共查询到20条相似文献，搜索用时 203 毫秒
1.
超宽带接收机面临众多技术挑战,而关键技术难点之一是超宽带低噪声放大器.采用以砷化镓材料为基底的70 nm栅长改性高电子迁移率晶体管和双电源偏置4级放大电路结构,设计了一款4–40 GHz超宽带低噪声单片微波集成放大器,完整覆盖C、X、Ku、K、Ka共5个波段.设计仿真结果表明,该放大器增益为(40±2.5) dB,常温下噪声温度平均95 K, 4–12.5 GHz噪声温度全频带低于83 K,直流功耗130.5 mW.整个频带内输入反射系数典型值-10 d B,输出反射系数典型值-15 d B,全频带范围内稳定,无自激振荡现象.该器件可做为前置放大器,应用于超宽带接收机和大规模多波束接收机中,可有效提高射电望远镜观测效率. 相似文献
2.
文中所作的主要工作是为云南天文台十米抛物面设计、制造一付好的对数周期偶极子天线（ＬＰＤＡ）作馈源。工作有：（１）设计一对交叉的ＬＰ－ＤＡ；（２）分析ＬＰＤＡ特性；（３）估算抛物面的电特性；（４）讨论线极化向园极化转换的问题；（５）天线测量。ＬＰＤＡ的测量结果比较满意。该天线的方向图、平均输入阻抗、三分贝和十分贝波瓣宽度都在从０．５－１．５ＧＨｚ的频率范围内比较一致和稳定，变化很小。天线理论上的许多成就都是与数子计算机有关的。在文中，我们充分利用了计算机的功能来设计天线，分析天线特性，并从测量所得的所有数据文件中计算天线的参数。所编ＦＯＲＴＲＡＮ程序使这一切工作变得容易。最后，我们还讨论了用功率合成器实现线极化向园极化转换的各种情况 相似文献
3.
作为射电天文接收机系统的关键器件, 低噪声放大器的噪声和增益性能对接收机系统的灵敏度有重要影响. 采用100nm砷化镓赝配高电子迁移率晶体管(pseudomorphic High Electron Mobility Transistor, pHEMT)\lk工艺, 研制了一款可覆盖C波段(4--8GHz)的低噪声放大器(Low Noise Amplifier, LNA). 所设计的LNA采用3级共源级联放大拓扑结构, 栅极、漏极双电源供电. 常温下测试表明, 该LNA在4--8GHz频段内平均噪声温度为\lk60K, 在5GHz处获得最低噪声温度50K, 通带内增益($31\pm1.5$)dB, 输入输出回波损耗均优于10dB, 芯片面积为$2.1\times1.1$mm2, 可以应用于C波段射电天文接收机以及卫星通信系统等. 相似文献
4.
M. Bersanelli E. Mattaini E. Santambrogio A. Simonetto S. Cirant F. Gandini C. Sozzi N. Mandolesi F. Villa 《Experimental Astronomy》1998,8(3):231-238
We have produced a prototype broadband, low-sidelobe conical corrugated feed horn suitable for measurements of the Cosmic Microwave Blackground (CMB) radiation in the frequency band 120–150 GHz. The antenna is a first prototype for the Low Frequency Instrument array in ESA's PLANCK mission, a space project dedicated to CMB anisotropy mesurements in the 30–900 GHz range. We describe the fabrication method, based on silver electro-formation, and present the two-dimensional antenna beam pattern measured at 140 GHz with a milimeter-wave automated scalar test range. The beam has good symmetry in the E and H planes with a far sidelobe level approaching –60 dB at angles 80°. An upper limit to the return loss was measured to be –21 dB. 相似文献
5.
