A study on data correlation for interferometric observations like vlbi and delta-dor applications and the correlation analysis of XF correlator

Abstract

Radio interferometric techniques have been applied to the tracking of spacecraft and enables precise measurement of the angular positions of spacecraft, stars and other cosmic objects in deep space. The image, or intensity distribution, of a source from the deep space has a Fourier transform that is the two-point correlation function of the electric field, whose components can be directly measured by an interferometer. In Very Long Baseline Interferometry (VLBI), the received signals are converted to an intermediate frequency low enough that they could be recorded directly on a magnetic tape and then given to the correlator. Delta differential One-way Ranging (ΔDOR), is an application of VLBI and is a powerful interplanetary navigation technique providing a direct measurement of the angular position of a spacecraft. The correlation processing is the core section of the receiving system and it gathers signals from independent antennas which are then processed to find essential data that are used for the guidance and navigation of a spacecraft. This paper explains the importance of data correlation in radio interferometry and then discusses different types of the correlators used for radio interferometry like XF, FX, HXF correlators. Then XF correlator will be explained in detail and the performance of time lag correlation section and the spectral response for different values of integration lengths of different time delays will be analysed.