Search

The Five-hundred-meter Aperture Spherical radio Telescope (FAST), the largest single dish radio telescope in the world, has implemented an innovative technology for its huge reflector, which changes the shape of the primary reflector from spherical to that of a paraboloid of 300 m aperture. Here we explore how the current FAST sensitivity can potentially be further improved by increasing the illuminated area (i.e., the aperture of the paraboloid embedded in the spherical surface). Alternatively, the maximum zenith angle can be increased to give greater sky coverage by decreasing the illuminated aperture.Different parabolic apertures within the FAST capability are analyzed in terms of how far the spherical surface would have to move to approximate a paraboloid. The sensitivity of FAST can be improved by approximately 10 % if the aperture of the paraboloid is increased from 300 m to 315 m. The parabolic aperture lies within the main spherical surface and does not extend beyond its edge. The maximum zenith angle can be increased to approximately 35 degrees from 26.4 degrees, if we decrease the aperture of the paraboloid to 220 m. This would still give a sensitivity similar to the Arecibo 305 m radio telescope. Radial deviations between paraboloids of different apertures and the spherical surfaces of differing radii are also investigated. Maximum zenith angles corresponding to different apertures of the paraboloid are further derived. A spherical surface with a different radius can provide a reference baseline for shape-changing applied through active reflector technology to FAST-like telescopes., Accepted by MNRAS

The event rate, energy distribution, and time-domain behaviour of repeating fast radio bursts (FRBs) contains essential information regarding their physical nature and central engine, which are as yet unknown. As the first precisely-localized source, FRB 121102 has been extensively observed and shows non-Poisson clustering of bursts over time and a power-law energy distribution. However, the extent of the energy distribution towards the fainter end was not known. Here we report the detection of 1652 independent bursts with a peak burst rate of 122~hr^{-1}, in 59.5 hours spanning 47 days. A peak in the isotropic equivalent energy distribution is found to be ~4.8 x 10^{37} erg at 1.25~GHz, below which the detection of bursts is suppressed. The burst energy distribution is bimodal, and well characterized by a combination of a log-normal function and a generalized Cauchy function. The large number of bursts in hour-long spans allow sensitive periodicity searches between 1 ms and 1000 s. The non-detection of any periodicity or quasi-periodicity poses challenges for models involving a single rotating compact object. The high burst rate also implies that FRBs must be generated with a high radiative efficiency, disfavoring emission mechanisms with large energy requirements or contrived triggering conditions., 69 pages, 14 figures, 2 tables; Updates for author correction

FAST is designed, developed, manufactured and constructed by Chinese scientists. It took 22 years from the pilot study in 1994 to its completion in 2016. Its design and construction witnessed three major independent and endogenous innovations.

While looking up to the sky, humans always wondering who we are, where we come from and whether we are alone. In the vast universe, are there other civilizations? For thousands of years, man has merely observed the universe through the visible spectrum, while the radiation from celestial bodies covers the entire electromagnetic spectrum.

With the receiving area of approximately 30 soccer fields, the 500-m aperture FAST will maintain its status as the world-class equipment in the next 10–20 years. As it has been completed and put into operation, it will provide opportunities for astronomical development.

The Five-hundred-meter Aperture Spherical Telescope, or the FAST for short, known as the “China Sky Eye”, is the world’s largest and most sensitive single aperture radio telescope. It is located in a karst depression in Pingtang County, Qiannan Buyei and Miao Autonomous Prefecture, Guizhou Province.

