Agaram Raghunathan

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We present the design, construction, and measurements of the electromagnetic performance of a wideband space beam splitter. The beam splitter is a sheet in free space that is designed to divide incident radiation into reflected and transmitted components for interferometer measurement of spectral features in the mean cosmic radio background. Analysis of a(More)
Precision measurements of the spectrum of the cosmic radio background require frequency independent antennas of small electrical dimensions. We describe the design of a wide-band fat-dipole antenna with a sinusoidal profile having a frequency independent performance over the octave band 87.5 to 175 MHz. The input return loss exceeds 15 dB and the radiation(More)
We have developed an interferometer method for measurement of broad-band spectrum of the low radio frequency celestial radiation background, which is of importance in understanding the Epoch of Reionization, when the first stars and galaxies formed in the evolving universe. We have used two antennas in a short-spacing east-west interferometer mode, with a(More)
The absolute temperature of the cosmic microwave background (CMB) has been measured at a frequency of 1280 MHz. The observation was made with a modified version of the L-band receiver used in the Giant Metre wavelength Radio Telescope (GMRT): the feed horn was replaced by a corrugated plate and the receiver was placed on the ground, directed at zenith, and(More)
Precision cosmology has been made possible by differential microwave radiometers that have imaged the anisotropy in the cosmic microwave background radiation. Continued progress is expected from measurement of spectral distortions in this cosmic radiation. A key distortion in the global sky spectrum is in the 40-250 MHz band and expected from variations in(More)
In this presentation I will give a brief overview of the on-going activities at Raman Research Institute (RRI). The present focus at RRI is on aperture arrays for low frequency radio astronomy. Appreciating the fact that SKA design will use the aperture array technology up to 1.4GHz, RRI has initiated design studies related to aperture phase array(More)
The challenging goal of detecting faint and wideband spectral features arising from cosmological evolution in the thermal state of the baryons has driven recent progress in radiometer technology. Because these faint signals are received with foregrounds and terrestrial RFI that are overwhelmingly larger in power, the design of sensors of the EM field and(More)
The cosmological evolution of baryons through recombination and reionization are predicted to manifest as faint spectral features in the cosmic radio background. Pathfinder experiments that aim to detect global phase transitions in the ionization state of the gas in redshifted 21-cm may well be the first radio wavelength constraints on the astrophysics that(More)
Detection of distortions in the spectrum of cosmic microwave background radiation (CMBR) is the current challenging problem in the modern observational cosmology. It holds key to understand the evolution of early universe. These distortions are predicted to be 8-9 orders of magnitude weaker than CMBR temperature and hence require an antenna with smoothly(More)
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