PROGRESS TOWARDS A LÜNEBURG LENS SOLUTION FOR A LARGE, WIDEBAND, MULTI-BEAM ARRAY RADIO TELESCOPE Graeme James , John Kot, Andrew Parfitt, Nasiha Nikolic CSIRO, Telecommunications & Industrial Physics, PO Box 76, Epping NSW1710, Australia Email: first name.last name@csiro.au ABSTRACT The Lüneburg lens has been identified as a candidate antenna element for the Square Kilometre Array (SKA) radio telescope. As the important attributes of such a lens approach have been articulated elsewhere, we present in this paper an update on the work in progress to determine whether or not such a solution to the SKA is economically and technologically feasible. Given that there are many issues associated with the array itself that are common to any solution to such a large problem, we concentrate on three areas of particular concern to the Lüneburg lens solution. INTRODUCTION The SKA radio telescope [1] is planned for construction around 2012. With an effective collecting area likely to be around one square kilometre, this enormous array to study the early universe at centimetre wavelengths will complement next generation telescopes operating at other wavelengths. From the outset there has always been the desire for the SKA to provide a distinctive capability (aside from increased sensitivity) not currently available on any other radio telescopes. To this end, one possibility is that of having a multi-beam instrument with several independent beams anywhere on the sky at any one time has scientific applications as well as opening-up new ways of how one observes the radio sky. This multi-beaming capability was the major consideration behind the NFRA proposal for a phased array as the SKA antenna element [2]. While there have been several alternative schemes subsequently put forward for the antenna element, the only other option to-date providing truly independent widely-separated multiple beam capability is the Lüneburg lens proposal outlined in [3], [4] and illustrated in Fig. 1 below. All the other proposals have, in principle, limited multi-beaming capability, ranging from the cylindrical reflector ‘doublet’ [5] where multi-beaming is possible within a fan beam, down to multi-beaming within the main beam of a conventional reflector antenna [6]-[8]. From the outset cost has been a major parameter driving the design. To build the SKA at an affordable price within the next 10-15 years, heavy reliance is being placed on Moore’s law, the economies of scale and some clever engineering. Another major consideration is upgradeability. In building such an expensive multi-national telescope, the ability to readily upgrade and extend the instrument’s capability over its lifetime is an obvious attractive feature in any design. In this regard, the Lüneburg lens approach has a distinct advantage over all other proposals. We consider now three areas of particular concern to the Lüneburg lens solution. Focus f D 2θ max Focal surface Figure 1: Lüneburg lens focussing an incoming plane wave