RX J1301.9+2747 is an ultrasoft active galactic nucleus (AGN) with unusual X-ray variability that is characterized by a long quiescent state and a short-lived flare state. The X-ray flares are found to recur quasi-periodically on a timescale of 13-20 ks. Here, we report the analysis of the light curve in the quiescent state from two XMM observations spanning 18.5 years, along with the discovery of a possible quasi-periodic X-ray oscillation (QPO) with a period of ~1500s. The QPO is detected at the same frequency in the two independent observations, with a combined significance of >99.89%. The QPO is in agreement with the relation between frequency and black hole mass (M_BH) that has been reported in previous works for AGNs and Galactic black hole X-ray binaries (XRBs). The QPO frequency is stable over almost two decades, suggesting that it may correspond to the high-frequency type found in XRBs and originates, perhaps, from a certain disk resonance mode. In the 3:2 twin-frequency resonance model, our best estimate on the M_BH range implies that a maximal black hole spin can be ruled out. We find that all ultrasoft AGNs reported so far display quasi-periodicities in the X-ray emission, suggesting a possible link on the part of the extreme variability phenomenon to the ultrasoft X-ray component. This indicates that ultrasoft AGNs could be the most promising candidates in future searches for X-ray periodicities., 6 pages, 3 figures and 4 supplementary figures, to appear in A&A Letters

Fast radio bursts (FRBs) are cosmic sources that emit millisecond-duration radio pulses with a wide range of luminosities and yet unknown origin(s) (Petroff et al. 2019; cordes et al. 2019). A subset of FRBs were found to repeat, the prototype of which is the first precisely-located FRB 121102 (Spitler et al. 2016), residing in a dwarf galaxy at redshift z=0.193 (Chatterjee 2017; Tendulkar et al. 2017). The source has been observed by most major telescopes and shows non-Poisson clustering of bursts over time, the hitherto highest burst rate, and a burst isotropic equivalent energy largely consistent with a power-law (Law et al. 2017; zhang et al. 2018; Gourdji et al. 2019), all of which are crucial characteristics to be compared to non-repeating sources. However, due to sensitivity limits, no true energy distribution of any FRB is known. Here we report the detection of 1652 independent bursts, more than quadruple the total of all previously published ones combined, in a total of 59.5 observing hours spanning 47 days using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The peak burst rate of 122 hr-1is by far the highest ever observed of any FRB. A characteristic peak in the isotropic equivalent energy distribution is found to be ~4.8×1037 erg at 1.25 GHz, suggesting a possible threshold for producing abundant coherent radio bursts from FRBs. The burst energy distribution is optimally described by a bimodal distribution consisting of a log-normal function plus a Cauchy function. While no periodicity was found between 1 ms and 1000 s, and the majority of the burst arrival times are consistent with being random, there exists a visible peak in the waiting time distribution at about 3.4 ms, corresponding to significant clustering. Our results start to reveal the stochastic nature of abundant weaker bursts, which could be present in other FRB sources, apparently repeating or not. FRB generation mechanisms must be efficient and economical. Expensive triggers and/or contrived conditions for burst production seem unlikely.

We report the discovery of a highly dispersed fast radio burst, FRB~181123, from an analysis of $\sim$1500~hr of drift-scan survey data taken using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulse has three distinct emission components, which vary with frequency across our 1.0--1.5~GHz observing band. We measure the peak flux density to be $>0.065$~Jy and the corresponding fluence $>0.2$~Jy~ms. Based on the observed dispersion measure of 1812~cm$^{-3}$~pc, we infer a redshift of $\sim 1.9$. From this, we estimate the peak luminosity and isotropic energy to be $\lesssim 2\times10^{43}$~erg~s$^{-1}$ and $\lesssim 2\times10^{40}$~erg, respectively. With only one FRB from the survey detected so far, our constraints on the event rate are limited. We derive a 95\% confidence lower limit for the event rate of 900 FRBs per day for FRBs with fluences $>0.025$~Jy~ms. We performed follow-up observations of the source with FAST for four hours and have not found a repeated burst. We discuss the implications of this discovery for our understanding of the physical mechanisms of FRBs., 7 pages, 3 figures, accepted for publication in ApJL

