共查询到20条相似文献，搜索用时 96 毫秒
1.
A general analysis of phased array noise properties and measurements, applied to one square meter tiles of the Thousand Element Array (THEA), has resulted in a procedure to define the noise budget for a THEA-tile (Woestenburg and Dijkstra, 2003). The THEA system temperature includes LNA and receiver noise, antenna connecting loss, noise coupling between antenna elements and other possible contributions. This paper discusses the various noise contributions to the THEA system temperature and identifies the areas where improvement can be realized. We will present better understanding of the individual noise contributions using measurements and analysis of single antenna/receiver elements. An improved design for a 1-m2 Low Noise Tile (LNT) will be discussed and optimized low noise performance for the LNT is presented. We will also give future perspectives of the noise performance for such tiles, in relation to the requirements for SKA in the 1 GHz frequency range. 相似文献
2.
Y. Doi S. Makiuti H. Okuda T. Nakagawa H. Shibai M. Kawada N. Hiromoto M. Fujiwara K. Okumura 《Experimental Astronomy》2000,10(2-3):393-401
We have developed a 4 × 8 array of stressed Ge:Ga detectors. This array detector has a high density format ofentrance pupils so that we can minimize the size of the cameraoptics. The cutoff wavelength of the detector is about 170 m, and the detector's NEP is better than 1016 WHz-1/2. We are going apply this array detector toballoon-borne astronomical observations. Furthermore, we aredeveloping this detector into a 5 × 15 array detector that will be placed onboard the IRIS satellite to be launched in 2003. 相似文献
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Short dipoles are a key element in new low frequency array antennas as proposed for LOFAR and other astronomical applications. Unfortunately standard texts on short dipole antennas are based on the effective area and do not lead to an astronomically useful sensitivity formulation in a straightforward manner. The concept of maximum effective area is applied to arrays of short dipoles and allows expressing the sensitivity as the ratio of this area over the effective sky brightness temperature as long as the output noise power is dominated by the antenna input radiation. For both quantities we only need to know the array directivity pattern that includes the mutual coupling effects when the actual loading conditions of the array elements are taken into account. Short dipole elements have a constant directivity pattern for frequencies below resonance, but they exhibit strong complex impedance variations that provide only narrow band performance when power matching is applied as required in transmit applications. However, in receive applications voltage or current sensing can be realized, for example with an active balun. Assisted by the steep increase of the sky brightness with wavelength for frequencies below 300 MHz, this can provide sky noise dominated performance over at least a three to one frequency range. Still the low frequency limit is determined by the amplifier noise contribution and the losses in the antenna and in the dielectric ground surrounding the elements. We show that for a sparse array with the elements non-uniformly distributed according to an exponential shell model, a constant sensitivity can be obtained over a frequency range of at least two octaves. In addition, such a configuration has a factor of six greater sensitivity than a rectangular array for a large part of the frequency band. 相似文献
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The initial test station (ITS) is the first full scale prototype of a low frequency array (LOFAR) station. It operates in the 10–40 MHz range and consists of 60 sky noise limited dipoles arranged in a five-armed spiral structure offering an instantaneous synthesized aperture of almost 200 m diameter. We will present all sky snapshot images demonstrating sky-noise limited imaging capability in the presence of a strong RFI source that exceeds the all sky power by 27 dB. This result is obtained with a two stage self-calibration procedure. First, the RFI source near the horizon is used as calibrator and then subtracted, after which Cas A shows up at a level that is a factor 2000 lower and then dominates the picture with its side lobes. A second self calibration on Cas A then reveals the same extended galactic emission as found in a RFI free adjacent spectral channel. This demonstrates that a single 10 kHz channel of a 6.7 s snapshot of a single LOFAR station already provides a dynamic range of over 104. 相似文献
