Linear Focus Parabolic Wi Fi Antenna
Building A Basic Reflector For Extending Wi Fi Range
Parabolic wifi antennas are generally thought of as dish shaped objects, fed by a yagi, biquad or helical radiator at the focal point. These dishes are curved in three dimensions and involve considrable effort to construct from scratch. An alternative is the two dimensional "linear focus" reflector. It focuses energy along a "focal line" instead of one point, and works quite well with simple dipole antennas. Design is as simple as selecting a suitable parabolic curve, plotting it on a flat surface, and fitting a sheet of mesh or solid metal to the parabola.
Doing the design calculations by hand is quite time consuming; there is excellent software enabling one to create a template and in minutes. For doing the calculations, one good parabolic antenna calculator is HDL_ANT. Another very useful calculator, called Parabola, was designed originally for solar cooking, and can be used for making wifi network antennas. When using these, bear in mind that the f/D ratio (focal length /diameter) should be between 0.3 and 0.6 for optimal performance.
This linear focus parabolic wifi antenna consists of a sheet of metal shaped to precisely fit a two dimensional parabolic curve. Gain is about 15 dB over a dipole, and depends greatly on quality of construction. Of greatest importance is shaping the sheet metal to accurately follow the parabolic curve given in the template. Parts may be found at large hardware retailers such as "Home Depot" or local scrap metal dealers. Versions of this antenna have been made using automotive sheet metal; others use wire mesh. Whatever the material: follow the curve!
This antenna can be built in a couple of hours and involves a fair amount of measuring, cutting, bending, and bolting metal. Use caution around the sharp edges when finished, put it up and enjoy a very durable antenna that provides great signals.
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 wifi antenna template,
Another parabolic wifi antenna
Rear view of the linear focus
This antenna can be constructed in a couple of hours and some measuring, cutting, bending, and bolting metal. Use caution around the sharp edges. When finished, put it up and enjoy a very durable wi fi antenna that provides long range and high bandwidth connectivity.
- Mark all flats and flashing from edge to edge along their centerlines and across midpoints, both sides.
- Mark dots on flat "A" along its centerline, at the 1," 18," and 35" points. Carefully drill holes at these points.
- 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.
- 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.
- 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.
- 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.
- Use the hacksaw to cut flat "B" at the third mark.
- Mark across flat "B" at 7 1/2" from its long end (halfway to its first bend)
- 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"
- 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.
- Clamp the flashing onto "A" along the inside of the curve, carefully along the center lines, and drill through the existing holes near the ends of "A," making holes in the flashing. Insert the short screws through the flashing and "A." Apply nuts and tighten securely.
YOU SHOULD NOW HAVE A PARABOLIC REFLECTOR WITHOUT A MOUNT
- Carefully drill through the existing holes in the center of "A," making 3 vertical holes in the center of the flashing, 1/2" apart.
- 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.
YOU SHOULD NOW HAVE A PARABOLIC REFLECTOR that can accommodate a USB wifi adapter along the focal line.Mount the assembled reflector and adapter in a window, on a balcony, or wherever there is a line of sight path to the desired wi fi access point.
For best performance, consider using a biquad feed. Other choices include using a colinear dipole, or using a 6" length of PVC to place a USB wifi adapter in front of the reflector. An alternative for systems not needing huge amounts of gain is the very simple - and smaller - linear parabolic on binarywolf.com. It enables extended range 802.11 connections better than the dipoles supplied with a lot of equipment.