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The 28 papers in this special issue on antennas for next generation radio telescopes present state-of-the-art work being carried out at more than 20 institutions around the world in ten geographically dispersed countries. [ABSTRACT FROM AUTHOR]

Antenna noise temperature calculations of reflector systems is often a slow process and makes direct optimization of the sensitivity of these systems a difficult and time-consuming task. This paper presents an improvement to a recently proposed method to speed up these calculations by several orders of magnitude for large dish systems. The accuracy of the improved method is tested for several types of offset Gregorian systems, and errors are shown to be in the order of a few percent. Comparisons of several layers of simplification to a standard brightness temperature model are also presented to aid the designer in the choice of model complexity to use. [ABSTRACT FROM PUBLISHER]

In this study, a novel inset-fed slotted modified T-shape microstrip patch antenna with DGS is presented. This paper is a demonstration of Differential Algorithm (DE), which is used to optimize the various design parameters of slotted patch antenna in accordance with diverse necessities and scenarios, and also lowers the computation complexity of antenna. The proposed antenna design resonates in two different frequency bands, viz 11.13-11.82 and 15.77-16.89 GHz with their respective bandwidths of 690 and 1120 MHz resonating at 11.47 GHz and 16.27 GHz, respectively. These frequency bands have their application in the field of satellite broadcasting, aeronautical military systems, and radio astronomy corresponding to X and Ku band. The designed antenna has an overall small size of 20 × 11 mm2. The simulated and measured results for the proposed antenna with DE are presented and discussed further. [ABSTRACT FROM AUTHOR]

The far-field pattern of a geometrically large and complex antenna used in low-frequency radio astronomy is computationally expensive to simulate on electromagnetic simulators, such as FEKO. For example, one station of the Square Kilometer Array, which consists of 256 log-periodic antenna elements, will take years to simulate using the full CAD model for the full operational frequency band. This paper focuses on reducing the simulation time for a single antenna element by simplifying the simulation model, thus decreasing the number of unknowns that have to be solved in a simulation. An iterative process for optimizing the simplification of such an element is described, while keeping the reflection coefficient within 1 dB absolute mean deviation of the measured data. After four iterations, the amount of unknowns to be solved, which includes the number of triangles and segments, was reduced from 29,307 to 11,991. This decreased the computation time by 86.5%, making array simulations feasible. Using the techniques described in the paper, other antenna constructions can benefit from it and be simulated more efficiently. [ABSTRACT FROM AUTHOR]

In this paper, the results of reliability measurements and tests are presented. The systems taken into account concern two different architectures of a receiver chain for implementation in the Northern Cross Radiotelescope. A reliability analysis of the circuit and reliability tests implemented on critical parts of a fiber receiver chain were performed. The target was to chose the receiver chain with the highest value of mean time between failures and minimize faults in the structure. Moreover, since the reliability prediction indicated the front end, which was installed on the focal line of the antenna, as the more stressed block of the entire radioreceiver chain by environmental and climatic factors, we proposed specific development tests. The whole test plan has been characterized, and some results after a combination of temperature and humidity cycles, as well as random vibrations tests, are reported in this paper. The measurement and tests implemented in this paper for the solution of the receiver chain in the Northern Cross Radiotelescope can represent a useful aid for the new design of the international SKA project. [ABSTRACT FROM AUTHOR]

Large deployable antennas are required for the advancement of space communications, Earth observation, radio astronomy and deep space exploration. Most contemporary space antennas have exceeded the size of launching vehicles, leading to the necessity of stowed concepts to overcome the limitation. Many structural models have been investigated by different organizations. Generally, mesh deployable reflectors are currently more mature compared to other foldable solutions. This will be the topic of this paper. Orbital disturbances, perturbations originated by on-board sources and thermal deformations affecting the deployed configuration can deteriorate the accuracy of the communications system. Undesired dynamic behaviour of structural components has to be predicted and counteracted. Therefore, vibration control is a key technology to correct the distortions altering the proper functioning of the system. An intelligent active structure is introduced as a structure configured with distributed actuators and sensors and guided by a controller to modify the dynamic response of the system. In this paper, the supporting structure of a very large mesh reflector is described. A FEM formulation is adopted to assemble the frame and it is validated by comparing it with commercial codes. According to the adopted model, the active elements can be embedded in the middle of the truss elements. Of course, active control of all the devices at the same time requires a control effort which could be not affordable in space applications. However, the effectiveness is not the same for all the actuators. In this study, two cascade optimization procedures are performed to assess the best positioning and velocity feedback gains of the actuators that must be controlled to damp vibrations. In particular, a gradient-based technique is used after both a Genetic Algorithm and a Reinforcement Learning methodology to find the best set of gains for the controller. The objective function is set as a weighted sum of power consumption of the actuators. As a study case, the spacecraft implements a velocity feedback strategy when performing a generic attitude manoeuvre to coordinate the simultaneous action of the devices to ensure the damping performance of the system is enhanced. In addition, the impact of damaged actuators and uncertainties on the mechanical properties of the passive structure has been discussed and analysed. • Dynamics and control of large space structures. • Vibration suppression via smart materials. • Active truss-like structures modeling. • Genetic Algorithm and Reinforcement Learning methodology for optimization. • Robustness of the controller is verified by means Monte Carlo analysis. [ABSTRACT FROM AUTHOR]