为检测微弱的射电信号,要求望远镜接收机噪声性能良好.低噪声放大器(Low Noise Amplifier, LNA)作为接收机前端关键电路,其噪声系数和增益决定了整机的噪声性能.设计了一款1.2–2.2 GHz的低噪声放大器,电路采用两级级联结构,第2级通过引入负反馈,在改善增益平坦度和拓宽带宽的同时减小噪声,级间经过后级输入阻抗优化后仅需一个隔直电容.并引入有损输出匹配网络,实现高增益、低噪声、良好回波损耗和较为平坦的宽带LNA设计.测试结果表明,在1.2–2.2 GHz频段增益30–33 dB,噪声温度平均值为47 K,输出1 d B压缩点大于11.3 dBm.测试性能良好,可用于该频段接收机系统中. 相似文献
6.
The new 0.8?–?2.0 GHz Ond?ejov radio spectrograph with high time resolution (10 ms) is presented. As an example of first observations the 0.95?–?1.3 GHz narrowband pulsating structure with a characteristic quasi-period of about 150 ms, observed during the impulsive phase of the 9 June 2007 M1.0 flare, is shown. Some of the pulses show very fast but measurable frequency drift of about ?17 GHz s?1. The model of this pulsating structure, based on the tearing and coalescence processes in the current sheet, is briefly discussed. 相似文献
7.
8.
R. A. Kandalyan 《Astrophysics》2005,48(1):99-110
Radio observations with the VLA-A radio telescope of 30 OH megamaser galaxies at a frequency of 1.49 GHz are discussed. Radio emission was detected from all 30 of these galaxies. Radio emission was detected from 5 of the 30 objects for the first time. Important results were obtained for 12 galaxies that had previously been little studied in the radio continuum. Additional data at 1.49 GHz were obtained for the remaining 13 objects. The core component of the continuum radio emission predominates in the OH megamaser galaxies.Translated from Astrofizika, Vol. 48, No. 1, pp. 125–138 (February 2005). 相似文献
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10.
On 13 December 2006, some unusual radio bursts in the range 2.6?–?3.8 GHz were observed during an X3.4 flare/CME event from 02:30 to 04:30 UT in active region NOAA 10930 (S06W27) with the digital spectrometers of the National Astronomical Observatories of China (NAOC). During this event many spikes were detected with the high temporal resolution of 8 ms and high frequency resolution of 10 MHz. Many of them were found to have complex structures associated with other radio burst types. The new observational features may reflect certain emission signatures of the electron acceleration site. In this paper, we present the results of the analysis of the new observational features of the complex spikes. According to the observed properties of the spikes, we identify five classes. Their observational parameters, such as duration, bandwidth, and relative bandwidth, were determined. Most spikes had negative polarization, but spikes with positive polarization were observed during a short time interval and were identified as a separate class. Based on the analysis of observations with Hinode/SOT (Solar Optical Telescope) we suggest that the sources of the spikes with opposite polarizations were different. Combined observations of spikes and fiber bursts are used to estimate the magnetic field strength in the source. 相似文献
11.
Masato Naruse Tetsuya Ito Yutaro Sekimoto Hiroyuki Toba Naohisa Satou Masahiro Sugimoto Wenlei Shan Yoshizou Iizuka Toshiaki Kamba Mamoru Kamikura Yasutaka Serizawa 《Experimental Astronomy》2009,24(1-3):89-107
We have developed a near-field vector beam measurement system covering the range of frequencies from 385 to 500 GHz. The measurement set-up is capable of measurements with dynamic range exceeding 50 dB and amplitude and phase stability respectively of 0.1 dB/h and 1 degree/5 min at room temperature. Beam patterns of the ALMA band 8 corrugated horns and receiver optics block were measured at room temperature and lately compared with physical optics calculations obtained in the far-field. Both co-polar and cross-polar beam patterns of a qualification model of the ALMA band 8 cartridge cooled in a cartridge-test-cryostat have also been measured in the near-field as a detector of a submillimeter vector network analyzer. The measurements presented in this work refer to the lowest, middle and upper frequencies of band 8. The comparisons between software model and experimental measurements at these frequencies show good agreement down to ?30 dB for the main polarization component. The cross-polarization level of the beam propagating through the receiver optics block was also characterized. We found that a cross-polarization level better than ?28 dB can be achieved at all measured frequencies. The measured beam pattern of this receiver corresponds to efficiency of greater than 92% at the sub reflector (diameter of 750 mm) of the ALMA 12 m optics. 相似文献
12.
