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Homebrew Sector Antenna for Wifi ISM band (by Pe2eR)


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On this page you will find information on how Pe2eR builds a sector antenna for de Wifi 2,4GHz ISM band.

The design was published by Dragoslav Dobri?i?, YU1AW.

Most of his work is in Serbian, but Dragoslav and Pe2eR have corresponded in English. they differ a little about the dimensions of Dragoslav AMOS antenna. When Pe2eR build the antenna as Dragoslav describes, it usually has best VSWR below the Wifi band, so Pe2eR shortened it a little.

So now this antenna is suitable for use in Computer Radio LANs conforming to the IEEE 802.11b/g standard – better known as Wifi. It can be used on an a La fonera Router or Wifi client with equal benefits.

The properties

Frequency: 2,4 to 2,5GHz

Impedance: 50 Ohm @ 2,45GHz

VSWR: < 1:1,5

Polarisatie: Verticaal

Gain: 11dBi

Vertical beamwidth: (-3dB) 15º

Horizontal beamwidth: (-3dB) 125º

Connector: Female-N type (50 Ohm)

Principe

The antenna is a centre-fed broadside array antenna, based on the Franklin Antenna as published in Rothammels Antennebuch (shown below)

Franklin.jpg

This is the complete design in Serbian as published by YU1AW: Amos.zip (3,7MB)

This is my version of his design. Overall, the dimensions are a little shorter:

Construction drawing in Windows Metafile format (best viewed with Win XP fax and image viewer)

Construction drawing in Autocad format

Building the antenna step-by-step.

Make a hardcopy of the Autocad drawing (the antenna is drawn to scale 1:1).

Use 292.2mm of approximately 1.8mm diameter copper wire for each radiator. Stretch wire (to straighten it). This wire is commonly used in Dutch house wiring. Put the wire along the linear scale on the drawing and mark it as shown (I use a permanent CD-ROM marker)

DraadAftekenen.jpg

Next, prepare 4 pieces of PE studs. Use the insulator from RG-213 – like cable. Each stud is 15mm long. Drill a 2mm hole 10mm from the end.

AfstandBus.jpg

For the reflector, use 495x62mm of Copper-clad circuit board. Copper side must be on the same side as the radiator (Pe2eR used double-sided PCB).

Drill a hole in the center to accept your N-Type connector. Pe2eR used one that comes with rigid coax attached. The shield of the coax should extend to 28mm above the surface of the PCB. The centre conductor must extend 5mm more. Drill 4 holes to attach the studs to the reflector.

Bend the two radiators. Do not forget to slide on the PE studs before bending. Remember: It is the amount of wire you use that is important, not the final dimensions after bending!

stralerbuigen.jpg

Fabricate the 1:4 BALUN from ½ wavelength of coax (measured by the shielding).

RG-316 (v=0,697): 43mm (This is the coax cable I use here)

RG-58 (v=0,66): 40,7mm

CFD200 (v=0,83): 51mm

BALUN.gifWifiSectorAntenneBALUN.jpg

Verbindingen KORT houden” means “keep connections SHORT as possible”.

Solder the radiator to the coax feed/ BALUN.

WifiSectorAntenneFeed.jpg

Pe2eR used S-Lon 65mm mini PVC rain gutter to house the sector antenna. Pe2eR is sure that this is not available all over the world, so you need to find something similar.

WifiSectorAntenneS-Lon.jpgAMOSinMast-Small.jpg

Pe2eR has also used this antenna without a radome. It is however very susceptible to mechanical damage.

Note

On the up an comming WirelessPowerKamp-2008  event, the FON WPK-network will be connected to the sector antenna's

Gerard (with thanks to Pe2eR)

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The Build of the 3 (AMOS) Sector antenna's for the WirelessPowerKamp

Here some picture's of the build.

baluns.jpg

printplaat.jpg

reflectorenenbehuizing.jpg

stralers.jpg

What brings it too this.

samenbouw.jpg

Next is fitting the "radome" protection on the antenna'

hardware.jpg

(the iron parts is for mounting the antanna's)

And the final mounting of the antenna's must be something like this:

ophangen.gif

(Again with a big thanks to Pe2eR)

:lol:

Next up is building a butget all weater caseing for mounting in the La Fonera's with out to have to take the La Fonera's apart, but still with a external antenna mouning point and a P.O.E (Power Over Ethernet) feeding.

Will follow up with this project some time soon.

In the mean time just have fun in your live.

:wink:

Gerard

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