The toolbox to study the Universe grew on 14 September 2015 when the LIGO–Virgo collaboration heard a signal from two colliding black holes between 30 and 250 Hz. Since then, many more gravitational waves have been detected as detectors continue to increase sensitivity. However, the current and future interferometric detectors will never be able to detect gravitational waves below a few Hz due to oceanic activity on Earth. An interferometric space mission, the laser interferometer space antenna, will operate between 1 mHz and 0.1 Hz, leaving a gap in the decihertz band. To detect gravitational-wave signals also between 0.1 and 1 Hz, the Lunar Gravitational-wave Antenna will use an array of seismic stations. The seismic array will be deployed in a permanently shadowed crater on the lunar south pole, which provides stable ambient temperatures below 40 K. A cryogenic superconducting inertial sensor is under development that aims for fm/ √ Hz sensitivity or better down to several hundred mHz, and thermal noise limited below that value. Given the 10 6 m size of the Moon, strain sensitivities below 10 − 20 1/ √ Hz can be achieved. The additional cooling is proposed depending on the used superconductor technology. The inertial sensors in the seismic stations aim to make a differential measurement between the elastic response of the Moon and the inertial sensor proof-mass motion induced by gravitational waves. Here, we describe the current state of research toward the inertial sensor, its applications, and additional auxiliary technologies in the payload of the lunar gravitational-wave detection mission. [ABSTRACT FROM AUTHOR]

In this letter, design and characterization of an antenna fabricated using the three‐dimensional star used in the epaulets of defense personnel are presented for its use in sub‐6 GHz 5G communication. Initially, the star antenna is designed and simulated using CST Microwave Studio by choosing its dimension in accordance with those in the epaulets. The star antenna is placed over a single‐sided copper‐clad substrate and is excited via a coaxial probe, where an attempt to achieve the optimum feed position is made via simulation. This is followed by simulation of a two‐star array antenna where the element separation commensurate with the arrangement as that on the epaulets. Subsequently, a single‐ and two‐star array antenna is fabricated and their return loss and free space radiation pattern measurements are carried out. Measured results reflect a good comparison with that of the simulated one. [ABSTRACT FROM AUTHOR]

This paper reports a design study for a space-based decametric wavelength telescope. While not a new concept, this design study focused on many of the operational aspects that would be required for an actual mission. This design optimized the number of spacecraft to insure good visibility of approx. 80% of the radio galaxies- the primary science target for the mission. A 5,000 km lunar orbit was selected to guarantee minimal gravitational perturbations from Earth and lower radio interference. Optimal schemes for data downlink, spacecraft ranging, and power consumption were identified. An optimal mission duration of 1 year was chosen based on science goals, payload complexity, and other factors. Finally, preliminary simulations showing image reconstruction were conducted to confirm viability of the mission. This work is intended to show the viability and science benefits of conducting multi-spacecraft networked radio astronomy missions in the next few years. [ABSTRACT FROM AUTHOR]

This paper describes the design and experimental behavior of a 2nd iterated modified Square Ring Shaped Fractal Antenna (SRSFA). The radiator geometry consists of three symmetrical square-shaped rings loaded with circular patterns at the corners. The designed fractal patch is placed on a slot loaded ground structure. The electrical dimensions possessed by the realized structure are 0.15λ 0 x 0.15λ 0 x 0.080 λ 0 , and the whole antenna is implemented using FR4 substrate. In this design, transmission line width 'W F ' and position 'F P ' are optimized using Shuffled Frog Leaping Algorithm (SFLA) and Artificial Bee Colony (ABC) strategies. It has been examined that the optimized values of 'W F ' and 'F P ' using SFLA and ABC are 2.6 and 12.4 mm, and 3.2 and 15.9 mm, respectively. Results reveal that SFLA offers better solution quality and convergence speed than ABC. Further, experimental analysis has been demonstrated to effectively illustrate the recommended fractal approach. The equivalent circuit of the designed structure is implemented successfully. The conducted measurements show that for VSWR ≤ 2, the fabricated structure produces six resonance points with adorable S11 values. The resonances appear at 1.53 GHz (1.35–1.67 GHz), 4.30 GHz (4.20–4.40 GHz), 7.58 GHz (7.43–7.70 GHz), 11.35 GHz (10.37–11.58 GHz), 14.03 GHz (13.85–14.35 GHz), and 15.93 GHz (15.43–16.25 GHz). The examined −10 dB impedance bandwidth at the respective resonance points is 20.9 %, 4.6 %, 3.5 %, 11.3 %, 2.9 %, and 5.23 %. Healthy concordance is noticed among the experimental measurements and electromagnetic simulations. The demonstrated radiation patterns are arbitrary bidirectional/omnidirectional at the respective resonances with good stability. Additionally, the offered gain is within the range of 4.91–7.00 dB. Hence, by utilizing the above-mentioned approaches, miniaturization of 65 % has been achieved. Practical outcomes suggest that the introduced prototype exhibiting multiband behavior, can be effectively applied in Radio location, Radio astronomy, Long-range tracking, Weather location Broadcasting, Search for extra-terrestrial intelligence, Radar altimeters, High resolution mapping, Aeronavigation, and Miscellaneous Radars. [ABSTRACT FROM AUTHOR]

LWA1 is a new radio telescope operating in the frequency range 10–88 MHz, located in central New Mexico. The telescope consists of 258 pairs of dipole-type antennas whose outputs are individually digitized and formed into beams. Simultaneously, signals from all dipoles can be recorded using one of the instrument's “all dipoles” modes, facilitating all-sky imaging. Notable features of the instrument include high intrinsic sensitivity (\approx\6 kJy zenith system equivalent flux density), large instantaneous bandwidth (up to 78 MHz), and four independently steerable beams utilizing digital “true time delay” beamforming. This paper summarizes the design of LWA1 and its performance as determined in commissioning experiments. We describe the method currently in use for array calibration, and report on measurements of sensitivity and beamwidth. [ABSTRACT FROM PUBLISHER]

