Waveguide theory
Antennas transmit or receive radio energy through a driven element. The length of the element determines the frequency. The energy can be directed in a certain way by other elements of the antenna; the improvement of a particular direction is referred to as the gain of the antenna. Note that there is no amplification of the signal — the signal is just concentrated in a particular direction, to the exclusion of others.
Waveguide antennas have the driven element in a metal tube, with one end closed and one open. The simplest designs have a cylindrical tube, with one end covered with a flat metal reflector and the other left open. The placement of the driven element is critical, as is its orientation (vertical or horizontal) after the antenna is mounted.

Does size matter?
The diameter of the cylinder determines what frequencies the antenna will pick up or transmit. The length of the cylinder needs to be mathematically related to the diameter; this means that a random cylinder diameter/length combination is not likely to work, or will work at undesired frequencies. The attached OpenOffice spreadsheet that will help you determine the correct combinations.

Waveguide calculator
As mentioned above, there are no appropiately sized cans on market shelves in Mali. There are, however, perfectly sized plastic bottles. The Diago brand in particular lends itself to bottle-making. Not only is the bottle the correct diameter, and long enough to cut back to achieve a specific wavelength; it also has plastic moldings in exactly the right positions for inserting the probe, and cutting for a single wavelength.
A test in a microwave oven found that the plastic this bottle is made of is virtually microwave transparent. The only problem is that the bottle will not reflect microwaves, the fundamental duty of a waveguide antenna.

Enter flyscreen, which is readily available and inexpensive in Mali. Its mesh is a 1-millimeter weave; this is small enough, when compared to the wavelength of wireless networking frequencies, that it appears at those frequencies to be a solid reflective metal surface.
In summary, BottleNet is a design that uses a bottle like Diago’s for the shape and rigidity, and flyscreen mesh as the metallic reflective surface.

Manufacture/Ingredients

You will need:

• A 1.5 litre bottle of Diago mineral water
• A piece of metal woven flyscreen 300 mm x 220 mm (for the cylinder)
• A piece of metal woven flyscreen 100 mm x 100 mm (for the end reflector)
• A 31 mm length of 14 or 16AWG wire (for the driven element)
• An appropriate connector (N-type female bulkheads are great but not so easy to find)

Handy tools:

• Pliers
• A drill bit or sharp pointy object for probe insertion through plastic bottle
• A soldering iron and solder
• Scissors or wirecutters for cutting mesh
• Leather gloves for handling sharp edges of flyscreen, and/or Band-Aids for failing to take this advice

Method

1. Drink the water from the Diago bottle. Remove the label and allow the bottle to dry thoroughly.
2. Prepare the end reflector: Ensure the 100mm x 100mm flyscreen mesh will not fray. For at least three edges, roll the mesh over itself, ensuring that there is a flat surface in the center. Put aside for later.
3. Prepare the 300mm x 220mm flyscreen mesh: Ensure one 300mm edge will not fray. Preferably the cut of mesh will have the manufacturing weave edge as this edge; if not, roll the edge over itself.
4. Using the 300mm x 220mm flyscreen mesh, wrap the outside of the bottle. Use the non-fraying 300mm edge toward the top of the bottle. Bring the two 220mm edges together, and roll them down over themselves until they are mechanically joined. Ensure the final roll leaves as flat a surface on the inside of the cylinder as possible. NB: it is very important to wrap this cleanly, so that the same horizontal wire meets itself on the other side of the join. This will greatly assist the reflector positioning later.
5. Mark a length of as close to 208mm as you can down the cylinder, with an overhang at the base of the bottle. Aligning this mark with the actual bottom edge of the bottle should leave the top reaching just to the very top of the plastic moulding of the Diago logo.
6. Fray the mesh from the 208mm mark to the end (about 12mm) by removing horizontal wires (ie, ones going around the bottle) until the vertical wires stand upright. It is worth putting in time at this point to make sure all the wires are straight and parallel — in particular, that they do not cross each other. Spending time doing this now will save a huge amount of frustration in the next step.
7. Affix the end reflector prepared earlier. Feed the frayed wires from the cylinder into the reflector, keeping it as circular as possible. Push the reflector down as far as it will go (i.e., so it is as close as possible to the 208mm mark) ensuring it is square to the line of the cylinder.
8. Adjust the position of the bottle in the mesh cage so that the bottom rests lightly on the reflector, without distoring the plane of the reflector.
9. Prepare the driven element: solder the 31mm length of wire into the center core connector hole in the Appropriate Connector. If soldering is not available, this needs to be as fitted as possible with a good electrical connection and unlikely to come loose.[NB: If it is made using 16AWG gauge wire, the probe will fit very tightly into the centre core connector hole. As such, solder may not be necessary. It may be enough to place the probe in the hole, then either place a single drop of Superglue on the core hole or just lightly crimp the metal around the hole onto the probe. *Ensure the probe wire is as straight as possible, and pointing directly away from the appropriate Connector. *Measure the probe length again. This length is the most critical one in the entire design, and performance can greatly vary with tiny variances.
10. Drill a hole for the driven element. The hole needs to be as close as possible to a distance of 52mm from the reflector, which is the first point of decorative moulding in the Diago bottle.
11. Attach the probe to the bottle. The outside needs to make good electrical contact with the outside of the cylinder. Affix in place with tape or wire circling the entire bottle.
12. To come: information about mounting.
13. Connect antenna between a radio source and a receiver.
14. Align and enjoy!