The construction of FAST telescope was completed in Guizhou province of China in September 2016, and a kind of novel high-stability 48-core bendable and movable optical cable was developed and applied in analog data optical transmission system of FAST. Novel structure and selective material of this optical cable ensure high stability of optical power in the process of cables round-trip motion when telescope is tracking a radio source. The 10 5 times bend and stretch accelerated experiment for this optical cable was implemented, and real-time optical and RF signal power fluctuation were measured. The physical structure of optical cables after 10 5 times round-trip motion is in good condition; the real-time optical power attenuation fluctuation is smaller than 0.044 dB; the real-time RF power fluctuation is smaller than 0.12 dB. The optical cable developed in this letter meets the requirement of FAST and has been applied in FAST telescope.

Radio astronomy receiver development is focusing on increasing the field of view and bandwidth in tandem with the exponential increase in data volumes permitted by signal processing. We present recent receiver and signal processing developments from CSIRO and FAST.

We describe PSR J1926-0652, a pulsar recently discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Using sensitive single-pulse detections from FAST and long-term timing observations from the Parkes 64-m radio telescope, we probed phenomena on both long and short time scales. The FAST observations covered a wide frequency range from 270 to 800 MHz, enabling individual pulses to be studied in detail. The pulsar exhibits at least four profile components, short-term nulling lasting from 4 to 450 pulses, complex subpulse drifting behaviours and intermittency on scales of tens of minutes. While the average band spacing P3 is relatively constant across different bursts and components, significant variations in the separation of adjacent bands are seen, especially near the beginning and end of a burst. Band shapes and slopes are quite variable, especially for the trailing components and for the shorter bursts. We show that for each burst the last detectable pulse prior to emission ceasing has different properties compared to other pulses. These complexities pose challenges for the classic carousel-type models., Comment: 13pages with 12 figures

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) is expected to complete its commissioning in 2019. FAST will soon begin the Commensal Radio Astronomy FasT Survey(CRAFTS), a novel and unprecedented commensal drift scan survey of the entire sky visible from FAST. The goal of CRAFTS is to cover more than 20000 $deg^{2}$ and reach redshift up to about 0.35. We provide empirical measurements of the beam size and sensitivity of FAST across the 1.05 to 1.45 GHz frequency range of the FAST L-band Array of 19-beams(FLAN). Using a simulated HI-galaxy catalogue based on the HI Mass Function(HIMF), we estimate the number of galaxies that CRAFTS may detect. At redshifts below 0.35, over $6\, \times \, 10^{5}$ HI galaxies may be detected. Below the redshift of 0.07, the CRAFTS HIMF will be complete above a mass threshold of $10^{9.5}\,M_{\odot}$. FAST will be able to investigate the environmental and redshift dependence of the HIMF to an unprecedented depth, shedding light onto the missing baryon and missing satellite problems., Comment: Published as Sci. China-Phys. Mech. Astron. 62, 959506 (2019)

This paper reports on the time and frequency standard system for the Five-hundred meter Aperture Spherical radio Telescope (FAST), including the system design, stability measurements and pulsar timing observations. The stability and drift rate of the frequency standard are calculated using 1-year monitoring data. The UTC-NIM Disciplined Oscillator (NIMDO) system improves the system time accuracy and stability to the level of 5 ns. Pulsar timing observations were carried out for several months. The weighted RMS of timing residuals reaches the level of less than 3.0 μs.

We report the discovery of a binary millisecond pulsar (namely PSR J1641+3627F or M13F) in the globular cluster M13 (NGC 6205) and timing solutions of M13A to F using observations made with the Five-hundred-metre Aperture Spherical radio Telescope (FAST). PSR J1641+3627F has a spin period of 3.00 ms and an orbital period of 1.4 days. The most likely companion mass is 0.16 M$_{\odot}$. M13A to E all have short spin periods and small period derivatives. We also confirm that the binary millisecond pulsar PSR J1641$+$3627E (also M13E) is a black widow with a companion mass around 0.02 M$_{\odot}$. We find that all the binary systems have low eccentricities compared to those typical for globular cluster pulsars and that they decrease with distance from the cluster core. This is consistent with what is expected as this cluster has a very low encounter rate per binary., 12 pages, 9 figures, accepted for publication in ApJ