This paper presents a new approach to reduce mutual coupling effects in large phased array antennas currently under development for use in low frequency radio astronomy. A receive mode definition of coupling between two antennas is shown to serve as a good indicator of the severity of mutual coupling interactions in a phased array. Thus, an efficient way to reduce mutual coupling in the array is to design antenna elements for low receive coupling. It is demonstrated that wire inverted-V dipole antennas can be designed with significantly reduced receive coupling over a wide range of frequencies and wave directions by proper selection of the antenna element geometry and feed impedance. Corresponding improvements in the performance of a large aperiodic phased array are achieved by using the reduced coupling wire inverted-V dipole design. Both antenna coupling and phased array analyses are performed using numerical simulation. Full-scale, in situ receive coupling measurements are performed to validate the simulation results. [ABSTRACT FROM AUTHOR]

A number of new and planned radio telescopes will consist of large arrays of low-gain antennas operating at frequencies below 300 MHz. In this frequency regime, Galactic noise can be a significant or dominant contribution to the total noise. This, combined with mutual coupling between antennas, makes it difficult to predict the sensitivity of these instruments. This paper describes a system model and procedure for estimating the system equivalent flux density (SEFD)-a useful and meaningful metric of the sensitivity of a radio telescope-that accounts for these issues. The method is applied to LWA-1, the first “station” of the Long Wavelength Array (LWA) interferometer. LWA-1 consists of 512 bowtie-type antennas within a 110 × 100 m elliptical footprint, and is designed to operate between 10 MHz and 88 MHz using receivers having noise temperature of about 250 K. It is shown that the correlation of Galactic noise between antennas significantly desensitizes the array for beam pointings which are not close to the zenith. It is also shown that considerable improvement is possible using beamforming coefficients which are designed to optimize signal-to-noise ratio under these conditions. Mutual coupling is found to play a significant role, but does not have a consistently positive or negative influence. In particular, we demonstrate that pattern multiplication (assuming the behavior of single antennas embedded in the array is the same as those same antennas by themselves) does not generate reliable estimates of SEFD. [ABSTRACT FROM AUTHOR]

In this paper, a rigorous procedure for calculating the antenna noise temperature is described, and applied to the antenna of BEST-i (Basic Element for SKA Training - version i), which represents one of the SKA (Square Kilometer Array) demonstrators. The SKA will be a new-generation radio telescope, with a collecting area 50 times larger than the area of today's largest radio telescope. BEST is the Italian reduced-scale SKA demonstrator, based on the re-instrumentation of about 8000 m² of the Northern Cross radio telescope, built with cylindrical parabolic antennas. In order to perform the antenna-temperature analysis, an electromagnetic tool to accurately evaluate the antenna pattern in the whole space surrounding the antenna itself is required. We used the commercial software GRASP8, developed by TICRA, to characterize reflector antennas. The antenna temperature was evaluated using the guideline adopted by the Antenna Task Force of the SKA world consortium. For BEST-1 at 408 MHz, we found an antenna temperature equal to 30 K in the zenith direction and 60 K at the horizon. The numerical results have been verified through several celestial calibration radio sources. [ABSTRACT FROM AUTHOR]

The eight-meter-wavelength transient array (ETA) is a new radio telescope consisting of 12 dual-polarized, 38 MHz-resonant dipole elements which are individually instrumented, digitized, and analyzed in an attempt to detect rare and as-yet undetected single dispersed pulses believed to be associated with certain types of astronomical explosions. This paper presents the design and demonstrated performance of ETA's dipole antennas. An inverted V-shaped design combined with a simple and inexpensive active balun yields sensitivity which is limited only by the external noise generated by the ubiquitous Galactic synchrotron emission over a range greater than the 27-49 MHz design range. The results confirm findings from a recent theoretical analysis, and the techniques described here may have applications in other problems requiring in situ evaluation of large low-frequency antennas. [ABSTRACT FROM AUTHOR]

In this paper, functional restrictions on the orientation of the onboard systems of the space radio telescope, stations of scientific data receiving and ground radio telescopes in the RadioAstron project are considered. Restrictions important for practical problems of scheduling observations with ground-space radio interferometer are discussed in detail. An algorithm for calculating the angles of the narrow-beam antenna drive, which takes into account technological restrictions on the capability of its spatial orientation, is presented. [ABSTRACT FROM AUTHOR]

A general approach to determination of geometrical parameters of planar array antennas designed for forming of orthogonal beams steered in the nodes of a Cartesian periodic lattice specified in the space of direction cosines is proposed. The proof of orthogonality of the complex amplitude distributions and appropriate array factors for the arrays constructed according to the proposed approach is given. The role of the array element patterns in providing the beam pattern orthogonality is underlined. The issue of the number of the array elements necessary for forming of the specified number of beams is discussed. A few demonstrative examples of the beam clusters and appropriate configurations of the arrays where the number of the elements is equal to the specified number of the beams are considered. [ABSTRACT FROM PUBLISHER]

Electrically small clear aperture dual offset reflector systems often exhibit a directivity ripple over frequency due to the interference of the diffracted field from the sub-reflector with the main beam field. This paper investigates the cause of the ripple, and presents a technique to predict the expected system directivity, including the ripple, using the feed radiation pattern augmented by an efficient simulation strategy in a clear aperture offset Gregorian system. The method allows for accurate prediction of the directivity ripple using a severely under-sampled set of simulation results. Predicted results are compared to several simulations, and agreement to better than 0.5 % is found for the majority of configurations using both analytical and full wave simulated feed patterns. [ABSTRACT FROM PUBLISHER]

