Beamformer Design Methods for Radio Astronomical Phased Array Feeds

Abstract

A major emphasis in current radio astronomy instrumentation research is the use of phased array feeds (PAF) to provide radio telescopes with larger fields of view. One of the challenges of PAF systems is the design of beamformers that provide sufficient sensitivity and known, stable beam pattern structure. High sensitivity has been achieved with the maximum sensitivity beamformer without regard to beam pattern shape. Deterministic beamformers provide the desired pattern shape control, but suffer from a significant reduction in sensitivity. We present a hybrid beamforming method, which balances the tradeoff between high sensitivity and precise beam pattern shape control. A comparison of each of these beamforming methods, using measured data, confirms the advantage of the hybrid approach. The pattern distortions introduced by modeled beamformers can be mitigated with a transformation step, but ultimately it is shown that PAF beamformer design is best done using measured calibrators. A PAF calibration vector quality metric based on minimum description length is also introduced.Index Terms-Antenna array feeds, array signal processing, phased arrays, radio astronomy.

Antennas and Arrays

“…Multiple beams for a large parabolic antenna can greatly increase sky coverage, which is particularly useful for survey observations. A beamformer feed system in which beams are formed using phased arrays of feed elements is described by Elmer et al (2012), who consider various designs (see discussion in Sect. 5.7.2.1).…”

Antennas in Radio Telescope Systems

“…Processing of the array elements is typically done in the digital domain, introducing the possibility of optimizing the main lobe or sidelobes (perhaps even dynamically) and performing interference mitigation by nullforming; see, e.g., Landon et al (2010). Experimental phased array feeds have been demonstrated on small axisymmetric prime-fed systems (see in particular Elmer et al 2012) and on Arecibo (Warnick et al 2011) and will soon become the primary (permanent) feed systems for the WSRT and ASKAP (section "Other Prominent Interferometer-Type Radio Telescopes").…”

Multidimensional-DSP Beamformers Using the ROACH-2 FPGA Platform

“…Applications of antenna array-based electronically steerable directional beamformers can be found in a range of areas such as mobile communications, radar [1,2], microwave sensing, long-range detection and target tracking, cognitive radio and radio telescope arrays [3][4][5]. Ultra-wideband (UWB) beamforming on a uniform linear array (ULA) of broadband antennas [6,7] enables directional-selective enhancement of propagating far-field uniform plane wave signals having a given direction of arrival (DOA).…”