A fast and accurate scheme for calibration of active phased-array antennas

The international radio-astronomy community is currently making detailed plans for the development of a new radio telescope: the Square Kilometre Array (SKA). This instrument will be a hundred times more sensitive than telescopes currently in use. One approach for this new telescope is to use a phased array consisting of more than 10/sup 6/ receiving elements with a mixed RF/digital adaptive beamformer. At this moment, a demonstrator receive-only active phased-array system is being tested at NFRA, the One Square Metre Array (OSMA). This is a scale model with 144 receiving elements with a mixed RF/digital beamforming architecture. One of the main issues in getting a high-performance phased-array system with accurate beam control and low side-lobes is an accurate and fast on-line calibration facility. The proposed "multi-element phase-toggle" (MEP) method is an extension of the phase-toggle method used by Lee, Chu and Lin (1993) and allows groups of elements to be calibrated simultaneously by using FFT signal processing techniques. Measured results from the OSMA system performance and of the remaining errors after MEP calibration are presented.