This paper examines the performance of dual-linear sinuous antennas on silicon extended hemispherical silicon dielectric lenses. A theoretical impedance of 106 \Omega is identified based on the analysis of an ideal self-complementary structure, and this result compares well with simulations and measurements. The radiation properties of a linearly polarized sinuous antenna are simulated using Method of Moments software coupled to a GO/PO code, and also agree well with measurements. The results indicate that the sinuous antenna is an excellent wideband planar feed for a silicon lens, with cross-polarization levels below -17~\ dB, and polarization variations of \pm 5^\circ over two octaves in frequency. The application areas are millimeter-wave, wideband, dual-polarized radio-astronomy receivers. [ABSTRACT FROM PUBLISHER]

The system design of a cryogenic 2-13 GHz feed is considered with emphasis on its application in future wideband radio telescope systems. The feed is based on the so-called Eleven antenna and the design requires careful integration of various sub-designs in order to realize cryogenic operation. The various sub-designs include the electrical design of the Eleven antenna, design of the critical center puck, alternative solutions for integrating the Eleven antenna with low-noise amplifiers (LNAs), mechanical and cryogenic design and tests, and system noise temperature estimation and measurements. A great deal of simulated and measured results are presented throughout this paper, including the electrical, mechanical and cryogenic performance, and an assessment of the system noise temperature. The objective of this work is to present a good feed candidate that is well-suited for VLBI2010 and SKA radio telescopes. Further developments needed to completely fulfill the requirements for these future wideband radio telescopes are also discussed. [ABSTRACT FROM AUTHOR]

We present two methods for measuring the noise temperature of a differential input single-ended output low-noise amplifier (DISO LNA) connected to an antenna. The first method is the direct measurement of the DISO LNA and antenna in an anechoic chamber at ambient temperature. The second is a simple and low-cost noise parameter extraction of the DISO device using a coaxial long cable. The reconstruction of the DISO noise parameter from the noise wave measurements of the DISO LNA with one terminated input port is discussed in detail. We successfully applied these methods to the Murchison widefield array LNA and antenna. [ABSTRACT FROM AUTHOR]

The performance potential of the Cell/B.E., as well as its availability, have attracted a lot of attention from various high-performance computing (HPC) fields. While computation intensive kernels proved to be exceptionally well suited for running on the Cell, irregular data-intensive applications are usually considered as poor matches. In this paper, we present our complete solution for enabling such a data-intensive application to run efficiently on the Cell/B.E. processor. Specifically, we target radioastronomy data gridding and degridding, two resembling imaging filters based on convolutional resampling. Our solution is based on building a high-level application model, used to evaluate parallelization alternatives. Next, we choose the one with the best performance potential, and we gradually exploit this potential by applying platform-specific and application-specific optimizations. After several iterations, our target application shows a speed-up factor between 10 and 20 on a dual-Cell blade when compared with the original application running on a commodity machine. Given these results, and based on our empirical observations, we are able to pinpoint a set of ten guidelines for parallelizing similar applications on the Cell/B.E. Finally, we conclude the Cell/B.E. can provide high performance for data-intensive applications at the price of increased programming efforts and with a significant aid from aggressive application-specific optimizations. [ABSTRACT FROM AUTHOR]

Argus is an experimental antenna array system designed to demonstrate all-sky monitoring for transient signals in the frequency range 1200-1700 MHz. It currently consists of 22 broadband spiral antennas (expandable to 32) which are individually instrumented, digitized, and analyzed in an attempt to detect and localize both broadband and narrowband astronomical transients. In this paper, we describe the design of the instrument. Notable features include a novel array data aggregation architecture, a detection algorithm which does not require accurate calibration or detailed knowledge of the array manifold, and very low per-element cost of about US$lk/element. A sensitivity of at least 6.6 x 10-22 Wm-2 Hz-1 = 66 kJy (zenith at 1700 MHz for a 209 ms observation with 60 kHz bandwidth) is achieved for the system as implemented. Performance is demonstrated in an experiment in which the Sun is detected, localized, and tracked as it moves across the sky. Other experiments confirming the functionality of Argus as an all-sky surveillance system are summarized. [ABSTRACT FROM AUTHOR]

A field-trial system is presented in this paper to demonstrate that radio-over-fiber (RoF) techniques can be successfully applied to the remoting of a large antenna array for radio astronomical applications. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 48–54, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20898 [ABSTRACT FROM AUTHOR]

Interferometric image synthesis in radio astronomy is plagued by signal corruption from man-made sources. The very weak signals of interest can be overwhelmed by such interference. Recent work, has proposed using array signal processing techniques of adaptive beamforming, adaptive filtering, and subspace projection to remove interference prior to image synthesis. In some practical scenarios, we have found poor cancellation performance when using such methods. Because signal-of-interest levels in radio astronomy (RA) are usually well below the noise, even interference to noise ratios (INR) less than unity can affect signal estimation. At these low INRs, it is difficult to estimate interference parameters or statistics with sufficient accuracy for high-performance adaptive cancellation or subspace projection. By adding a few (one to three) low-gain (relative to the primary telescope dishes) "auxiliary" antennas to an array, it is possible to overcome this problem. This paper will show that using such antennas (e.g. commercial-grade 3-m dishes) with an existing array can significantly improve interference rejection. New extensions to subspace projection spatial filtering methods are presented, along with analytical and simulated results for performance comparison. [ABSTRACT FROM AUTHOR]