Serves 2.4Ghz!

Source: http://mali.geekcorps.org/2005/11/07/how-to-make-a-bottlenet-antenna/

First, find a parabolic reflector designed for Ku band direct-to-home satellite service. These are now inexpensive and abundant - the one pictured above was discarded by a local resident. After washing off the dirt, spiders, and millipedes, I found the dish to be in excellent condition. Similar reflectors can be found in thrift stores, flea markets, and other habitats of electronic scroungers. Seek large reflectors (at least 76cm or 30" diameter), since these will provide greater gain and directivity.

Consider how to feed the antenna. I have seen web pages featuring tin can feedhorns, biquads, patch antennas, and helical radiators. A helical feed seemed suitable for this project as it was simple to build, inexpensive, and provided good gain and directivity. Being circularly polarized, a helical eliminates sensitivity to antenna orientation, and resists attenuation in rain. Though there is a 3 dB loss working linearly polarized stations, designing for more turns brings the gain to parity with the tin-cans and biquads. To Calculate dimensions for your antenna, use this excellent calculator, plugging in a frequency of 2450 MHz.

PARTS REQUIRED:

• one square piece of single sided copper clad PC board for a ground plane
• one PVC kitchen drain tailpiece (3.8 cm / 1.5"diameter) to hold the helical windings
• six 1/8" plastic cable ties
• a length of copper circuit tape (adhesive backed, width 3mm or 1/8") or #14 copper wire
• one suitable chassis connector (I used a reverse sma type matching the connector on my adaptor)
• one 90 degree angle bracket with screws and bolts to fit

CONSTRUCTION:

1) Center the tailpiece on the PC board, copper side, and mark the circumference in ink.

2) Mark four locations on the circumference, spaced 90 degrees, where the cable ties will hold down the PVC tube.

3) Mark one location on the circumference, exactly between two 90 degree markings, where the coaxial connector will be mounted.

At this point you should have a PC board with a circle in the center, four tick marks on the circle at 90 deg intervals, and one tick mark exactly between two others.

4) Drill 1/8" holes on the inside and outside of the circumference at the cable tie locations.

5) Drill a hole directly on the circumference suitable for the chassis connector. Carefully measure and drill other holes for this connector if necessary.

6) Drill four holes, spaced 90 deg apart near the bottom end of the PVC tailpiece.

7) Drill holes to accomodate a small 90 degree corner bracket.

8) Drill holes on opposite side of board to accomodate USB wireless adapter that will be affixed with cable ties.

9) Tin the copper around the connector mounting hole, then mount the connector. Clip the center pin to keep it only long enough for connection to the helix windings.

10) Cut out a notch to accomodate the connector; it should clear center conductor, but avoud cutting out excess PVC material.

11) Feed cable ties through from the back side of the board, through holes in the tube, and back through the board. Tighten the cable ties, making sure the tube is firmly held to the copper ground plane.

12) Use a ruler and the edge of a sheet of paper to create a template for positioning the windings on the PVC tube. Distance zero represents the ground plane, then add the feedpoint distance, then ticks matching the turns spacing. Use the template to mark your tube on both the feedpoint side and the opposite side. The objective here is to have a guide while precisely winding the helix...

Here is a table used for my prototype helix and its connector. Note that turn 1 starts at 0.8 cm (height above ground plane of feedpoint). Turns Spacing is 2.5 cm, and the diameter is 3.9 cm (close enough for 1.5" PVC tailpiece)

13) Carefully wind the helix, using copper circuit tape or wire, then solder to center conductor of chassis connector. Double check against the turns template. Polarization will be right-handed if the turns spiral clockwise (looking outward from feedpoint).

15) Attach the angle bracket and wireless adapter, making sure all parts are secure and ready for service.

The antenna should resemble the prototype, pictured below with the angle bracket removed.

At this point, the antenna is ready for its smoke test...plug in the cables and look for some signals! Theoretical gain of the prototype was about 18 dB over an isotropic radiator; it beat my biquad by about 7 to 13 RSSI units, and indeed seemed less sensitive to polarization and rainfall. Signals still seem to fluctuate much from second to second. If your antenna is functioning satisfactorily at this point, I suggest spray painting two layers of clearcoat onto the windings and groundplane for stability and preventing corrosion.

