Beamforming for radio astronomy

[摘要] ENGLISH ABSTRACT: Beamforming is a technique used to combine signals from an array of antennas to effectivelysynthesize a single aperture and beam. In the Radio Astronomy community thetechnique is used to obtain a desirable beam pattern as well as to electronically point thebeam of an array. Next generation radio telescopes such as the Square Kilometre Array(SKA) surpass current technology and will extensively make use of beamforming techniques.Various factors determine the output of a beamformer; however, given an array with afixed configuration only the weights applied to the incoming signals affect the synthesizedaperture and beam. Furthermore, the incoming data must be processed in real-time, at arate equal to the input-output rate of the processor. Both the weighting function and thereal-time implementation of beamforming, are the primary subjects of this thesis.In this thesis various deterministic weighting functions are investigated. The algorithmsare implemented in a matlab program, serving as a simulation tool for investigating thetechniques. The program is verified by comparing the expected theoretical outcomes tothe simulated output. For the program the following functionalities are included: a steeringtechnique, spectral weighting, Dolph-Chebychev, and the Least Square Error algorithm. Applicationsof these techniques is investigated and their prominence in the Radio Astronomycommunity is established.For the real-time beamformer implementation, the UniBoard platform configured withbeamformer firmware, is investigated. This is important as the UniBoard is an excellentexample of a beamformer implementation within the Radio Astronomy community. Thearchitecture is used to emulate a linear array by implementing a python control script,where the output corresponded accurately with the expected theoretical values.The thesis also constitutes the design and implementation of a digital frequency domainbeamformer on the ROACH board. This processing board is employed by the Karoo ArrayTelescope (KAT-7) in South Africa. This work is therefore important as it demonstrates abeamformer implementation on an architecture in use by the Radio Astronomy community.An antenna array is designed and built for the verification of the beamformer design. Resultswith a good degree of accuracy were obtained and where errors exist they are discussed.

[发布机构] Stellenbosch University