We built a Ka-band dual-circular-polarization low-noise receiver for the Misasa 54 m parabola antenna in Misasa, Japan. The antenna is designed to be combined with a transmitter and receiver system at the X band (around 8 GHz) and simultaneously with a receiver system at the Ka band. The Ka band is the frequency band around 30 GHz, which is important for deep-space communications and radio astronomy. The receiver comprises some waveguide components including a feed horn, a circular polarizer, and low-noise amplifiers. The components are installed in a vacuum vessel and are cooled to 4 K with a Gifford–McMahon refrigerator, providing low-noise performance. The receiver is capable of simultaneously handling the left- and right-hand circular-polarization (LHCP and RHCP) channels. The receiver-noise temperature was measured to be T RX ≃ 14 K in both the LHCP and RHCP channels. The system-noise temperature, including the antenna loss and atmospheric attenuation at the zenith, was measured to be T sys = 36–37 K in both the LHCP and RHCP channels on a clear day in September at Misasa. When the receiver is used with the X-band transmitter, the system-noise temperature is maintained at T sys ≃ 42 K in the RHCP channel. The degradation in the system-noise temperature is attributed to a frequency-selective reflector, which divides the signals in the X and Ka bands. There is no contamination from the transmitter to damage the receiver. The receiver has already been in use for deep-space communications and radio-astronomy observations. Our team in the radio-astronomy laboratory of ISAS/JAXA is responsible for the development of the receiver and the measurements of its performance. [ABSTRACT FROM AUTHOR]

The design of a low-loss, frequency-selective surface (FSS) for dual-frequency radioastronomical applications is discussed in this paper. The dichroic surface is inserted between the subreflectorand the receiver—which is located at the secondary focus of the radiotelescope—to split the main beam of the antenna into two, and direct them toward receivers operating at X- and K-bands, enabling simultaneous observation of arbitrarily polarized radio signals at these frequencies. Particular attention has been devoted to minimizing the overall attenuation introduced by the screen, which plays a critical role in determining the noise temperature of the radiotelescope. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 20: 126–129, 1999. [ABSTRACT FROM AUTHOR]

In this paper, a wideband high gain Vivaldi antenna based on spoof surface plasmon polaritons metamaterial for radio astronomy application is proposed. The height of the spoof surface plasmon polaritons structures fits the exponential function, thus the structure is named exponential spoof surface plasmon polaritons (ESSPP) metamaterial. With the exponential heights, the ESSPP metamaterial could correct the phase difference in a wide band, the gain is improved in the wide frequency range from 3 GHz to 9 GHz, and the proposed antenna exhibits stable radiation patterns with an average gain of 10.6 dBi. [ABSTRACT FROM AUTHOR]

Cube Satellite (CubeSat) technology is an attractive emerging alternative to conventional satellites in radio astronomy, earth observation, weather forecasting, space research, and communications. Its size, however, poses a more challenging restriction on the circuitry and components as they are expected to be closely spaced and very power efficient. One of the main components that will require careful design for CubeSats is their antennas, as they are needed to be lightweight, small in size, and compact or deployable for larger antennas. This paper presents a review of antennas suitable for picosatellite applications. An overview of the applications of picosatellites will first be explained, prior to a discussion on their antenna requirements. Material and antenna topologies which have been used will be subsequently discussed prior to the presentation of several deployable configurations. Finally, a perspective and future research work on CubeSat antennas will be discussed in the conclusion. [ABSTRACT FROM AUTHOR]

The next-generation Event Horizon Telescope (ngEHT) will be a significant enhancement of the Event Horizon Telescope (EHT) array, with ∼10 new antennas and instrumental upgrades of existing antennas. The increased u v -coverage, sensitivity, and frequency coverage allow a wide range of new science opportunities to be explored. The ngEHT Analysis Challenges have been launched to inform the development of the ngEHT array design, science objectives, and analysis pathways. For each challenge, synthetic EHT and ngEHT datasets are generated from theoretical source models and released to the challenge participants, who analyze the datasets using image reconstruction and other methods. The submitted analysis results are evaluated with quantitative metrics. In this work, we report on the first two ngEHT Analysis Challenges. These have focused on static and dynamical models of M87* and Sgr A* and shown that high-quality movies of the extended jet structure of M87* and near-horizon hourly timescale variability of Sgr A* can be reconstructed by the reference ngEHT array in realistic observing conditions using current analysis algorithms. We identify areas where there is still room for improvement of these algorithms and analysis strategies. Other science cases and arrays will be explored in future challenges. [ABSTRACT FROM AUTHOR]

We report a design solution for a highly reliable, low-noise and extremely efficient cryogenically cooled transmit/receive unit for a large antenna system meant for radio-astronomical observations and deep-space communications in the X band. We describe our design solution and the results of a series of laboratory and antenna tests carried out in order to investigate the properties of the cryogenically cooled low-noise amplifier developed. The transmit/receive unit designed for deep-space communications (Mars missions, radio observatories located at Lagrangian point L2, etc.) was used in practice for communication with live satellites including 'Radioastron' observatory, which moves in a highly elliptical orbit. [ABSTRACT FROM AUTHOR]