The Search for Extraterrestrial Intelligence (SETI) attempts to address the possibility of the presence of technological civilizations beyond the Earth. Benefiting from high sensitivity, large sky coverage, an innovative feed cabin for China's Five-hundred-meter Aperture Spherical radio Telescope (FAST), we performed the SETI first observations with FAST's newly commisioned 19-beam receiver; we report preliminary results in this paper. Using the data stream produced by the SERENDIP VI realtime multibeam SETI spectrometer installed at FAST, as well as its off-line data processing pipelines, we identify and remove four kinds of radio frequency interference(RFI): zone, broadband, multi-beam, and drifting, utilizing the Nebula SETI software pipeline combined with machine learning algorithms. After RFI mitigation, the Nebula pipeline identifies and ranks interesting narrow band candidate ET signals, scoring candidates by the number of times candidate signals have been seen at roughly the same sky position and same frequency, signal strength, proximity to a nearby star or object of interest, along with several other scoring criteria. We show four example candidates groups that demonstrate these RFI mitigation and candidate selection. This preliminary testing on FAST data helps to validate our SETI instrumentation techniques as well as our data processing pipeline., 21 pages, 19 figures, 3 tables, published in ApJ

Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a Chinese mega-science project to build the largest single dish radio telescope in Guizhou province, Southwest China. The construction of FAST will involve many kinds of analog and digital electrical equipments. The electrical equipments are potential threat to radio observation due to its ElectroMagnetic Interference (EMI) emission. The EMI should be safely shielded when FAST telescope operates. The shielding effectiveness of large shielding enclosures can be tested with two log periodic antennas, signal generator and spectrum analyzer. It is not suitable to test small shielding enclosure for that is not possible to put big antenna and signal generator inside. In this paper, an effective shielding effectiveness measurement system for the small shielding enclosure is introduced. This measurement system uses a frequency synthesizer of Valon Technology as signal generator which can measure the shielding effectiveness no more than 100dB in a frequency range of 23–6000MHz. Some of measurement results of shielding effectiveness are also presented.

The Square Kilometre Array (SKA) will be the world’s largest synthesis radio telescope, which is designed to answer major scientific questions such as those relating to the cosmic origin and fundamental forces in the universe. With the SKA entering into the phase of pre-construction, more than 100 institutes in about 20 countries including China have been involved in the associated key technology development. The Dish Verification Antenna China (DVA-C) is a concept prototype which has been built to meet the requirements of the SKA’s scientific goals. It utilizes a unique skin-and-rib structure with single-piece panel reflectors. This paper presents details on the design and measured performances of DVA-C, as well as the preliminary observational results. Current applications of the DVA-C are also introduced.

Phased array feeds (PAFs) for large diameter single dish radio telescopes offer the capability for multiple simultaneous beam formation and wide field-of-view surveys. An L-band PAF front end design is presented for the Five-hundred-meter Aperture Spherical Telescope (FAST), which is currently under construction and when complete will be the largest single dish radio telescope in the world. A broadband PAF element at L-band was designed in conjunction with the FAST optics and focal plane field distribution, fabricated, and tested. The simulated performance of the array meets the FAST PAF performance requirements for field of view, efficiency, sensitivity, and other key parameters. A unique aspect of the FAST PAF is the need for feed cabin vibration compensation. A study of the use of adaptive beamforming to compensate for lateral movement is given.

Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a Chinese mega-science project to build the largest single dish radio telescope in the world. The first light of FAST is expected in September 2016. Due to the high sensitivity of FAST, it is very sensitive to the radio frequency interference coming from the electrical and electronic equipments of telescope itself. In order to assure the realization of the scientific goals of the telescope, the electromagnetic compatibility (EMC) study on FAST at the design and construction stages, has been carried out to decrease the possibility of the interference from the telescope. Several examples, such as EMC designs and measurements for actuator and focus cabin, have been introduced briefly.

Phased array feed (PAF) is an emerging technology which can greatly improve the survey speed of telescopes. As a world-class radio telescope, the Five-hundred-meter Aperture Spherical radio Telescope (FAST) is also trying to enhance its observation capability and open up new scientific studies at several frequency bands by PAFs. At the first partof this paper, the blue print of the FAST PAFs development and corresponding scientific goals are introduced, as well as the progress has been made in these PAFs.

The SKA (Square Kilometer Array) will be the world’s largest synthesis radio telescope, which will address many fundamental questions about our universe. Scientists and Engineers from 67 institutions in 20 countries have joined the pre-study of the SKA since 1993. China has been playing an important role, from various SKA concepts in the early years, to the current site selection as well as the technical development. The SKA has now entered the pre-construction phase, and many countries including China are involved into the key technology development, such as antenna prototyping and Phased Array Feed. With China’s continuous participation into the SKA, including the establishment of a science team aiming at limited scientific objectives, technical studies and designs of high-precision light antennas and broadband wide-field receivers, the Chinese Astronomy and related technologies will be greatly promoted. The SKA will provide a great opportunity for China to play an active role in international mega-science projects.

A 500-m aperture spherical telescope (FAST) was funded by the National Development and Reform Commission of China (NDRC) in July 2007 and will be located in the unique Karst region, a sinkhole-like landform, in Guizhou province. FAST can be seen as a modified ldquoArecibordquo type radio telescope using many innovative techniques, with as much as twice the collecting area and a wider sky coverage. FAST has, first, an active reflector, conforming to a paraboloid of revolution from a sphere in real time through actuated control, which enables the realization of wide bandwidth and full polarization capability by using standard feed design. Secondly, it has a light focus cabin suspension system, integrating optical, mechanical, and electronic technologies, reducing effectively the cost of the support structure and control system. With such a huge collecting area of more than 30 football fields, FAST will become the largest single dish ever built. Here we will summarize the FAST concept and the milestones achieved in experiments on its key technologies, i.e., site exploration, active reflector prototyping, focus cabin driving mechanism, measurement and control techniques, and the receiver layout. The Miyun FAST demonstrator also will be presented.

A 12-pole wideband superconducting microstrip bandpass filter, which has a fractional bandwidth of 38% and a center frequency of 1455 MHz, is presented for the Miyun 50-m radio astronomy telescope, Beijing, China. A novel resonator, which can not only generate very large coupling, but also push its first spurious resonant peak away from the passband, is introduced. A new style interleaved coupling structure is proposed and successfully used in this study to realize the remarkably required strong coupling. To achieve high edge slope on the high side of the passband, as required, a single transmission zero was introduced. The filter was fabricated on a 36 mm times 30 mm times 0.5 mm double-sided YBa2Cu3O7 film deposited on an MgO substrate. The measured results showed that the filter had 0.05-dB minimum insertion loss, 0.08-dB passband ripple, and 23-dB return loss at a temperature of 40 K. The first spurious peak did not appear until 2632 MHz. The overall measured performance showed good agreement with the simulation.