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A. Van Ardenne P. N. Wilkinson P. D. Patel J. G. Bij De Vaate 《Experimental Astronomy》2004,17(1-3):65-77
ASTRON has demonstrated the capabilities of a 4 m2, dense phased array antenna (Bij de Vaate et al., 2002) for radio astronomy, as part of the Thousand Element Array project (ThEA). Although it proved the principle, a definitive answer related to the viability of the dense phased array approach for the SKA could not be given, due to the limited collecting area of the array considered. A larger demonstrator has therefore been defined, known as “Electronic Multi-Beam Radio Astronomy Concept”, EMBRACE, which will have an area of 625 m2, operate in the band 0.4–1.550 GHz and have at least two independent and steerable beams. With this collecting area EMBRACE can function as a radio astronomy instrument whose sensitivity is comparable to that of a 25-m diameter dish. The collecting area also represents a significant percentage area (∼10%) of an individual SKA “station.” This paper presents the plans for the realisation of the EMBRACE demonstrator. 相似文献
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The CdZnTe array detector is a new type of semiconductor detector being rapidly developed in recent years. It possesses a high spatial resolution and a high energy resolution, and it can work at room temperatures. This paper describes the physical properties and working principle of the CdZnTe array detector, as well as the manufacturing technology, including the chip pretreatment, passivation, ohmic electrode preparation, array template selection, and array packaging technology (micro-interconnection). For evaluating the perfor-mance of the detector, the authors have developed successfully a 4 pixel×4 pixel CdZnTe array and an 8 pixel×8 pixel CdZnTe array (with the thicknesses of 5 mm and 2 mm, the pixel size of 2 mm×2 mm, and the gaps of 0.15 mm and 0.2 mm, respectively) in cooperation with the partner. A multi-channel electronic readout system based on the ASIC (Application Specific Integrated Circuit) chip is devel-oped independently for the charge measurement of the 4 pixel×4 pixel CdZnTe array. The energy spectra and corresponding energy resolutions of the 16 pixels are obtained with the 137Cs radiative source, among them the best resolution is 4.8%@662 kev. 相似文献
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N. Udaya Shankar K. Golap S. Sachdev R. Dodson M. Katwaroo Ch.V. Sastry 《Astrophysics and Space Science》2002,282(1):15-28
The Mauritius Radio Telescope (MRT) has been built with the main objective of surveying the southern sky at meter wavelengths.
MRT is a Fourier synthesis, T-shaped non-coplanar array. It consists of a2048 m long East-West arm with 1024 fixed helices
and a 880 m long South arm with 15 trolleys. Each trolley has four helices. A 512 channel, 2-bit 3-level complex correlation
receiver is used to process the data from the EW and S group outputs. At least 60 days of observing are required for obtaining
the Fourier components of the brightness distribution of the sky required to complete the survey. The MRT survey will be one
of the most extensive survey at low frequencies providing a moderately deep radio catalog reaching a source density of about
2 × 104 sr-1 over most of the sky south of δ=-10°with an angular resolution of 4' × 4.6' sec (δ) and a limiting flux density of 200 mJy (3 σ level) at 151 MHz. This paper
will describe the telescope, the observations carried out so far, challenges of imaging with the data acquired over a period
