Analysis of sky contributions to system temperature for low frequency SKA aperture array geometries

The new generation of radio telescopes, such as the proposed Square Kilometer Array (SKA) and the Low-Frequency Array (LOFAR) rely heavily on the use of very large phased aperture arrays operating over wide band-widths at frequency ranges up to approximately 1.4 GHz. The SKA in particular will include aperture arrays consisting of many thousands of elements per station providing un-paralleled survey speeds. Currently two different arrays (from nominally 70 MHz to 450 MHz and from 400 MHz to 1.4 GHz) are being studied for inclusion within the overall SKA configuration. In this paper we aim to analyze the array contribution to system temperature for a number of regular and irregular planar antenna array configurations which are possible geometries for the low-frequency SKA (sparse disconnected arrays). We focus on the sub-500 MHz band where the real sky contribution to system temperature (Tsys) is highly significant and dominants the overall system noise temperature. We compute the sky noise contribution to Tsys by simulating the far field response of a number of SKA stations and then convolve that with the sky brightness temperature distribution from the Haslam 408 MHz survey which is then scaled to observations at 100 MHz. Our analysis of array temperature is carried out by assuming observations of three cold regions above and below the Galactic plane. The results show the advantages of regular arrays when sampled at the Nyquist rate as well as their disadvantages in the form of grating lobes when under-sampled in comparison to non-regular arrays.

[1]  Cmb multipole measurements in the presence of foregrounds , 2006, astro-ph/0603369.

[2]  Larry A. Coldren,et al.  Wiley Series in Microwave and Optical Engineering , 2012 .

[3]  Jaap D. Bregman.  Concept design for a low-frequency array , 2000, Astronomical Telescopes and Instrumentation.

[4]  Alle-Jan van der Veen,et al.  Calibration challenges for future radio telescopes , 2010, IEEE Signal Processing Magazine.

[5]  R. Hansen.  Phased Array Antennas , 2009 .

[6]  T. Taylor.  Design of line-source antennas for narrow beamwidth and low side lobes , 1955 .

[7]  C.L. Dolph,et al.  A Current Distribution for Broadside Arrays Which Optimizes the Relationship between Beam Width and Side-Lobe Level , 1946, Proceedings of the IRE.

[8]  A. Rogers,et al.  SPECTRAL INDEX OF THE DIFFUSE RADIO BACKGROUND MEASURED FROM 100 TO 200 MHz , 2008, 0806.2868.

[9]  Peter N. Wilkinson,et al.  ELECTRONIC MULTI-BEAM RADIO ASTRONOMY CONCEPT: EMBRACE A DEMONSTRATOR FOR THE EUROPEAN SKA PROGRAM , 2004 .

[10]  Wim van Cappellen,et al.  Aperture Arrays for the SKA: Dense or Sparse? , 2006, astro-ph/0611160.

[11]  E. de Lera Acedo,et al.  Ultra-Wideband Aperture Array Element Design for Low Frequency Radio Astronomy , 2011, IEEE Transactions on Antennas and Propagation.

[12]  A.B. Smolders,et al.  THousand Element Array (THEA) , 2000, IEEE Antennas and Propagation Society International Symposium. Transmitting Waves of Progress to the Next Millennium. 2000 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (C.

[13]  Alan E. E. Rogers,et al.  The Murchison Widefield Array: Design Overview , 2009, Proceedings of the IEEE.

[14]  A. Hewish,et al.  Observation of a Rapidly Pulsating Radio Source , 1968, Nature.

[15]  C. G. T. Haslam,et al.  A 408 MHz all-sky continuum survey. I - Observations at southern declinations and for the North Polar region , 1981 .

[16]  A. Fenn.  Adaptive Antennas and Phased Arrays for Radar and Communications , 2007 .

[17]  Simon T. Garrington,et al.  SKADS Benchmark Scenario Design and Costing - 2 , 2008 .

[18]  Alan V. Oppenheim,et al.  Discrete-Time Signal Pro-cessing , 1989 .

[19]  Constantine A. Balanis,et al.  Antenna Theory: Analysis and Design , 1982 .

[20]  Robert J. Mailloux,et al.  Phased Array Antenna Handbook , 1993 .

[21]  P. Reich,et al.  A radio continuum survey of the southern sky at 1420 MHz - The atlas of contour maps , 2001 .

[22]  T. Tayor,et al.  Design of line-source antenna for narrow beamwidth and low sidelobes , 1955 .

[23]  W. Reich,et al.  A radio continuum survey of the northern sky at 1420 MHz. II , 1986 .

[24]  Nicholas Fourikis,et al.  Phased array-based systems and applications , 1997 .

[25]  F. Abdalla,et al.  Forecasts for dark energy measurements with future H i surveys , 2009, 0905.4311.

[26]  S. Ellingson,et al.  Antennas for the next generation of low-frequency radio telescopes , 2005, IEEE Transactions on Antennas and Propagation.

[27]  Max Tegmark,et al.  A model of diffuse Galactic radio emission from 10 MHz to 100 GHz , 2008, 0802.1525.

[28]  George D. Nicolson,et al.  The Rhodes/HartRAO 2326‐MHz radio continuum survey , 1998 .

[29]  S. Ellingson.  Sensitivity of Antenna Arrays for Long-Wavelength Radio Astronomy , 2010, IEEE Transactions on Antennas and Propagation.