A Cardboard Horn for 802.11b
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Fun. Well, it doesn't stand the rain yet, but it is easy to build and gives you a lot of dB.
The waveguide that feeds the horn is the bottom of a Tetra Brik (see MicroTVAerial). The horn is made of cardboard covered inside with kitchen aluminium foil.
The images are still in Belgium... maybe a local copy would be faster
The box is 42x25x25 cm (16-1/2 x 9-7/8 x 9-7/8 in.). The horn's aperture is about 25x25 cm². The Tetra Brik bottom is about 8.5 cm (3-11/32 in.) long (the ~3 cm (1-1/8 in.) rod is at about the middle). Four pieces of cardboard covered with aluminium foil make the horn. They are about 32 cm (12-9/16 in.) long. Their big side is 25 cm (to match the box side), and the small sides match the milk box (6.5 cm and 9.5 cm, or 2-1/2 and 3-3/4 in.). You can find some theory in "The W1GHZ Online Microwave Antenna Book".
...And the results speak for themselves
Of course, maybe it would be better to use something other than cardboard, but it was so easy. I seem to get 12 dB more than with a Ricore can (diameter ~10 cm or 3-15/16 in.). When one knows that with 6 dB one gets double the gain, here I multiply the distance by four (with one horn). With two Ricore cans, we made more than 5 kilometers, Liege 2002.04.01; sorry, it is in French, so...
15 Jun 2002, we tested two of these horns at 9.5 km (~6 mi.), Liege2002.06.15 (in French). One horn with various antennae:
a Ricore Mouseline can,
a [MicroTVAerial] with 20 elements (~67 cm or 26-3/8 in.), and
Here are the results:
Note that the noise figure is unusually high (usually, it is around -100 dBm). In this British horn, he choose a cut-off frequency of 2 GHz with a waveguide internal dimension 76 x 38mm (3 x 1-1/2 in.) to reject 1800 MHz cell phones. It would be interesting to see if it helps.
Here are the 'principles' of a horn design:
There is also a Cardboard Horn Antenna Designer (beta version?).
Of course, when you have space, you can build a bigger one.
g0mrf uk horn
images.google horn antenna
The Ricore can is based on the saunalahti.fi antenna2.
--xof (Liege, Belgium 02 Jun. 2002)