This paper presents the design of a compact front-end diplexer for radio-astronomy applications based on a self complementary Bow-tie antenna, a 3 dB T-junction splitter and two pass-band fractal filters. The whole diplexer structure has been optimized by using an evolutionary algorithm. In particular the problem of the diplexer design is recast into an optimization one by defining a suitable cost function which is then minimized by mean of an evolutionary algorithm namely the Particle Swarm Optimization (PSO). An X band diplexer prototype was fabricated and assessed demonstrating a good agreement between numerical and experimental results. [ABSTRACT FROM AUTHOR]

Antenna is one of the important subsystem components in a radio telescope system. In this paper, analysis on the effect of parasitic element on 408 MHz antenna in a radio telescope system is presented. Higher gain up to 10.24 dBi with reduction on beamwidth size has been achieved by optimizing the position of parasitic element relative to the driven element. The proposed antenna is suitable to be utilized in a transient radio telescope array. [ABSTRACT FROM AUTHOR]

Millimeter and sub-millimeter waves have been the focus of intensive research activities over the past several years. Application of these technologies has advanced beyond traditional high-cost niche uses - mostly related to radio astronomy and space applications - to embrace widespread new consumer applications, some of which show significant market potential. Increased opportunity to exploit these bands is in part created by the spectrum availability that enables extremely high data rates and the inherent miniaturizability of the radio front-ends. This naturally drives concomitant advancements in semiconductor technology at mm-waves and sub-millimeter waves that lower technology deployment cost and make it affordable for applications such as home multi-gigabit wireless systems, active and passive high resolution imaging for medical diagnostic or civil security applications, automotive radar, and body-area networks. [ABSTRACT FROM PUBLISHER]

Calibration of a sensor array is more involved if the antennas have direction dependent gains and multiple calibrator sources are simultaneously present. We study this case for a sensor array with arbitrary geometry but identical elements, i.e., elements with the same direction dependent gain pattern. A weighted alternating least squares (WALS) algorithm is derived that iteratively solves for the direction independent complex gains of the array elements, their noise powers and their gains in the direction of the calibrator sources. An extension of the problem is the case where the apparent calibrator source locations are unknown, e.g., due to refractive propagation paths. For this case, the WALS method is supplemented with weighted subspace fitting (WSF) direction finding techniques. Using Monte Carlo simulations we demonstrate that both methods are asymptotically statistically efficient and converge within two iterations even in cases of low SNR. [ABSTRACT FROM AUTHOR]

A novel design methodology is presented for correlator antenna arrays in radio astronomy applications. In order to characterize the spatial-filter-like performance of a correlator array, an analyzer is developed to calculate its u-v coverage and synthesized beam, along with the capability to simulate the Earth rotation effect and the image retrieval process. On the other hand, particle swarm optimization (PSO) is applied to determine the locations of antenna elements in typical open-ended and closed array configurations (such as the "Y" and the Reuleaux triangle), in order to achieve either the maximum u-v coverage or a synthesized beam with the lowest sidelobe level (SLL). Optimized arrays are observed to outperform uniform arrays and representative existing designs. [ABSTRACT FROM AUTHOR]

The latest generation of Cassegrain radio astronomy antennas is designed for multiple frequency bands with receivers for individual bands offset from the antenna axis. The offset feed arrangement typically has two focusing elements in the form of ellipsoidal mirrors in the optical path between the feed horn and the antenna focus. This arrangement aligns the beam from the offset feed horn to illuminate the subreflector. The additional focusing elements increase the number of design variables, namely the distances between the horn aperture and the first mirror and that between the two mirrors, and their focal lengths. There are a huge number of possible combinations of these four variables in which the optics system can take on. The design aim is to seek the combination that will give the optimum antenna efficiency, not only at the centre frequency of the particular band but also across its bandwidth. To pick the optimum combination of the variables, it requires working through, by computational mean, a continuum range of variable values at different frequencies which will fit the optics system within the allocated physical space. Physical optics (PO) is a common technique used in optics design. However, due to the repeated iteration of the huge number of computation involved, the use of PO is not feasible. We present a procedure based on using multimode Gaussian optics to pick the optimum design and using PO for final verification of the system performance. The best antenna efficiency is achieved when the beam illuminating the subreflector is truncated with the optimum edge taper. The optimization procedure uses the beam's edge taper at the subreflector as the iteration target. The band 6 receiver optics design for the Atacama Large Millimetre Array (ALMA) antenna is used to illustrate the optimization procedure. [ABSTRACT FROM AUTHOR]

The increasing demand of ultra-wide band (UWB) antennas in reflector systems, especially for radioastronomy, necessitates the analysis of reflector losses for directive UWB feeds. UWB technology has significant advantages; however its usage in reflector systems brings some extra losses to be considered. Ideally, all areas of the reflector should be illuminated with equal energy from the feed antenna at all frequencies of the band. However, this is not possible for a wide band system. Different phase center locations and 10 dB beamwidth values at different frequencies within the band result in spillover, amplitude taper and phase losses in a reflector system. These losses should be analyzed in detail for the effectively working of the system. The purpose of this work is to discuss the additional losses that occur in a UWB reflector system and demonstrate these losses with a given example. A directive Vivaldi antenna is used as the feed antenna of the UWB reflector and the effect of the losses on the directivity is shown. [ABSTRACT FROM AUTHOR]

