Progress on Luneburg lens development
The main Australian proposal for the SKA antenna element utilises the multi-beaming capability of the Luneburg lens. This lens is basically a spherically symmetrical ball of graded dielectric such that the incident field is focussed by the lens to a point on its' opposite side. Given the spherical symmetry, any angle of incident field is focused to a point on the focal surface surrounding the lens. Hence, it is naturally a multi-beam scanning antenna by providing one feed per beam and tracking a source by feed movement.
To construct the lenses for the SKA out of conventional dielectric materials is not a viable proposition given weight, loss and cost considerations. From the outset, the CSIRO SKA proposal utilising the Luneburg lens has been dependent on the successful development of artificial dielectrics where weight, loss and cost are reduced considerably compared to currently available materials. Currently, a joint project between four CSIRO divisions (CTIP, ATNF, CMS [CSIRO Molecular Science] and CMST [CSIRO Manufacturing Science and Technology] - the latter two divisions based in Clayton, Melbourne) is underway to develop suitable artificial dielectric materials for constructing the Luneburg lens. While details cannot be given here as there are patents pending on some of the processes involved, in outline, low density low loss foam is being doped with graded small amounts of high dielectric low loss ceramics such a Titania to produce artificial low loss, low permittivity dielectrics. Some sample material has already arrived from Melbourne and over the next few weeks we expect to assess many more samples. Our colleagues in Melbourne are very confident they can produce what we want and are participating in the project with great enthusiasm.
Aside from the work on artificial dielectrics, work is in progress on the electromagnetic and mechanical design of the lens and associated feed system. For the next issue we should be able to report on some tangible results from all of the above investigations.
Graeme James
(Graeme.James@csiro.au)