Lutenna - The antenna made of Sugar

Grodsik

A half lens on top of a metal plane has the same multisat capability as the full sphere.

I'm thinking of building one out of polypropylen (PP), DC = 2.3, and loss tangent = very, very low at most frequencies. Any experiences?
The actual material I'm considering is cheap PP rope, and either tie the rope in a large ball, or cut the rope in short pieces (fibres) and fill a half sphere container with it. Since the size of the fibres is much smaller than the wavelengts one can use the packing density of the fibres to control and lower the DC value by 20-30%....

Any thoughts if this is viable?


Thanks for a good thread!

Satcom1

Casser- very interesting design.

Data on dielectric constants of gasses.

_http://www.iop.org/EJ/abstract/0950-7671/43/3/313

I am not a complete idiot, some parts are missing.

Satcom1

Casser-

Consider that that a sphereical dish lackes a well defined focal point and a parabolic dish has a well defined focal point. These things (antenna) are Lenses and maybe a parabolic shape rather then dome will give a good focus point on the LNBF. However, it seems you would not have a multi-satellite lens.

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I am not a complete idiot, some parts are missing.

g_c

Dear Casser, this is a very interesting topic. Can you post your pdf file here. I couldn't download it from Dragteam.info forum (and put more pics here, please, if possible).

rolfw

Raven made one of these Luneberg Lens units a few years back, but I believe couldn't get the dome manufactured for the right price and quality to make it viable, so never went to production with it. They did however have working prototypes which they displayed at a couple of shows.

luneberg lens

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g_c

use "Coke" instead of sugar?? Its dielectric constant is ranged from 1.1 to 2.2

casser

Hi..

Unfortunately since April i stopped the project..but i hope that in August start working on it again.

Some people from Portugal and Brazil made the antenna with different materials, but nothing new, sugar and granulated Polystyrene are confirmed materials but nothing more. Also like i said before, bigger antenna versions using only one dielectric material doesnt perform any good..a 40cm version work like a 25/30cm.

Maybe the Loss Tangent is messing up in bigger versions, since the signal must pass throught a lot more material (remember that doubling the diameter of the antenna, you will not double the volume of the antenna..is a lot more!!).

The PDF file have some mistakes, but 90% of the information is here in this topic..i´ll try to make a new PDF.

@Satcom1, i think that these sphericall antennas have good FC..since is much more critical to find the FC in a sphere rather than in a Dish and since my version of 20cm can achieve 120% efficiency with a normal LNBF...maybe bigger versions need another type of Horn, with different aperture? But your idea is good to try, maybe in a simulation software first?

A Portuguese video of the antenna (made by Houls, user from Dragteam.info)
_http://www.youtube.com/watch?v=l8_LbCmZfLQ

New farragsat 40cm version
_http://www.youtube.com/watch?v=auwm-yQWHQ8

1ºpicture-> a 25cm VS 40cm, same performance.
2ºpic-> 25cm version
3º My homemade half-ball, bad results

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ldc

Really cool idea.. Have been reading about this for a few hours now.. One thing i came up on was that we also need to consider the Loss Tangent of the materials used.

So, what type of things are out there that have a low loss tangent at the needed frequencies and has a temperature-stable dielectric constant within the wanted range that's relatively cheap and is easy to obtain?

I'm thinking that a gas is probably the best and easiest since mixing 2 powders will most likely result in an uneven mixture in different areas of the globe, also we should see what types of different globes are out there since that will also affect the performance, but i suspect that the loss tangent is the most important for the globe since the sphere will be quite a low percentage of the whole system.

Maybe if someone is feeling up to he could create some graphs of the theoretical gain of different gasses with this?

Some interesting reading:
_http://books.google.se/books?id=P2cLPsLDHxcC&lpg=PA16&ots=yOjRArwY8X&dq=% 22Loss%20Tangent%22%20%22dielectric%20constant%22& pg=PA22

Just a few crazy ideas for the contents:
- Fill the sphere with different types of balls with a low loss tangent but a bit higher dielectric constant. (Can we get the dc to the target range?)
- Pure CO2 has a DC of 1.6 but have not found any loss tangent for it.
- Any cheap noble gases with a low DC out there that we could use to mix a cheap high DC gas with? Probably need to keep the weight of the gases approximately the same.
- Can we maybe lower/raise the pressure in the sphere to lower raise the DC? Get a high DC gas and lower the pressure is probably the best way to go since that would reduce the loss tangent. But with this we would have to have a bit sturdier sphere.

Maybe the creator of the thread could create a table that we could fill up with information on DC/LT on the different materials?

Just some crazy ideas from a insomniac so don't take it word for word

ldc

Did some more reading about this on another one of these sleepless nights...

Not shure about this, but from my understanding it seems like if you dont use multiple layers you will get a larger focal-point when increasing the size of the sphere and this might be the problems that where noticed initially when a larger sphere resulted in less performance. It could be possible to overcome this to some degree with having a lower DC for larger spheres ie increase the distance to the focalpoint but it might be tricker to get correct alignment of the LNB when doing that.

And just a thought about this, maybe someone that already has a large sphere could do a simple test with adding a simple horn to the LNB and see what that would do to the reception.. (some simple cardboard+aluminum foil design).

One idea i had about making a multi-layer thingy..
Get a number of bowls, place bowl and fill with styrofoam (mixed with some material that will change the DC of it), first layer done, get the next bowl and place over the first layer and fill up with the next layer and repeat (removing each bowl when going to the next layer).. Could be an easy way to do it... just gotta find out a way to make styrofoam at home

And as said before... crazy insomniac at work here

Trust1

Just a thought of me , what kind of feedhorn will perform the best ?
I think the one designed for a prime focus dish .

My soldering iron is smoking all the time .

Gr. Trust1

ldc

That would depend on how large the focalpoint is so i think a basic horn-antenna (http://en.wikipedia.org/wiki/Horn_antenna) should suffice for the test..

About the focal-point... Think of it this way. When having center at DC 1.0 and outer layer at 2.0. When the radiowaves gets reflected at the outer-layer of the sphere it will bend correctly to get to a good focal-point, but when it goes closer to the center it will weer off a bit more than wanted and with a simple feedhorn you could try and get a bit more signal into the LNB.

A non-tuned feed-horn will probably not do much with this, but it would be nice to see if my theory about this is correct and in that case try and make a tuned feedhorn for it, but this is probably gonna increase the noice-levels. Might not be good for weaker signals out there but it could possibly help to have a larger sphere to compensate when raining or snowing.

ldc

oh, forgot a link..
http://wwwatnf.atnf.csiro.au/project...um2004/JSK.ppt

some nice ideas that maybe we could use, and maybe some ideas to make us be able to make a multi-layer version even

normsky

Actually common satellite dishes are in the shape of a circular paraboloid. Which most certainly isn't what is produced by cutting a section from a sphere.

Only waves origininating at the center of the sphere would all be reflected to the same point. Pretty useless for focussing parallel waves from a distant source.

As far as the sugar is concerned I was very interested to read this. Shame I saw it so late in the day.