The results of a large number of the antenna radiometric measurements at bands of 92, 18, 6.2, 1.35, and 1.7-1.2 cm are presented by the data of the standard telemetry system of the Spektr-R spacecraft. Both special sessions of calibration object observations in the mode of a single space radio telescope (SRT) operation and numerous observations of researched sources in the mode of the ground-space interferometer were used. The obtained results agree with the first results of Kardashev et al. (2013), i.e., within 10-15% at bands of 92, 18, and 6.2 cm and 20-25% at the band of 1.35 cm. In the main, the measurements for the eight subbands at wavelengths of 1.7-1.2 cm indicate a monotonic increase in the spectral system equivalent flux density (SEFD) of noise radiation with a frequency consistent with the calculated estimates for the discussed model. The sensitivity of the ground-space interferometer for the five subbands at wavelengths from 1.35 to 1.7 cm can be higher by a factor of 1.5, and for the three subbands from 1.35 to 1.2 cm lower by a factor of 1.5 than at the band of 1.35 cm. The SRT contribution to the interferometer sensitivity proportional to the square root of SEFD is close to the design one at the bands of 92 and 18 cm and decreases the design sensitivity approximately by a factor of 1.5 and 2 at the bands of 6.2 and 1.35 cm, respectively. These differences of implemented values from the design ones were not significantly affected the scientific program implementation. [ABSTRACT FROM AUTHOR]

A circular quadruple-ridged flared horn achieving almost-constant beamwidth over 6:1 bandwidth is presented. This horn is the first demonstration of a wideband feed for radio telescopes which is capable of accommodating different reflector antenna optics, maintains almost constant gain and has excellent match. Measurements of stand-alone horn performance reveal excellent return loss performance as well as stable radiation patterns over 6:1 frequency range. Physical optics calculations predict an average of 69% aperture efficiency and 13 K antenna noise temperature with the horn installed on a radio telescope. [ABSTRACT FROM PUBLISHER]

We describe the development of two circularly symmetric antennas with high polarization purity and low spill-over. Both were designed to be used in an all-sky polarization and intensity survey at 5 GHz (the C-Band All-Sky Survey, C-BASS). The survey requirements call for very low cross-polar signal levels and far-out sidelobes. Two different existing antennas, with 6.1-m and 7.6-m diameter primaries, were adapted by replacing the feed and secondary optics, resulting in identical beam performances of 0.73^\circ FWHM, cross-polarization better than -50 dB, and far-out sidelobes below -70 dB. The polarization purity was realized by using a symmetric low-loss dielectric foam support structure for the secondary mirror, avoiding the need for secondary support struts. Ground spill-over was largely reduced by using absorbing baffles around the primary and secondary mirrors, and by the use of a low-sidelobe profiled corrugated feedhorn. The 6.1-m antenna and receiver have been completed and tested. Results show that the co-polar beam matches the design simulations very closely in the main beam and down to levels of -80 dB in the backlobes. With the absorbing baffles in place the far-out (>100^\circ) sidelobe response is reduced below -90 dB. Cross-polar response could only be measured down to a noise floor of -20 dB but is also consistent with the design simulations. Temperature loading and groundspill due to the secondary support were measured at less than 1 K. [ABSTRACT FROM PUBLISHER]

At a 2007 Square Kilometre Array Design Studies (SKADS) workshop in Dwingeloo, Wim van Cappellen of the Nether lands Institute for Radio Astronomy (ASTRON) gave a presentation on figures of merit, in which he memorably compared antenna terms to apples. What seems like a simple, homogeneous fruit comes in all colors and varieties. Similarly, a survey of antenna literature and textbooks shows that authors use a wide variety of antenna figures of merit, often not in compliance with the relevant IEEE Standard Definitions of Terms for Antennas [1]. Since this standard is now in the process of revision by the Antennas and Propagation Society Antenna Standards Committee, it seems worth while to consider the standard, and clarify some common mis understandings and inconsistent usages. [ABSTRACT FROM AUTHOR]

An array of bow-tie slot antennas coupled through an extended hemispherical lens is proposed to operate in the 30 GHz frequency band. The design includes a combination of three microstrip Wilkinson power dividers (WPD) and transitions to coplanar wave guides (CPW) to form the feeding antenna network. This configuration is suitable for the integration with heterodyne imaging detectors commonly used in radioastronomy. Measurements and simulation results exhibit a frequency range of operation from 20 to 40 GHz with a bandwidth of 24% achieved for −10 dB return loss at the central frequency. The measured radiation patterns show a maximum peak gain of around 13 dB with HPBW of 10° for the E-plane, and whose first side lobes are lower than 13 dB below the main lobe in both angular shift sides. The presented results will be considered as preliminary feasibility studies in the 30 GHz QUIJOTE-CMB Instrument, which is designed to study the anisotropies of the Cosmic Microwave Background (CMB). [ABSTRACT FROM AUTHOR]

The pulse structure of the pulsar B1822-09 has been studied at 112, 62, and 42 MHz. The observations were conducted in 2010 on the Large Scanning Antenna and the DKR-1000 radio telescope of the Pushchino Radio Astronomy Observatory. The shape of the main pulse and interpulse undergo considerable changes at low radio frequencies. In the main pulse, the precursor disappears and is replaced by a new component that trails 50 ms behind the main component. At 62 MHz, the interpulse acquires a pronounced two-peaked shape. At 62 and 112 MHz, as well as at higher frequencies, the brighter second component of the interpulse follows the main pulse at 185° and has a relative amplitude of about 5%. The main pulse width changes with frequency according to the power law W ∼ ν in the frequency range 42-4750-MHz. The interpulse width follows this law only in the range 325-4750 MHz; at 112, 102, and 62 MHz, the interpulse is almost a factor of three broader than themain pulse. The parameters of the pulse's scattering on interstellar plasma inhomogeneities and the initial pulse width before it enters the scattering medium have been measured at 62 and 42 MHz. The frequency dependence of the characteristic scale for scattering of the pulses of B1822-09 corresponds to a Kolmogorov spectrum for the electron-density fluctuations in the interstellar medium in the direction toward this pulsar. [ABSTRACT FROM AUTHOR]

