A 6–12 GHz analogue lag-correlator for radio interferometry

¹ Cavendish Laboratory, Cambridge University, Cambridge CB3 0HE, UK e-mail: tk229@mrao.cam.ac.uk
² Ludwigshohenweg 11, 83253 Rimsting, Germany e-mail: holler@cantab.net
³ Sub.-Dept. of Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 7RH, UK

Received: 5 December 2006
Accepted: 22 December 2006

Abstract

Aims.We describe a 6–12 GHz analogue correlator that has been developed for use in radio interferometers.

Methods.We use a lag-correlator technique to synthesis eight complex spectral channels. Two schemes were considered for sampling the cross-correlation function, using either real or complex correlations, and we developed prototypes for both of them. We opted for the “add and square” detection scheme using Schottky diodes over the more commonly used active multipliers because the stability of the device is less critical.

Results.We encountered an unexpected problem, in that there were errors in the lag spacings of up to ten percent of the unit spacing. To overcome this, we developed a calibration method using astronomical sources which corrects the effects of the non-uniform sampling as well as gain error and dispersion in the correlator.