Andrew H. Jaffe 《New Astronomy Reviews》2004,48(11-12):1483
We discuss the ability of the SKA to observe QSO proper motions induced by long-wavelength gravitational radiation. We find that the SKA, configured for VLBI with multiple beams at high frequency (8 GHz), is sensitive to a dimensionless characteristic strain of roughly 10−13, comparable to (and with very different errors than) other methods in the 1/yr frequency band such as pulsar timing. 相似文献
13.
Arnold O. Benz Christian Monstein Michael Beverland Hansueli Meyer Bruno Stuber 《Solar physics》2009,260(2):375-388
A new multichannel spectrometer, Phoenix-3, is in operation having capabilities to observe solar flare radio emissions in the 0.1?–?5 GHz range at an unprecedented spectral resolution of 61.0 kHz with high sensitivity. The present setup for routine observations allows measuring circular polarization, but requires a data compression to 4096 frequency channels in the 1?–?5 GHz range and to a temporal resolution of 200 ms. First results are presented by means of a well observed event that included narrowband spikes at 350?–?850 MHz. Spike bandwidths are found to have a power?–?law distribution, dropping off below a value of 2 MHz for full width at half maximum (FWHM). The narrowest spikes have a FWHM bandwidth less than 0.3 MHz or 0.04% of the central frequency. The smallest half-power increase occurs within 0.104 MHz at 443.5 MHz, which is close to the predicted natural width of maser emission. The spectrum of spikes is found to be asymmetric, having an enhanced low-frequency tail. The distribution of the total spike flux is approximately an exponential. 相似文献
14.
N. S. Meshalkina A. T. Altyntsev D. A. Zhdanov S. V. Lesovoi A. A. Kochanov Y. H. Yan C. M. Tan 《Solar physics》2012,280(2):537-549
The analysis of narrowband drifting of type III-like structures in radio bursts dynamic spectra allows one to obtain unique information about the primary energy release mechanisms in solar flares. The SSRT (Siberian Solar Radio Telescope) spatially resolved images and its high spectral and temporal resolution allow for direct determination not only of the source positions but also of the exciter velocities along the flare loop. Practically, such measurements are possible during some special time intervals when SSRT is observing the flare region in two high-order fringes near 5.7?GHz; thus, two 1D brightness distributions are recorded simultaneously at two frequency bands. The analysis of type III-like bursts recorded during the flare 14?April 2002 is presented. Using multiwavelength radio observations recorded by the SSRT, the Huairou Solar Broadband Radio Spectrometer (SBRS), the Nobeyama Radio Polarimeters (NoRP), and the Radio Solar Telescope Network (RSTN), we study an event with series of several tens of drifting microwave pulses with drift rates in the range from ?7 to 13?GHz?s?1. The sources of the fast-drifting bursts were located near the top of a flare loop in a volume of a few Mm in size. The slow drift of the exciters along the flare loop suggests a high pitch anisotropy of the emitting electrons. 相似文献
15.
正在发展中的云南天文台０．５ＧＨｚ—１．５ＧＨｚ快速射电频谱分析仪的接收天线部分是计划在现有的十米口径抛物面天线的焦点上安装两付互相垂直的对数周期偶极子天线作为馈源。本文介绍了设计一个ＦＯＲＴＲＡＮ语言程序对对数周期偶极子天线电特性进行分析的过程，它可以在整个工作频段范围内计算出任意频率点上一副对数周期偶极子天线两个主平面内的方向图、波瓣宽度、增益和输入阻抗，并把结果以数据文件的形式记录下来，结合绘图软件，就可给出直观的结果，从而为对数周期偶极子天线的设计方案提供了可靠的理论判据。本文最后针对为云南天文台抛物面所设计的馈源作具体的分析。 相似文献
16.
