Super resolving systems: Toraldo Pupils

(PUTO Project)

 

Electromagnetic numerical simulation at 20 GHz *

(FEKO full-wave software)


  Three coronae Toraldo Pupil

                          

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Near field

 

 

Left:. FEKO model for simulating a 3-coronae Toraldo Pupils (TP). The central green cylinder represents the dielectric layer (with refractive index n = 1.5) employed to implement the phase inversion.

 

Right: FEKO model for a 3-coronae TP using the planar multilayer substrate option, which simulate an infinite opaque  screen.

 

 

 

Left: Modeled distribution of the near-field for the 3-coronae TP using an incident (from right) plane wave.  Multiple diffraction rings are visible. The diameter of the open pupil and the circular screen are 9 cm and 40 cm, respectively.  The near-field has been computed  at a distance from the screen of 20 cm. The screen thickness is one wavelength (1.5 cm).

Right:  Same as to left  for an incident field generated by a rectangular feedhorn with edge taper.  The edge diffraction effects have disappeared. The logarithmic color scale are from 20 dBV/m (blue)  to 0 dBV/m (red).

 

 

Left: Modeled distribution of the near-field for the open pupil.

 

 

 

Right: Modeled distribution of the near-field for the 3-coronae TP.

 

 

 

Far field

 

Left:. Plot of the amplitude in the far-field of the 4 coronae TP (redline), together with the comparison with the amplitude distributions of the open pupil (blue line) and 3-coronae TP (green line).

Right: FEKO simulation showing the amplitude of the far-field  for the 3-coronae TP model, using a rectangular feedhorn source  whose field is incident on a circular finite screen (red curve, with higher sidelobes),  and a plane wave with the planar multi-layer substrate option (green curve).

 

 

 

Left:  FEKO simulation showing the amplitude of the far-field for the 3-coronae TP model (green line), using as a source the equivalent “aperture excitation” fields obtained at the Cassegrain focus of an antenna whose aperture diameter was 3.2 m and the same f/D as the Medicina antenna (hence f = 9.72 m). For  comparison is also shown the far-field of the open pupil (blue line).

 

 

 

Right: Optical system used in the simulation to left. The black bar at the bottom represents the Cassegrain focus, which coincides with the focus of the plano-convex lens. The latter converts the expanding spherical wave into a plane wave that intercepts a TP and generates the near-field shown. The lens has a radius of curvature of 28 cm, a diameter of 25 cm and a thickness along the optical axis of 3 cm. The separation between the lens and the planar multi-layer substrate screen has been reduced in the figure for the sake of clarity.  The real distance used for this simulation was 150 cm.  The gain in angular resolution, as measured by the ratio of the widths of the central lobe, is of about a 2 factor.


*For a detailed description of the results see:

  Luca Olmi et al.,  Super-resolution with Toraldo pupils: analysis with electromagnetic numerical simulations”,  Proc. SPIE 9906, Ground-based and Airborne Telescopes VI, 99065Y (July 27, 2016); doi:10.1117/12.2230970