Beamforming and evaluation of focal plane arrays for radio astronomy
thesisposted on 2022-03-28, 19:22 authored by Douglas Brian Hayman
Dense focal plane arrays (FPAs) are a key technology for a new generation of radiotelescopes. Their primary benefit is the rapid survey speed facilitated by the wide field-of-view provided by multiple beams. Recent advances have brought dense FPAs within reach of radio astronomy applications and a number of institutions have significant research programs in this field. The size of the FPA required for a specified field-of-view is an important parameter for preliminary system design. In this thesis, this is examined by calculating the encircled power in the focal plane using physical optics. Design data is provided relating the FPA size, dish size, focal length and field-of-view for prime focus reflectors. A broad minimum in the FPA size for a dish focal length and diameter ratio (F/D) of 0.4 is found and over practical geometries, the FPA size is dependent on only F/D and the scan angle times dish diameter divided by wavelength. The utility of this design data is confirmed by comparing it with current FPA system designs. In an operational radiotelescope, factors such as electronic gain drift and imperfect modelling result in the beamformer weights being best determined adaptively. Therefore a 'black-box' approach is used in this work. The theoretical basis for this approach is detailed; the determination of the gain (G) and system temperature (T) and the calculation of the maximum sensitivity (G/T) weighting are shown. A prototype interferometer-radiotelescope, built at CSIRO's Radiophysics Laboratory in Sydney, is used to demonstrate a suite of techniques for FPA beamforming and evaluation for this thesis. The method for calculating the maximum G/T weighting is demonstrated by applying the blackbox model to parameters that are readily extracted from an appropriately equipped radiotelescope.