?brahim Kü?ük ?pek üler ?ükriye ?z Sedat Onay Ali R?za ?zdemir Mehmet Gül?en Mikail Sar?kaya Nazl? Derya Dag?tekin Ferhat Fikri ?zeren 《Experimental Astronomy》2012,33(1):1-26
Selecting the future site for a large Turkish radio telescope is a key issue. The National Radio Astronomy Observatory is now in the stage of construction at a site near Karaman City, in Turkey. A single-dish parabolic radio antenna of 30?C40 m will be installed near a building that will contain offices, laboratories, and living accommodations. After a systematic survey of atmospheric, meteorological, and radio frequency interference (RFI) analyses, site selection studies were performed in a predetermined location in Turkey during 2007 and 2008. In this paper, we described the experimental procedure and the RFI measurements on our potential candidate??s sites in Turkey, covering the frequency band from 1 to 40 GHz. 相似文献
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18.
The solar burst of 21 May, 1984, 13 26 UT, showed radio spectral emission with a turnover frequency above 90 GHz, well correlated in time with the hard X-ray emission. It consisted of seven major time structures (1–3 s in duration), of which each was composed of several fast pulses with rise times between 30 and 60 ms. The spectral indices of the millimeter and hard X-ray emission exhibited sudden changes during each major time structure. The subsecond pulses were nearly in phase at 30 and 90 GHz, but their relative amplitude at 90 GHz ( 50%) were considerably larger than at 30 GHz (<5%). It was also found that the 90 GHz and the 100 keV X-rays fluxes were proportional to the repetition rate of the subsecond pulses, and that the hard X-ray power law index hardens with increasing repetition rate.Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986. 相似文献
19.
Baolin Tan 《Solar physics》2008,253(1-2):117-131
From the observations with the Chinese Solar Broadband Radiospectrometer (SBRS/Huairou) in the frequency range of 1.10?–?2.06 GHz and 2.60?–?3.80 GHz during 2004?–?2006, we select 14 flare events which were associated with numerous fast microwave subsecond pulsating structures (period: P<0.5 s). In order to describe these subsecond pulsating structures comprehensively, we defined a set of observable parameters including emission frequency (f 0), bandwidth (b w), polarization degree (r), period (P), duration (D), modulation depth (M), quality factor (Q), single pulse frequency drifting rate (R spfd), global frequency drifting rate (R gfd), and symmetrical factor of the pulse profile (S). Then based on a detailed analysis of the spectrograms of the fast pulsations which occurred in one of these flares (an X3.4 flare/CME event occurred on 13 Dec. 2006), we discuss the possible relations among these observable parameters and their physical implications for the dynamical processes of solar eruptive events, and applied them to interpret the nature of the pulsations in the flare/CME event. Such study of microwave periodic pulsations provides us with a useful tool to probe the details of the flare kernels, and understand the physical mechanism of solar eruptive processes. 相似文献
20.
Yu. P. Ilyasov M. Imae Y. Hanado V. V. Oreshko V. A. Potapov A. E. Rodin M. Sekido 《Astronomy Letters》2005,31(1):30-36
We present the results from our timing of the millisecond pulsar B1937+21, performed jointly since 1997 on two radio telescopes: the RT-64 in Kalyazin (Russia) at a frequency of 0.6GHz and RT-34 in Kashima (Japan) at a frequency of 2.15 GHz. The rms value of the pulse time of arrival (TOA) residuals for the pulsar at the barycenter of the Solar system is 1.8 μs (the relative variation is ≈10?14 over the observing period). The TOA residuals are shown to be dominated by white phase noise, which allows this pulsar to be used as an independent time scale keeper. The upper limit for the gravitational background energy density Ωgh2 at frequencies ≈6.5 × 10?9 Hz is estimated to be no higher than 10?6. Based on the long-term timing of the pulsar, we have improved its parameters and accurately determined the dispersion measure and its time variation over the period 1984–2002, which was, on average, ?0.00114(3) pc cm?3 yr?1. 相似文献