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ARIES is a new imaging riometer offering enhanced spatial resolution compared to our existing imaging riometer (IRIS). Unlike IRIS, ARIES is based on a Mills Cross antenna configuration. Enhanced digital signal processing enables ARIES to achieve a significant increase in spatial resolution whilst sufficiently suppressing the sidelobes inherent to a Mills Cross based system configuration.

ARIES schematic overview

Figure 1: ARIES schematic overview

Figure 1 shows a schematic overview of ARIES. The signals from the two arms of the Mills Cross antenna array are fed into two separate Butler matrices, one for each arm. Each output of the Butler matrix forms one fan shaped beam. Figures 2 and 3 show one example of a fan beam formed by the Butler Matrix for the North-South arm and one example of a fan beam formed by the Butler Matrix for the East-West arm of the Mills Cross antenna array, respectively.

You can also watch an animated version of figure 1 or an animated version of figure 2.

ARIES arm 1 fan beam

Figure 2: a fan beam from arm 1 [animate!]

ARIES arm 2 fan beam

Figure 3: a fan beam from arm 2 [animate!]

The final narrow beams (so-called pencil beams because of their pencil-like shape) are formed digitally by means of cross correlation. Cross correlation detects the signal that is common to the signal of two perpendicular fan shaped beams, and this common signal is the signal coming from the direction where these two fan beams intersect.

Thus by intersecting each fan beam from the North-South arm with each fan beam from the East-West arm, we get many pencil shaped narrow beams over the whole field of view. Figure 4 shows an example pencil beam, together with the two fan beams that were used to create this particular pencil beam. You can also watch a movie showing several pencil beams.

pencil beam

Figure 4: a pencil beam is formed [animate!]

Two perpendicular arms of 32 antennas each theoretically provide the same spatial resolution as a 32 by 32 filled antenna array. As the sidelobe performance of such a system is worse than that of a filled array, tapering reduces this resolution slightly. Still, a resolution at least equal to that of a 16 by 16 element filled antenna array is achievable, with only a quarter of the antenna elements that would be required to build a full 16 by 16 element phased array.

Data from various prototype stages has been collected starting from 2002, and the current system with fully digital beamforming went live in March 2007.

ARIES Overview Poster Thumbnail

You may be interested in downloading a PDF version of a poster on ARIES (3.5MB), or have look at the very-low-resolution bitmap preview (140KB).

See the following links for more information about ARIES:

 Contact: Prof. Farideh HonaryM. Grill
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