exceeding four years with a non-coplanar array, and summarises the results obtained so far.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
一种扩大FAST视场的方法 总被引：1，自引：0，他引：1
所有的大口径射电望远镜都存在这样一个问题：在其分辨率和灵敏度提高的同时，视场变小．而且口径越大，视场越小．这成为大口径望远镜不可回避的矛盾．要解决这个矛盾，可以在望远镜的焦平面上放置Ⅳ个分立馈源．让它们同时工作，这样可以看作把视场扩大了Ⅳ倍．望远镜的工作效率提高Ⅳ倍．但是这样做的缺点是——视场不连续．且馈源数目Ⅳ受到望远镜焦比(F／D)的限制．采用致密焦面阵(dense focal plane array)就可以很好地解决这个问题．致密焦面阵的单元不是喇叭口天线，而是无方向性的Vivaldi天线(Vivaldi antenna)．要把Vivaldi阵列应用到望远镜上，需要对单个Vivaldi天线和Vivaldi阵列的电性能有清楚的认识，并能根据需要来设计照明方向图．还要知道大望远镜的焦面上电磁场的分布情况，借此判断能否应用Vivaldi阵列，以及给出Vivaldi单元的分路赋权网络．主要给出了FAST的焦面场的分布情况．并说明应用Vivaldi阵列的可能性． 相似文献
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As part of the NASA Space Infrared telescope Facility (SIRTF), a low noise multiplexer has been developed. The hybridization of this multiplexer to a high indium antimonide (InSb) photodiode array has resulted in a MWIR detector of outstanding performance. The multiplexer is made of a 256×256 array of source follower amplifiers on a 30 m square pitch. Random access binary decoders are used to access each pixel of the array, allowing any read-out scheme to be implemented. Dark current has been measured at temperatures ranging from 4K to 77K. Generation recombination currents dominate above 45K. With 100mV of reverse bias applied, less than 3×10-17 A is typical below 50K with 8×10-19 A (5 e-/s) at 4K. Under the same conditions 0.25 pA was measured at 77K. Read noise has been measured as low as 186 e- using non-correlated techniques. Detector QE is 50 to 80 % through the entire 1 to 5 m band. 相似文献
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D. Enard 《Astrophysics and Space Science》1989,160(1-2):45-53
The ESO Very Large Telescope project consists of an array of four 8-m telescopes. This concept presents a very great flexibility and covers a broad range of scientific applications. The most far reaching one is the co-phasing of the four telescopes which will open the way to very high resolution imaging.The funding has been granted in December 1987. The first telescope is scheduled for 1995. The whole array is expected to be completed by the 2000.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988. 相似文献
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射电望远镜一般要在宽频段内进行连续观测, 但传统相控阵天线设计方法难以兼顾宽频带和大角度扫描特性. 紧耦合天线的设计方法为宽带大角度扫描天线提供了新的设计思路, 基于此设计了一款宽带双极化 Vivaldi相控阵馈源. 首先结合Wheeler提出的连续电流片概念及等效电路对紧耦合原理进行理论分析, 然后针对Vivaldi天线分析了阵元间的强耦合能够有效拓展天线的工作带宽. 在此基础上设计了一款宽带Vivaldi相控阵馈源. 馈源阵列由8×9 Vivaldi天线阵元组成, 该阵列的工作带宽为2-8GHz, 并且能够在E面和H面均实现±$45^\circ$的扫描特性. 最后对该馈源阵列进行了样机加工和测试, 测试结果与仿真结果具有较好的一致性. 相似文献
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Zhen Wang Yiqing Guo Hui Cai Jinfan Chang Tianlu Chen Danzengluobu Youliang Feng Qi Gao Quanbu Gou Yingying Guo Chao Hou Hongbo Hu Labaciren Cheng Liu Haijin Li Jia Liu Maoyuan Liu Bingqiang Qiao Xiangli Qian Xiangdong Sheng Zhen Tian Qun Wang Liang Xue Yuhua Yao Shaoru Zhang Xueyao Zhang Yi Zhang 《Experimental Astronomy》2018,45(3):363-377
A scintillation detector array composed of 115 detectors and covering an area of about 20000 m2 was installed at the end of 2016 at the Yangbajing international cosmic ray observatory and has been taking data since then. The array is equipped with electronics from Large High Altitude Air Shower Observatory Square Kilometer Complex Array (LHAASO-KM2A) and, in turn, currently serves as the largest debugging and testing platform for the LHAASO-KM2A. Furthermore, the array was used to study the performance of a wide field-of-view air Cherenkov telescope by providing accurate information on the shower core, direction and energy, etc. This work is mainly dealing with the scintillation detector array. The experimental setup and the offline calibration are described in detail. Then, a thorough comparison between the data and Monte Carlo (MC) simulations is presented and a good agreement is obtained. With the even-odd method, the resolutions of the shower direction and core are measured. Finally, successful observations of the expected Moon’s and Sun’s shadows of cosmic rays (CRs) verify the measured angular resolution. 相似文献
16.