Currently, I use a short version of this antenna, left hand polarized, to feed a parabolic reflector and note signals about 22 dB stronger than on a simple dipole. Mounting the offset fed dish was tricky - it required inverting the mounting hardware and angling the dish to about 75 degrees to look for signals on the horizon. It rests atop a vertical length of 2" sch 40 PVC pipe. After not initially seeing much strength on a station until finding the right elevation, the signal strength suddenly pegged full scale when I aimed it dead-on! Aiming properly in both azimuth and elevation is important with these larger parabolics - you can aim to reject interference as well as maximizing weak stations. Mounting the helix was simply a matter of removing the LNB and (using the angle bracket) bolting the helix into place at the focal point. It was necessary to bend the bracket just a bit to aim the helix at the center of the dish.

Note that a biquad feed would also work well with a parabolic reflector, and would have a slight advantage over a helical - but would show more sensitivity to polarization and rain

Source:http://www.geocities.com/ab9il_worldwide/wifi3.html

This antenna consists of a sheet of metal curved inoto a two dimensional parabolic curve. Gain is about 15 dB over a dipole, and depends greatly on quality of construction. Parts may be found at large hardware retailers such as "Home Depot" or equivalent.

Parts

Parts & Equipment Required:

• one 36" x 2" aluminum flat (to be referenced as flat "A")
• one 36" x 1" aluminum flat (to be referenced as flat "B")
• one 14" x 36" sheet of aluminum flashing
• metal cutting shears
• a yardstick or tape measure
• three 6-32 x 3/4 machine screws (the long screws)
• two 6-32 x 3/8 machine screws (the short screws)
• five 6-32 machine screw nuts
• one drill with a 1/8" bit
• one fine point felt tip marker
• two clamps
• a pair of pliers
• a hacksaw
• Parabolic Template, printed as a poster (3 x 3 = 9 sheets), carefully aligned and taped

A parabolic template, created by Michael Erskine.

Another parabolic template, more suited to a biquad feed.

Assembly Procedure:

1. Mark all flats and flashing from edge to edge along their centerlines and across midpoints, both sides.

2. Mark dots on flat "A" along its centerline, at the 1," 18," and 35" points. Carefully drill holes at these points.

3. Abeam the hole at the middle of flat "A" drill holes on both sides, 1/2" inside of the edges. This results in a row of 3 across the flat at the 18" point.

4. Set flat "A" along its edge, and bend it to fit the parabolic template. Bend a little at a time, working along the length of the metal.

Flat "A" on the template.

5. Mark flat "B" across the 15" point, beyond there by a distance equal to the focal distance on the template, and finally 3" beyond the focal distance mark.

6. Bend flat "B" to a 90 degree angle at the 15" line. Bend flat "B" 90 degrees in the opposite direction at the second mark (representing the focal distance). Flat "B" should now have a right angled "Z" shape.

7. Use the hacksaw to cut flat "B" at the third mark.

Flat "B" on template.

8. Mark across flat "B" at 7 1/2" from its long end (halfway to its first bend)

9. Clamp flat "A" onto the outside of flat "B" such that the three holes in the middle of "A" are on the centerline of "B" AND the middle hole in "A" is on the 7 1/2" mark on "B"

10. Make sure "A" and "B" are perfectly perpendicular and positioned as specified above, then drill through the existing holes an and into "B." "B" will then have three holes through its centerline that match the holes in "A." Set "B" aside during step 11.

Note how "A" and "B" are bolted together.

11. Clamp the flashing onto "A" along the inside of the curve, carefully along the centerlines, and drill through the existing holes near the ends of "A," making holes in the flashing. Insert the short screwsthrough the flashing and "A." Apply nuts and tighten securely.

YOU SHOULD NOW HAVE A PARABOLIC REFLECTOR WITHOUT A MOUNT

12. Carefully drill through the existing holes in the center of "A," making 3 vertical holes in the center of the flashing, 1/2" apart.

13. Place "B" against back of "A," with the Z bend extending under reflector and toward focal line. Line up the 3 holes and insert long screws through reflector, "A," and "B." Apply nuts and tighten securely.

Rear view.

YOU SHOULD NOW HAVE A PARABOLIC REFLECTOR that can accomodate wireless adapter hardware along the focal line. For best performance, I suggest using a biquad feed. Other choices include using a colinear dipole, or using a 6" length of PVC to place a USB wireless adapter in front of the reflector.

Focal line is along index finger.

Front view of the reflector.

This biquad was made one afternoon using some coaxial cable, wire, and aluminum flashing epoxied to part of a plastic DVD case! It provides considerable gain over those dreaded dipoles supplied with a lot of 802.11 equipment.

Source:http://www.geocities.com/ab9il_worldwide/wifi2.html