This paper represents a low cost printed Vivaldi antenna at 3–10 GHz bandwidth for Radio telescope Feed system. The idea of this design is to minimize the number of telescope receivers for Square Kilometre Array (SKA) [1]. A minimized tapered slot antenna with a balun feed for receiver systems is proposed. The Vivaldi antenna is design on a relatively low dielectric constant substrate which operates at Ultra-Wideband (UWB). A typical tapered slot antenna is a combination of a wideband balun and a radiator with different tapering shapes such as linear, constant width, exponential and dual exponential. Two feeding configurations are used such as coplanar waveguide (CPW) to slot line transition and microstrip line to slotline transition [2–5]. The antenna modeling is analyzed using two different electromagnetic simulators such as HFSS and CST Microwave Studio. The results are shown that the antenna operates over a wide bandwidth extending from 3.1 to 10.6 GHz with a maximum gain of 7.3 dBi. Stable radiation patterns are observed across the operational bandwidth, with cross-polarization levels below −20 dB. The realized antenna structure occupies a volume of 45 × 45 × 0.5 mm3, and possesses the essential time domain fidelity needed for UWB Radio telescope Feed system applications. A prototype Vivaldi antenna is constructed and measured for validation. The Voltage Standing Wave Ratio (VSWR) of the proposed antenna is verified against the simulated data results, the measured and simulated results are found to be in good agreement. In particular, a good impedance bandwidth matching and stable directional radiation patterns were achieved across the operating frequency range. The combination of design aims and outcomes described in the paper indicates that the proposed antenna can be a suitable candidate for portable RF systems, or possible sensor element in an UWB antenna array application.

Stokes profile inversion is very important to get the information on the vector magnetic field. Because the magnetic fields cannot be directly observed, adopting Stokes spectrum analysis to obtain vector magnetic field has become the major technique recently. Therefore, by Stokes profile inversion, we obtained vector magnetic fields of two layers based on the numerical solution (DELO solution, ReEs et al., 1989) to the polarized radiative transfer equation. We analyze the relationships of sunspot magnetic field strength with sunspot area, umbral area and penumbra-umbra radius ratio. By statistical research, it is found that the field strengths of the upper layer and the lower one decrease with the increasing penumbra-umbra radius ratio, and that the logarithmic expression is able to fit well the relationship between the maximum field strength of the upper layer and the sunspot area. Furthermore, we verify the result obtained by Ringnes and Jensen (1961) about the relationship between the maximum magnetic field strength and the umbral area, and the result obtained by Antalova (1991) of the relationship between the field strength and the penumbra-umbra radius ratio.

The National Astronomical Observatories, Chinese Academy of Sciences is now building a 50 m radio telescope at the Miyun Station. In this paper, we give a brief introduction to the Miyun Station. The main specifications and the status of construction of the 50 m radio telescope are described. We are now building an L-band pulsar receiver for this new 50 m telescope. The status of this receiver project is also described. The 50 m telescope, together with the pulsar receiver, will make it a powerful radio telescope to carry out pulsar observations and researches in the near future.

FAST, Five hundred meter Aperture Spherical Telescope, is the Chinese effort for the international project SKA, Square Kilometer Array. An innovative engineering concept and design pave a new road to realizing huge single dish in the most effective way. Three outstanding features of the telescope are the unique karst depressions as the sites, the active main reflector which corrects spherical aberration on the ground to achieve full polarization and wide band without involving complex feed system, and the light focus cabin driven by cables and servomechanism plus a parallel robot as secondary adjustable system to carry the most precise parts of the receivers. Besides a general coverage of those critical technologies involved in FAST concept, the progresses in demonstrating model being constructed at the Miyun Radio Observatory of the NAOC is introduced. Being the most sensitive radio telescope, FAST will enable astronomers to jumpstart many of science goals, for example, the natural hydrogen line surveying in distant galaxies, looking for the first generation of shining objects, hearing the possible signal from other civilizations, etc. Among these subjects, the most striking one could be pulsar study. Large scale survey by FAST will not only improve the statistics of the pulsar population, but also may offer us a good fortune to pick up more of the most exotic, even unknown types like a sub-millisecond pulsar or a neutron star – black hole binary as the telescope is put into operation.

