Homebrew Sector Antenna for Wifi ISM band (2,4GHz)

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

The design was published by Dragoslav Dobričić, YU1AW.

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

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 Access Point (or wireless Router) or Wifi client with equal benefits.

Properties

This antenne has the following properties.

Frequency 2,4 to 2,5GHz

Impedance 50 Ohm @ 2,45GHz

VSWR < 1:1,5

Polarisatie Verticaal

Vertical beamwidth (-3dB) 15º

Horizontal beamwidth (-3dB) 125º

Connector: Female-N type (50 Ohm)

Principle

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

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)

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.

For the reflector, use 455x62mm of Copper-clad circuit board. Copper side must be on the same side as the radiator (I use double-sided PCB).

Drill a hole in the centre to accept your N-Type connector. I Use 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!

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

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

Solder the radiator to the coax feed/ BALUN.

Screw or rivet the PE studs to the radiator.

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

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

Links

http://www.qsl.net/yu1aw/ VHF/ UHF Antennae by Dragoslav Dobričić, YU1AW

http://www.brest-wireless.net/wiki/materiel:amos Brest Wireless AMOS Antenne pagina (French)

http://www.wirelessnederland.nl Wireless Nederland – Infinite well of knowledge on the subject of Wifi (Dutch)

http://forum.wirelessnederland.nl/viewtopic.php?t=8128&highlight= WLNL: Drie AMOS Sector antennes voor Wireless Pinkster Kamp 2006 (Dutch)

http://forum.wirelessnederland.nl/viewtopic.php?t=7428 WLNL: Zelfbouw 125° 12dBi Sector antenne uit Servië (YU1AW) (Dutch)

Disclaimer

I will not be responsible for damage to equipment, your ego, personal injury or worse that may result from the use of this material and material found on any links on my pages. You are responsible to make sure that your use any of my designs is legal in your country.

PE2ER Homebrew projects page

Version: Nov-2007