J. G. Bij de Vaate

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.

Characterization of a Low-Frequency Radio Astronomy Prototype Array in Western Australia

We report characterization results for an engineering prototype of a next-generation low-frequency radio astronomy array. This prototype, which we refer to as the Aperture Array Verification System 0.5 (AAVS0.5), is a sparse pseudorandom array of 16 log-periodic antennas designed for 70-450 MHz. It is colocated with the Murchison widefield array (MWA) at the Murchison radioastronomy observatory (MRO) near the Australian square kilometre array (SKA) core site. We characterize the AAVS0.5 using two methods: in situ radio interferometry with astronomical sources and an engineering approach based on detailed full-wave simulation. In situ measurement of the small prototype array is challenging due to the dominance of the Galactic noise and the relatively weaker calibration sources easily accessible in the southern sky. The MWA, with its 128 “tiles” and up to 3 km baselines, enabled in situ measurement via radio interferometry. We present array sensitivity and beam pattern characterization results and compare to detailed full-wave simulation. We discuss areas where differences between the two methods exist and offer possibilities for improvement. Our work demonstrates the value of the dual astronomy-simulation approach in upcoming SKA design work.

The Phased Array Approach to SKA, Results of a Demonstrator Project

A phased-array demonstrator known as the Thousand Element Array (THEA) is currently under construction of which the first results are presented in this paper. THEA is an out-door phased array system that is able to detect signals from different strong astronomical sources simultaneously (multi-beaming). It consists of sixteen one square meter tiles (arrays) operating in the frequency band of 600-1700MHz. The beamforming for THEA is done at two levels; Radio Frequency (RF) beamforming on every tile (64 elements) and digital beamforming with the sixteen tiles, Smolders (1). First result will be presented in this paper.

Beamforming techniques for large-N aperture arrays

Beamforming is central to the processing function of all phased arrays and becomes particularly challenging with a large number of antenna element (e.g. >100,000). The ability to beamform efficiently with reasonable power requirements is discussed in this paper. Whilst the most appropriate beamforming technology will change over time due to semiconductor and processing developments, we present a hierarchical structure which is technology agnostic and describe both Radio-Frequency (RF) and digital hierarchical beamforming approaches. We present implementations of both RF and digital beamforming systems on two antenna array demonstrators, namely the Electronic Multi Beam Radio Astronomy ConcEpt (EMBRACE) and the dualpolarisation all-digital array (2-PAD). This paper will compare and contrast both digital and analogue implementations without considering the deep system design of these arrays.

Achieving Wideband sub-1dB Noise Figure and High Gain with MOSFETs if Input Power Matching is not Required

A 0.18 mum CMOS low noise amplifier (LNA) achieves sub-1 dB noise figure over more than an octave of bandwidth without external noise matching components. It is designed for a future radio telescope, requiring millions of cheap LNAs mounted directly on phased array antenna elements. The short distance between antenna and LNA and low frequency below 2 GHz allows for using an LNA with reflective input impedance, increasing the gain with 6 dB. Without any matching network, very low noise figure is achieved over a wide bandwidth. At 90 mW power, sub-1 dB Noise is achieved for 50 Omega source impedance over a 0.8-1.8 GHz band without external coils, and S21>20 dB, OIP2>25 dBm and OIP3>15 dBm. Preliminary results with 150 Omega source impedance show noise temperatures as low as 25 K around 900 MHz.

Electronic Multi-Beam Radio Astronomy Concept: Embrace a Demonstrator for the European SKA Program

ASTRON has demonstrated the capabilities of a 4m2, dense phased array antenna (Bij de Vaate et al., 2002) for radio astronomy, as part of the Thousand Element Array project (ThEA). Although it proved the principle, a definitive answer related to the viability of the dense phased array approach for the SKA could not be given, due to the limited collecting area of the array considered. A larger demonstrator has therefore been defined, known as “Electronic Multi-Beam Radio Astronomy Concept“, EMBRACE, which will have an area of 625 m2, operate in the band 0.4–1.550 GHz and have at least two independent and steerable beams.With this collecting area EMBRACE can function as a radio astronomy instrument whose sensitivity is comparable to that of a 25-m diameter dish. The collecting area also represents a significant percentage area (∼10%) of an individual SKA “station.” This paper presents the plans for the realisation of the EMBRACE demonstrator.

Mid-frequency aperture arrays: the future of radio astronomy

Aperture array (AA) technology is at the forefront of new developments and discoveries in radio astronomy. Currently LOFAR is successfully demonstrating the capabilities of dense and sparse AAs at low frequencies. For the mid-frequencies, from 450 to 1450MHz, AAs still have to prove their scientific value with respect to the existing dish technology. Their large field-of-view and high flexibility puts them in an excellent position to do so. The Aperture Array Verification Program is dedicated to demonstrate the feasibility of AAs for science in general and SKA in particular. For the mid-frequency range this has lead to the development of EMBRACE, which has already demonstrated the enormous flexibility of AA systems by observing HI and a pulsar simultaneously. It also serves as a testbed to demonstrate the technological reliability and stability of AAs. The next step will put AA technology at a level where it can be used for cutting-edge science. In this paper we discuss the developments to move AA technology from an engineering activity to a fully science capable instrument. We present current results from EMBRACE, ongoing tests of the system, and plans for EMMA, the next step in mid-frequency AA technology.

SKA Mid Frequency Aperture arrays: Technology for the ultimate survey machine

Higher frequency Aperture Array technology, up to 1.5GHz, is being prepared for large scale deployment in radio astronomy. Novel approaches in order to increase performance and lower the production costs are a key element of the success as well as scientific demonstration. This paper describes the current status, technology innovations and planned demonstrators.

Design of a Focal Plane Array system at cryogenic temperatures

This paper describes the system design and realization of a cryogenically cooled Focal Plane Array (FPA) for radio astronomy application. The system will consist of an antenna array, low noise amplifiers (LNA) and an RF beam former which are placed inside a cryostat. The antenna and the primary LNAs are cooled to 20 K, while the beam former will be at 77 K. The system design and the performance of the overall design are addressed.

Antenna array characterization via radio interferometry observation of astronomical sources

We present an in-situ antenna characterization method and results for a “low-frequency” radio astronomy engineering prototype array, characterized over the 75-300 MHz frequency range. The presence of multiple cosmic radio sources, particularly the dominant Galactic noise, makes in-situ characterization at these frequencies challenging; however, it will be shown that high quality measurement is possible via radio interferometry techniques. This method is well-known in the radio astronomy community but seems less so in antenna measurement and wireless communications communities, although the measurement challenges involving multiple undesired sources in the antenna field-of-view bear some similarities. We discuss this approach and our results with the expectation that this principle may find greater application in related fields.