Abstract Details

Name: Bela Dixit
Affiliation: Giant Metrewave Radio Telescope, NCRA-TIFR
Conference ID: ASI2021_596
Title : L-band Aperture Array Beamformer: Prototype Implementation and Testing
Authors and Co-Authors : Bela S. Dixit(GMRT, NCRA-TIFR), Kaushal D. Buch(GMRT, NCRA-TIFR), Ajithkumar B.(GMRT, NCRA-TIFR), Atul Ghalame(GMRT, NCRA-TIFR), Jayaram N. Chengalur(NCRA-TIFR)
Abstract Type : Oral
Abstract Category : Instrumentation and Techniques
Abstract : The Expanded GMRT (eGMRT) is a proposal to investigate three possible expansions to the Giant Metrewave Radio Telescope (GMRT) - increasing the field-of-view (FoV) using the Focal Plane Array (FPA), the angular resolution and the sensitivity to extended radio emission. This paper discusses the development of an aperture array beamformer as a step towards FPA beamforming. The aim is to develop a multi-element, multi-beam prototype beamformer and perform an integrated testing with the 144-element (Vivaldi dipole elements) ASTRON L-band FPA. Through architectural optimization and use of FPGA re-configurability, we have implemented a 32 MHz bandwidth, 32-input, 5-beam beamformer on a single Virtex-5 FPGA. While in operation, initially, a 32-input correlator design which provides a full correlation matrix is programmed. The correlator output is processed offline for deriving weights for optimal beamforming. The FPGA is then re-programmed with appropriate weights to function as a real-time beamformer. The FPGA design can also packetize ADC voltages from the FPA elements and send these over the 10 Gigabit Ethernet for offline correlation and beamforming. The verification of aperture array beamformer is performed using experimental measurements in the free-space test range located at the GMRT site. This test range consists of a narrow-beam transmitting antenna and the aperture array as the receiving element. The aperture beam was steered across the beam of the transmitting antenna for broadband noise radiation (1.1 - 1.7 GHz). We have developed tests to form beams at boresight using the maxSNR technique which accounts for the coupling between the elements. A comparative analysis of the signal-to-noise ratio (SNR) improvement for the phased-array beamforming (ignoring mutual coupling between the elements) and the maxSNR techniques was carried out. This paper shall describe the above-mentioned aspects in detail along with ongoing efforts towards implementation of a wideband (300 MHz) beamformer and spectrometer on Xilinx RFSoC (RF System-on-Chip).