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I'm intrigued by this, and how it would work:- 3 sub-questions if I may:

  1. Construction: As I understand it's a flexible sphere constrained by a rigid edge.

    a. Do we simply glue 2 flat circular pieces of flexible material together at the edges and inflate? (e.g. the inflatable dish on PE1RAH) Or,

    b. do you have to cut out sections to make it parabolic, and the inflation simply gives it the rigidity? (e.g. page 4 of this document)

  2. Spherical Antenna, as manufactured by e.g. GATR. Would the design for this inflated dome with internal parabola be in effect 2 inflatable structures - 1 sphere (to give rigid circumference, and an internal parabola as in question 1, or could you do something like this with only 1 inflatable structure?

  3. Design. I'm assuming the parabola generated using question 1.a would be a factor of gas pressure + stretch of fabric given there is no slack in the material? Or are other factors involved?

Any suggestions for design or theory papers would be most appreciated. I'm going to have a try at building one of these for portable wifi :)

Thanks

EDIT: I just threw together a prototype from 2 plastic bags/drinking straw/tape - it's a bit rough to see a definitive answer, but looks parabolic.

EDIT 2: on further digging, I confirmed that the inner parabola in a spherical antenna holds its shape by continually topping up the pressure in the 'top' of the sphere to keep the parabolic shape bowed the right way.

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up vote 2 down vote accepted

When You look with an "math eye" at the shape in Your first link, You will see that the form is more a part of a sphere, as theory predicts.

In second link there is a picture of the parabolic mandrel which was used to form the foil. The pressure will not deform the foil much, just keep it inflated.

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Thanks. that's a lot clearer now - I missed the mandrel in my quick glance at it. Any thoughts on the Q3. How one would inflate a sphere with a parabola inside it? I still think the internal parabola must be a second balloon at a higher pressure internal to the sphere –  velniukas Apr 17 '11 at 11:04
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