H. Watarai K. Chaen H. Matsuhara T. Matsumoto H. Takahashi 《Experimental Astronomy》1994,3(1-4):179-180
A liquid helium cooled mid-infrared imaging Fabry-Perot spectrometer has been under development. A Si:P 5×5 detector array is used for this instrument. Although the array system has small format, but combination with JFET array will provide noise equivalent line flux of 1.0×10-21
W/cm
2 (1000sec, 10). This sensitivity is comparable with the SWS of the ISO. 相似文献
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Gert Finger Frank Eisenhauer Reinhard Genzel Christopher Mandla Ian Baker Domingo Alvarez Antonio Amorim Wolfgang Brandner Christophe Dupuy Casey Deen Derek Ives Leander Mehrgan Manfred Meyer Karin Perraut Guy Perrin Jörg Stegmeier Christian Straubmeier Harald J. Weller Vincent Isgar 《Astronomische Nachrichten》2023,344(8-9):e20230069
Near-infrared adaptive optics as well as fringe tracking for coherent beam combination in optical interferometry require the development of high-speed sensors. Because of the high speed, a large analog bandwidth is required. The short exposure times result in small signal levels which require noiseless detection. Both requirements cannot be met by state-of-the-art conventional CMOS technology of near-infrared arrays as has been attempted previously. A total of five near-infrared SAPHIRA 320 × 256 pixel HgCdTe e−APD arrays have been deployed in the wavefront sensors and in the fringe tracker of the VLTI instrument GRAVITY. The current limiting magnitude for coherent exposures with GRAVITY is mk = 19, which is made possible with ADP technology. New avalanche photo-diode array (APD) developments since GRAVITY include the extension of the spectral sensitivity to the wavelength range from 0.8 to 2.5 μm. After GRAVITY a larger format array with 512 × 512 pixels has been developed for both AO applications at the ELT and for long integration times. Since dark currents of <10−3 e−/s have been demonstrated with 1Kx1K e−APD arrays and 2Kx2K e−APD arrays have already been developed, the possibilities and adaptations of e−APD technology to provide noiseless large-format science-grade arrays for long integration times are also discussed. 相似文献
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Abstract— Silica aerogel collector tiles have been employed for the collection of particles in low Earth orbit and, more recently, for the capture of cometary particles by NASA's Stardust mission. Reliable, reproducible methods for cutting these and future collector tiles from sample return missions are necessary to maximize the science output from the extremely valuable embedded particles. We present a means of macroscopic subdivision of collector tiles by generating large‐scale cuts over several centimeters in silica aerogel with almost no material loss. The cut surfaces are smooth and optically clear allowing visual location of particles for analysis and extraction. This capability is complementary to the smaller‐scale cutting capabilities previously described (Westphal 2004; Ishii 2005a, 2005b) for removing individual impacts and particulate debris in tiny aerogel extractions. Macroscopic cuts enable division and storage or distribution of portions of aerogel tiles for immediate analysis of samples by certain techniques in situ or further extraction of samples suited for other methods of analysis. The capability has been implemented in the Stardust Laboratory at NASA's Johnson Space Center as one of a suite of aerogel cutting methods to be used in Stardust sample curation. 相似文献
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Measurements of the lateral distribution function (ldf) of Extensive Air Showers (EAS) as recorded by the array of water-
erenkov detectors at Haverah Park are described, and accurate experimental parameterizations expressing the mean ldf for 2 × 1017 < E < 4 × 1018 eV, 50 < r < 700 m, and θ < 45° are given. An extrapolation of these relations to the regime E ≥ 1019 eV and r > 700 m is described: extrapolation in this energy domain appears valid, and an approximate correction term is given for the larger core distances. The results of recent Monte Carlo simulations of shower development and detector behavior are compared to the parameterized ldf. The agreement is good increasing confidence that these simulations may be trusted as design tools for the Auger project, a proposed ‘next generation’ detector system. 相似文献