Nima Razavi-Ghods

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One of the biggest challenges in radio astronomy for the 21st century is the SKA telescope, the newest radio telescope in the world to be built as a Square Kilometre Array of antennas distributed in hundreds of stations to form an interferometric image of the sky. Below 1 GHz, these stations will be composed of thousands of inexpensive elements in a dense(More)
This paper shows how an accurate, compact and fast representation of the embedded element patterns can be provided by the combination of spherical waves. Examples will be given for wideband non-regular arrays of bow-tie antennas containing up to 1000 elements, at the level of embedded-element and array patterns. It is expected that the provided(More)
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The electromagnetic modeling and testing is presented for antenna elements devoted to the low frequency band of the Square Kilometre Array (SKA) telescope [1]. Covering a band from 70 to 450 MHz, these elements consist on a log-periodic dipole array (LPDA) model and they have been designed for maximum sensitivity across the band in the region +/- 45 degrees(More)
In this paper, the frequency domain (FD) SAGE (Space-Alternating Generalized Expectation-maximization) algorithm has been extended to the MIMO case in order to determine the angular and temporal channel characteristics at both ends of the radio link. The implementation of the SAGE algorithm relies on the serial interference cancellation (SIC) technique(More)
The paper discusses the architecture of MIMO channel sounders. The semi-sequential design is contrasted with the sequential and the parallel architectures. Measurements with an eight parallel receiver semi-sequential sounder performed in both indoor and outdoor environments at 2 GHz using different antenna arrays will be presented. The parallel receiver(More)
This paper provides an overview of the Aperture Array Verification System 0.5 (AAVS 0.5), co-located and operated in conjunction with the Murchison Widefield Array (MWA) near the Australian SKA core site. AAVS 0.5 is based on log-periodic antennas of a type potentially useful in next-generation low-frequency arrays such as SKA-low. We report on our progress(More)
Amplitude tapering can be employed for phased array systems in order to reduce the level of coherent sidelobes in a Nyquist sampled array. Whilst this is true for both regular and irregular geometries, the latter, which may be implemented for under-sampled regimes to avoid grating lobes, can benefit by a method of occupied area adjustment, in which the(More)
Correlation between SKA-LOW stations is studied in this paper. The mutual coupling is taken into account via embedded element patterns obtained from the simulation of the whole stations. To reduce the sidelobes in the correlated pattern, a rotation of stations is implemented. This results in a smoother behavior in the sidelobe region. Moreover, the(More)
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;(More)