INTRODUCTION
In the period august-december 2001 the installation of an active surface has been completed on the Noto radiotelescope (Sicily) www.ira.noto.cnr.it, operated by Istituto di Radioastronomia-CNR (via Gobetti 101, 40129 Bologna, Italy). The project was funded in 1999 by MURST (Ministry of the University and Scientific and Technological Research) in the framework of Enhancing the Italian Scientific and Technological Network, Radiaostronomy Cluster, with title "Strenghtening of the Noto radiotelescope - Extending its observing capabilities to the millimeter radiowaves".
The active surface concept aims to compensate gravitational deformation effects of the antenna backup structure by moving the panels forming the antenna primary mirror. The deformations of the surface reduce the antenna gain at the elevations other than elevation where the panels alignment is done, and the effect is worst as the frequency increases.
The Noto realization provides an open loop system to move panels by means of electromechanical actuators, where a computer updates the mirror position such that a parabolic shape is maintained at all elevations. As a result the antenna gain curve is flat with respect to the antenna position.
In order to increase the antenna gain peak value old panels were substituted with new ones more accurate.
The original design of the Noto antenna provided a frequency for maximum gain equal to 5GHz, the aim of the active surface project is to increase this value, reaching an almost full efficiency up to 45GHz. Doing that a new scenario should be available to use the antenna, also up to 86GHz.
It has to be underlined that all the design has been made in house, lacking on the market commercial device and systems able to fulfil the requirements and constraints coming from the requested accuracy of the application.
Moreover this realization can be seen as an upgrade of an existing telescope and as a prototype of the incoming Sardinia antenna (SRT,64m) http://www.ca.astro.it/.
