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The concept of super-resolution refers to various methods for improving theangular resolution of an optical imaging system beyond the classicaldiffraction limit. Although several techniques to narrow the central lobe ofthe illumination Point Spread Function have been developed in opticalmicroscopy, most of these methods cannot be implemented on astronomicaltelescopes. A possible exception is represented by the variable transmittancefilters, also known as "Toraldo Pupils" (TPs) since they were introduced forthe first time by G. Toraldo di Francia in 1952. In the microwave range, thefirst successful laboratory test of TPs was performed in 2003. These firstresults suggested that TPs could represent a viable approach to achievesuper-resolution in Radio Astronomy. We have therefore started a projectdevoted to a more exhaustive analysis of TPs and how they could be implementedon a radio telescope. In the present work we report on the results of extensivemicrowave measurements, using TPs with different geometrical shapes, whichconfirm the correctness of the first experiments in 2003. We have also extendedthe original investigation to carry out full-wave electromagnetic numericalsimulations and also to perform planar scanning of the near-field and transformthe results into the far-field.

Laboratory measurements of super-resolving Toraldo pupils for radio astronomical applications