The proposed next-generation radio-telescope, the Square Kilometre Array (SKA), has ~3000 parabolic dish antennas and operates over many gigahertz of bandwidth. This results in a telescope with correlator requirements ~10 000 times more than any current telescope. This will be a challenge using traditional approaches. A method is proposed that will reduce the computational requirements for that part of the SKA where the antenna separation is not too great. This is done by deliberately introducing redundancy so that many of the outputs of the correlator measure the same data. We then show that the sum of these redundant correlations can be obtained efficiently by the use of fast convolution. The degree to which computational requirements are reduced is selectable. This translates directly into a power saving in the correlator and image processing. [ABSTRACT FROM AUTHOR]

An L-band low-noise phased array feed antenna was designed, fabricated, and characterized experimentally. The element design was optimized for an active impedance matching condition with a given set of nonuniform amplitude beamformer coefficients associated with a formed PAF beam. Using measured array S-parameters and modeled array element patterns, the predicted boresight beam equivalent system noise temperature and aperture efficiency at prime focus with uncooled low-noise amplifiers were 42 K and 61% at 1600 MHz. Experimental measurements of receiver noise using an array Y-factor technique matched modeled predictions. The array feed was mounted on the Arecibo radio telescope for on-reflector characterization. The measured boresight beam sensitivity figure of merit (Tsys/ηap) was 88 K and the 1 dB sensitivity bandwidth was 450 MHz. [ABSTRACT FROM AUTHOR]

We describe the design and construction of a dual-polarized phased-array feed (PAF) with the purpose of demonstrating this technology as a means of expanding the instantaneous field-of-view of radio telescopes. The PAF beamformer is calibrated with observations of an unpolarized astronomical radio source, the covariance matrix of all receiver channels is calculated, and the two dominant eigenvectors are then used as beamformer weights. We show measurements demonstrating the capabilities of this instrument as a polarimeter, and confirm that the calibration method does produce orthogonally-polarized beams. These results are then analyzed to show the sensitivity to fluctuations in gain and phase in the multiple parallel receiver chains making up the phased-array feed. We also compare the performance of PAFs that beamform all array elements with PAFs that beamform only co-polarized elements. [ABSTRACT FROM AUTHOR]

A set of techniques are presented that are based on the exploitation of low correlation sequences called Almost Difference Sets (ADSs) to design correlator arrays for radio astronomy applications. Three approaches are discussed with different objectives and performances. ADS-based analytical designs, GA -optimized arrangements, and PSO optimized arrays are presented and applied to the synthesis of open-ended "Y" and "Cross" array configurations to maximize the u - v coverage or to minimize the peak sidelobe level (PSL). Representative numerical results are illustrated to point out the features and performances of the proposed approaches, and to assess their effectiveness in comparison with state-of-the-art design methodologies, as well. The presented analysis indicates that the proposed approaches overcome existing PSO-based correlator arrays in terms of PSL control (e.g., >; 1.0 dB reduction) and tracking u - v coverage (e.g., up to 2% enhancement), also improving the speed of convergence of the synthesis process. [ABSTRACT FROM AUTHOR]

We present the design and development of the electronic multi-beam radio astronomy concept (EMBRACE), a demonstrator that is part of the European contribution towards the square kilometre array, which is currently being designed by the global radio astronomical community. One of the design goals of EMBRACE is to demonstrate the applicability of phased array technology for use in future radio telescopes. The EMBRACE system will ultimately consist of two stations, the largest of which comprises over 20,000 elements and has a physical area of about 160 m2 . The antenna system, covering the 500-1500 MHz frequency range, is designed as a dual polarized system, however only the signals for one polarization are processed. To obtain a cost effective design, RF analog beam-forming is performed on tile level close to the radiators. The demonstrator is designed to provide two independent beams such that different parts of the sky can be observed simultaneously. First results from part of the array are presented and discussed. The results show that the complete data path is functional. Since the design resembles a large regular contiguous array, all coupling can be taken into account in the embedded element patterns. The array factor therefore suffices to describe the scanning of the array reducing significantly calibration complexity compared to, e.g. sparse, random or more irregular arrays. This is confirmed by the first array factor measurements, that were done using a novel technique that does not require calibration of the array. The first measurements on an astronomical source, the Sun, indicate that the system noise temperature lies between 104 and 118 K, which is reassuringly close to the design target of 100 K. [ABSTRACT FROM AUTHOR]

A real-time spatio-temporal (ST) 3D FIR Frustum filter is proposed for improving the SNR of broadband focal plane array (FPA) signals. The 3D stop band of the proposed filter attenuates non-reflected off-dish signals, such as radio frequency interference (RFI), and also attenuates noise due to local thermal sources (e.g., ground) as well as receiver noise. The frustum-shaped 3D pass band transmits, with low distortion, desired broadband reflected celestial signals, as received by the focal plane array (FPA) of receiving elements. It is shown that, for pulsar-timing and pulsar-profile studies, the pre-processing of FPA signals using the proposed 3D ST Frustum filter-based beamforming method, prior to coherent de-dispersion, yields lower distortion than the 3D conjugate field matching (CFM) method (when appropriately extended from 2D to 3D) and also lower distortion than the conventional 2D spatial-only beamforming method. [ABSTRACT FROM AUTHOR]