instruments, 2017
Marija Strojnik, Maureen S. Kirk
At about the same time that we learned that mosaicking a mirror surface is beneficial to light collection but not necessarily to the resolution, we also discovered the detrimental effects of the atmosphere. The need to phase segmented mirrors brought into focus the application of interferometry for the detection of a specific feature in the spatial frequency domain. The spatial frequency domain corresponds to the space where a Fourier transform of the irradiance distribution is presented. Thus, it has been known for a long time that two separated apertures give information about one spatial frequency. This spatial frequency corresponds to the inverse separation between the apertures, along the line connecting the apertures. By changing the separation of the apertures, also referred to as the interferometer baseline, a continuous set of spatial frequencies could be sampled. The interferometry has been used since the 1950s in radio astronomy to synthesize the shape of radio sources, using a set of spatially separated radiation collecting mirror segments.
Optimal design of electromagnetic metamaterial electronic device sensor with specific performance based on multivariate big data fusion
Published in Journal of Experimental Nanoscience, 2023
Electromagnetic metamaterials also have a wide range of applications in the terahertz band (0.1 Thz–10 Thz). Terahertz wave is a fairly wide range of electromagnetic radiation between millimetre wave and infrared wave, terahertz wave is also known as T-ray, also known as sub-millimetre wave, it has great application prospects in physics, material science, medical imaging, radio astronomy, broadband and secure communication, especially in the communication between satellites. For a long time, the lack of effective methods for generating and detecting THZ radiation, as well as few materials in nature that can respond to this band, has led to the ‘THZ gap’ in the electromagnetic spectrum. At the same time, compared with microwave technology and optoelectronics technology, THZ technology has made slow progress, and functional THZ wave devices, such as filters, switches, modulators, phase shifters and beam control devices, are still unable to be applied [25].
A Comparative Study of Nature-Inspired Metaheuristic Algorithms in Search of Near-to-optimal Golomb Rulers for the FWM Crosstalk Elimination in WDM Systems
Published in Applied Artificial Intelligence, 2019
The OGRs play an important role in a variety of real-world applications including radio frequency allocation, sensor placement in X-ray crystallography, computer communication network, pulse phase modulation, circuit layout, geographical mapping, self-orthogonal codes, VLSI architecture, coding theory, linear arrays, fitness landscape analysis, radio astronomy, antenna design for radar missions, sonar applications and NASA missions in astrophysics, planetary and earth sciences (Babcock 1953; Bloom and Golomb 1977; Blum, Biraud, and Ribes 1974; Cotta and Fernández 2005; Dimitromanolakis 2002; Dollas, Rankin, and McCracken 1998; Fang and Sandrin 1977; Lam and Sarwate 1988; Lavoie, Haccoun, and Savaria 1991; Memarsadegh 2013; Project Educational NASA Computational and Scientific Studies (enCOMPASS) 0000; Rankin 1993; Robinson and Bernstein 1967; Soliday, Homaifar, and Lebby 1995).
Microscopic damage behavior in carbon fiber reinforced plastic laminates for a high accuracy antenna in a satellite under cyclic thermal loading
Published in Advanced Composite Materials, 2018
Satoshi Kobayashi, Tomoaki Shimpo, Ken Goto
A large antenna on orbit is useful equipment for the field of radio astronomy and communication technologies. As a higher accuracy antenna reflector, a deployable reflector composed by tensioned radial ribs and circumferential cable structure build on a truss structure were proposed [1]. Under space environment, variation in temperature, for example, solar irradiation and eclipse, causes cyclic thermal deformation of the structure, which reduces accuracy of the geometry and resultant resolution of the antenna. In order to overcome this situation, carbon-fiber-reinforced plastics (CFRP) are expected as a candidate material. Coefficient of thermal expansion (CTE) of carbon fiber is less than 0. Thus zero CTE of CFRP laminate could be attained if an appropriate laminate configuration is designed. On the other hand, in the laminate, mismatch in the thermal expansion coefficients between plies with different fiber orientations causes thermal stress which becomes the main reason for transverse matrix cracking. Moreover, cyclic temperature variation causes cyclic thermal stress condition. Therefore, it is very important to clarify microscopic damage development in CFRP laminates under thermal cycling in the view of the practical use because such damages affect mechanical properties of CFRP, such as elastic modulus [2].