The influence of magnetic fields on the energy level populations of atoms is firstly studied by analysing the Stokes profiles of Fe I 6302.5 forming in the solar magnetized atmosphere, with the aid of a departure factor defined to evaluate the deviation from the normal Boltzmann distribution without a magnetic field. This factor is directly related to the ratio of line-source function to the continuum one. The relationship between the departure and the magnetic field reveals an effect that the magnetic field induces an exponential increase in the level population of the lower level of Fe I 6302.5 (Lande factor g = 2.5) with the field strength. This indicates that the magnetic field can cause the redistribution of populations of those levels whose Land e factors are non-zero. Therefore, this effect should be included in the calculation of the statistical equilibrium. Secondly, an experiment utilizing the Hg5461 line in the laboratory on the Earth is carried out to reveal that the exponential relation is independent of variations in temperature, and the excitation is completely magneto-induced. Finally, the exponential relation is explained by taking account of the magnetic energy in the Boltzmann distribution.

A novel wideband microstrip band-pass filter is presented in this letter based on a quadruple-mode ring resonator, which is developed by introducing a stepped-impedance one-wavelength ring resonator (SORR) into a stepped-impedance half-wavelength resonator (SHR). In order to suppress the harmonic responses of the filter for a wide stop-band, two band-stop sections with asymmetrical -type structure are introduced. A prototype filter having 49.3% of 1 dB and 57.9% of 3 dB fractional bandwidth is fabricated with advantages of high selectivity and high out-of-band rejection. In the pass-band, the return loss is larger than 18.8 dB and at the centre frequency insertion loss is 0.6 dB. The experiments are in good agreement with the simulations.

Since 1993, astronomers and engineers from more than 100 institutions in 20 different countries including China, have engaged in the international mega-science project—the Square Kilometre Array (SKA), which will be the world’s largest synthesis radio telescope. The SKA is currently in its pre-construction phase, and China has been playing a very active role. China has participated in 6 of the total of 10 SKA work packages, and carried out R&D in dish array, aperture array, wideband single pixel feeds, phased array feeds, signal and data transport, and science data processor. In the new SKA science book published in 2015, Chinese scholars have made their contributions in 20% of all the chapter proposals. After the SKA1 re-baselining, 20 Chinese astronomers participated in 11 out of the 13 SKA scientific working groups. The “2+1 Strategy” for China’s SKA science priorities has been established, and some important progress has been made in cosmological re-ionization detection as well as in SKA data processing. In June 2015, the Chinese participation in SKA1 passed through the Chinese Academy of Sciences Panel Review. The Chinese Community is now deeply involved into the preparation of the SKA, with activities such as SKA science cases study, researching on high-precision light-weight antennas, developing the Chinese prototype array, as well as some efforts in building an SKA regional data center in China. This article gives a brief historical review of the SKA, overviews some international and domestic progress of the project during its preconstruction phase, and also discusses some future plans of the Chinese SKA.

This paper presents a novel wideband microstrip band-pass filter for L-band low noise receiver of radio telescope. By introducing a stepped-impedance one-wavelength ring resonator (SORR) into a stepped-impedance half-wavelength resonator (SHR), excellent in-band performance is realized. In order to suppress the harmonic responses of the filter for a wide stop-band, two band-stop sections with asymmetrical π-type structure are designed. A prototype filter having 49.3% of 1-dB and 57.9% of 3-dB fractional bandwidth is fabricated with advantages of compact size, high selectivity and high out-of-band rejection. In the pass-band, return loss is less than −18.8dB and the minimal insertion loss is 0.6 dB.

A loop feed meander-line Antenna (LFMLA) RFID tag on a relatively low dielectric constant substrate operates on the European UHF band 865–868 MHz is presented. The tag modeling is analyzed using two different electromagnetic simulator HFSS and CST. A prototype tag antenna is constructed and measured for validation. The input impedance of the proposed antenna is verified against the simulated data results, the measured and simulated results are found to be in good agreement. The compact size tag antenna shows excellent impedance matching to the typical input impedance of a RFID integrated circuit chip and a significant improvement in reading range up to 5 meters.

