L. Bakker

APERTIF: Phased array feeds for the westerbork synthesis radio telescope

Present day synthesis radio telescopes have limited survey capabilities because of field of view restrictions. A novel method to form multiple beams on the sky is to employ a phased array feed (PAF). In telescopes with small f/D ratios, it is the only way to form closely packed beams on the sky. An additional advantage of this technique is that a PAF allows optimizing the secondary beam in terms of sensitivity, sidelobes and polarization characteristics. APERTIF (“APERture Tile In Focus”) is a PAF system that is being developed for the Westerbork Synthesis Radio Telescope (WSRT) to increase its survey speed with a factor 20. This paper presents a system overview of APERTIF and measurement results that demonstrate the unique capabilities of PAFs in practice: Wide field of view (scan range), low system temperature, excellent illumination efficiency, synthesis imaging and a significant reduction of the reflector — feed interaction.

Apertif, a focal plane array for the WSRT

In this paper we describe a focal plane array (FPA) prototype, based on Vivaldi elements, developed for the Westerbork Synthesis Radio Telescope (WSRT) to increase its instantaneous field of view by a factor 25 and double its current bandwidth. This prototype is the first step in a project that has the ambition to equip most of the WSRT antennas with FPAs to improve the survey speed of the telescope. Examples of scientific applications are surveys of the northern sky in polarised continuum and HI emission, and efficient searches for pulsars and transients.

Low cost low noise phased-array feeding systems for SKA pathfinders

Developments in radio astronomy instrumentation drive the need for lower cost front-ends due to the large number of antennas and low noise amplifiers needed. This paper describes cost reduction techniques for the realization of antennas and low noise amplifiers in combination with a noise budget calculation for array systems in the absence of cryogenic cooling.

Off-axis beam performance of Focal Plane Arrays for the Westerbork Synthesis Radio Telescope - Initial results of a prototype system

This paper reports on the off-axis beam performance of reflector antennas fed by Focal Plane Arrays (FPAs). The FPAs are comprised of many electrically small (≪ 0.5λ) elements that can be used to generate multiple closely overlapping beams on the sky. As a result, both the size and continuity of the telescopes Field Of View (FOV) can be substantially improved with respect to conventional reflector systems fed by single-horn or cluster feeds in a one-horn-per-beam configuration. The size of the FOV, in combination with the system sensitivity and instantaneous bandwidth, constitutes an important figure of merit, that is, FOV × BandWidth × Sensitivity2, and is proportional to the survey speed of a telescope which should be maximized. One example of such a design, based on this new technology, is APERTIF [1], which aims at increasing the survey speed of the Westerbork Synthesis Radio Telescope (WSRT) with a factor of ∼20.

Experimental results of a 112 element phased array feed for the Westerbork Synthesis Radio Telescope

This paper presented the progress in the characterization of a prototype PAF system: overlapping compound beams, sensitivity over the field of view, single dish imaging and fringes between the PAF system and multiple horn fed dishes. The development and characterization of phased array feeds is an ongoing effort. The results presented in this paper are an important step in demonstrating the feasibility and competitiveness of the PAF for radio astronomy.

Experimental Results for the Sensitivity of a Low Noise Aperture Array Tile for the SKA

Aperture arrays have been studied extensively for application in the next generation of large radio telescopes for astronomy, requiring extremely low noise performance. Prototype array systems need to demonstrate the low noise potential of aperture array technology. This paper presents noise measurements for an Aperture Array tile of 144 dual-polarized tapered slot antenna (TSA) elements, originally built and characterized for use as a Phased Array Feed for application in an L-band radio astronomical receiving system. The system noise budget is given and the dependency of the measured noise temperatures on the beam steering is discussed. A comparison is made of the measurement results with simulations of the noise behavior using a system noise model. This model includes the effect of receiver noise coupling, resulting from a changing active reflection coefficient and array noise contribution as a function of beam steering. Measurement results clearly demonstrate the validity of the model and thus the concept of active reflection coefficient for the calculation of effective system noise temperatures. The presented array noise temperatures, with a best measured value of 45 K, are state-of-the-art for room temperature aperture arrays in the 1 GHz range and illustrate their low noise potential.

Apertif - the focal-plane array system for the WSRT

We describe a focal plane array (FPA) system, called Apertif, that is being developed for the Westerbork Synthesis Radio Telescope (WSRT). The aim of Apertif is to increase the instantaneous field of view of the WSRT by a factor of 37 and its observing bandwidth to 300 MHz with high spectral resolution. This system will turn the WSRT into an effective survey telescope with scientific applications such as deep imaging surveys of the northern sky of HI and OH emission, of the polarised continuum and efficient searches for pulsars and transients. Such surveys will detect the HI in more than 100,000 galaxies out to z = 0.4, will allow to determine the detailed structure of the magnetic field of the Galaxy, and will discover more than 1,000 pulsars. We present experimental results obtained with a prototype FPA installed in one of the WSRT dishes. These results demonstrate that FPAs do have the performance that is required to make all these surveys possible.

Experimental results of the APERTIF phased array feed

APERTIF (APERture Tile In Focus) is a Phased Array Feed (PAF) system that is being developed for the Westerbork Synthesis Radio Telescope (WSRT) to increase its survey speed with a factor 20. This paper presents an overview of APERTIF and measurement results that demonstrate the unique capabilities of PAFs in practice: Wide field of view (scan range), low system temperature, excellent illumination efficiency, synthesis imaging and a significant reduction of the reflector feed interaction.

THE EVOLUTION OF GALAXIES THROUGH THE NEUTRAL HYDROGEN WINDOW

How large disk galaxies have evolved in, and out of, the blue cloud of actively star-forming galaxies as a function of environment and time is an outstanding question. Some of the largest disks become systems like M31, M33 and the Milky Way today. In denser environments, it appears they transform onto the red sequence. Tracking disk systems since z<0.5 as a function H I mass, dynamical mass, and environment should be possible in the coming decade. H I and optical data combined can sample outer and inner disk dynamics to connect halo properties with regions of most intense star-formation, and the gas reservoir to the co nsumption rate. We describe existing and future IFUs on 4-10m telescopes that complement upcoming H I surveys for studying disks at z<0.5. Multiple units, deployable over large fields-of-vie w, and with logarithmic sampling will yield kinematic and star-formation maps and properties of the stellar populations, resolving the core but retaining sensitivity to disk outskirts.