The Effelsberg 100 m radio telescope has been used over a period of 5.5 yr to monitor the flux densities of 40 extragalactic radio sources. In this paper we study the long-term variability characteristics over timescales of several months of the quasar PKS 0528+134 at several wavelengths. It shows that the 6 cm light curve of the source hints at a time-asymmetric behavior as could be expected from an asymmetric source structure. The wavelength dependence of the degree of variability does not meet the predictions of the interstellar scintillation theory. Furthermore, variations of the spectral indices (α) follow the shock models. We conclude that the variations in PKS 0528+134 are probably intrinsic, and several intrinsic models are briefly discussed to interpret the observed variability properties.

We present results of MERLIN observations of five compact radio sources at 1.6 GHz, part of a large survey to identify compact symmetric objects (CSOs). We give for the first time MERLIN maps of two sources, 1604+315 and 1751+278. The five observed sources show very compact, unresolved point-like structure, which may imply that they axe good CSO candidates.

We present three epochs of VSOP observations of the BL Lac object2007+777 at 5 GHz. Compared with the ground-based VLBA data, the space baselines with HALCA clearly reveal a more detailed and finer source structure. Mainly based on the quite uniform and circular UV-coverages of the VLBA, and using a new cross-self calibration method, we have found evidence for weak structural changes on a timescale of two weeks in the core region of this intraday variable source. The physical causes for these variations are discussed.

We present 8 epochs of 7 mm dual-polarization VLBA observations of the gravitational lens system PKS 1830-211 made over the course of 14 weeks. Clear changes in the relative positions of the cores of up to 80 μarcseconds (μas) were observed between epochs (each separated by ≈2 weeks). A comparison with previous 7 mm VLBA maps shows that the separation of the cores has changed by almost 280 μas over 12 months. This leads us to conclude that changes in the brightness distribution of the mm-VLBI core of the background source must be occurring rapidly. This is the first clear observation of significant radio source evolution in a gravitational lens system. It is also the first time that changes in source structure have been detected in a distant extra-galactic source on such short time-scales. This is partly accounted for by the magnification provided by the lens system.

Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a Chinese mega-science project to build the largest single dish radio telescope in the world. The first light of FAST is expected in 2016. In order to protect the radio environment for FAST site, the local government has promised to establish a radio quiet zone of 30 km diameter, with the Dawodang depression in Guizhou province as the centre. The legislation of this radio quiet zone is underway.

Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a Chinese mega-science project to build the largest single dish radio telescope in the world. Its innovative engineering concept and design pave a new road to realize a huge single dish in the most effective way. FAST also represents Chinese contribution in the international efforts to build the square kilometer array (SKA). Being the most sensitive single dish radio telescope, FAST will enable astronomers to jump-start many science goals, for example, surveying the neutral hydrogen in the Milky Way and other galaxies, detecting faint pulsars, looking for the first shining stars, hearing the possible signals from other civilizations, etc. The idea of sitting a large spherical dish in a karst depression is rooted in Arecibo telescope. FAST is an Arecibo-type antenna with three outstanding aspects: the karst depression used as the site, which is large to host the 500-meter telescope and deep to allow a zenith angle of 40 degrees; the active main reflector correcting for spherical aberration on the ground to achieve a full polarization and a wide band without involving complex feed systems; and the light-weight feed cabin driven by cables and servomechanism plus a parallel robot as a secondary adjustable system to move with high precision. The feasibility studies for FAST have been carried out for 14 years, supported by Chinese and world astronomical communities. The project time is 5.5 years from the commencement of work in March of 2011 and the first light is expected to be in 2016. This review intends to introduce FAST project with emphasis on the recent progress since 2006. In this paper, the subsystems of FAST are described in modest details followed by discussions of the fundamental science goals and examples of early science projects., 36 pages, 28 figures, accepted for publication in International Journal of Modern Physics D