Hacer Antenna Wifi Biquad Antenna

Biquad Antenna Design
Biquad Antenna Construction

Simple and cheap wifi dish build, junkyard parts plus high power adapter = free Wifi, here are the instructions I used to build mine, http://www.turnpoint. Therefore, this antenna is used in my current stumbling rig. Trevor Marshall's BiQuad Trevor Marshall has posted plans, as well as NEC2 models for his biquad dish feed. The antenna can also be used standalone. I fashioned the reflector from a discarded tin can. The reflector is 123x123mm, with 30mm 'lips' as specified by Trevor for standalone use. For information on connecting a biquad antenna to a wireless radio, have a look at the page on using wireless antennas. When using a biquad to establish a link to another wireless device, you should ensure the polarisation of the biquad is the same as the antenna you are connecting to. Similarily, if establishing a link with two biquads, ensure. My friend Paul had built a biquad and didn't use anything except the copper clad, the copper pipe in the middle, and the element wire. I'm pretty sure he got them from scrap. Instead of buying some expensive N-connectors, coaxial cables, or wifi adapaters, I just used my WRT54GL router and mounted the antenna directly on the router.

HomeUp

Therefore, this antenna is used in my current stumbling rig. Trevor Marshall's BiQuad Trevor Marshall has posted plans, as well as NEC2 models for his biquad dish feed. The antenna can also be used standalone. I fashioned the reflector from a discarded tin can. The reflector is 123x123mm, with 30mm 'lips' as specified by Trevor for standalone use.

One of my latest obsessions is building DIY homebrew WiFi antennas.

Heinz Beans Cantenna

This is the first antenna I built. It's the ubiquitous circular waveguide'cantenna':
I obtained my can by going to my local 99 Cents Only store and buying a can ofHeinz beans, which happened to be desired 3.25' diameter. The resultant methanegas produced from consuming the beans was used to power my soldering ironafterwards.

I will not go into the construction details, as they are very well documentedon Greg Rehm'ssite. Finding his online cantenna calculator rather intriguing, I set out tofind the mathematical roots to his calculations. The result is my own cantennacalculator program, which I wrote in in C++, based on formulae obtained fromthe ARRL Antenna Book. It's available on my freesoftware page; the archive contains both a Win32 console-mode EXE and fullsource code. In addition, Adam Lesser has kindly supplied a binary forOS-X.
Greg Rehm's calculator fixes the operating frequency at Channel 6 (2437MHz),which is the center channel in the USA, giving the best tradeoff if you want tobuild a general purpose antenna which works across Channels 1-11. On the otherhand, my calculator lets you tune your antenna for maximum gain on a specificchannel; this is handy if you want to use your antenna set up a permanent pointto point link. Let's go through an example using my calculator. The syntax ofthe program is
cantenna diameter centerchannel
where diameter is in mm. So to make an antenna optimized for Channel 6 using my3.25' (82.55mm) diameter can, we would invoke it as follows:
D:>cantenna 82.55 6
Lincomatic Circular Waveguide Calculator V1.1 (Feb 25 2004 23:03:31)
Waveguide diameter: 82.550000 mm (3.250000 in)
Channel: 6 (2437 MHz)
TE11 Cutoff (MHz): 2128.387692
TM01 Cutoff (MHz): 2779.953846
Guide Wavelength (mm): 252.566154 (9.943549 in)
Operating wavelength (mm): 123.017012 (4.843189 in)
1/4 Guide Wavelength (probe to back) (mm): 63.141539 (2.485887 in)
Probe Length (mm): 30.754253 (1.210797 in)
probe pos (Ch1): 66.046774
probe pos (Ch11): 60.564048
probe pos (Ch14): 58.520674
difference between Ch1-Ch11 (mm): 5.482725
So what's the meaning of all this gibberish? The probe should be 30.8mm(1.21') long, and should be set 63mm (2.5') from the inside of theback lid of the can. The operating wavelength of 4.8' shows us thatwe don't have to worry that the sides of the can have ridges, because the theirdepth is insignificant compared to the wavelength our signal. The GuideWavelength is the wavelength of our waveguide. The TE11/TM01 Cutoff frequenciesgive us the approximate upper/lower frequencies of operation for our antenna.Since Channel 1 is centered at 2412MHz and Channel 11 is centered at 2462 MHz,we have a comfortable margin. Now the interesting part is that if you wanted totune the waveguide for the center frequency of Channel 1, you would use a probedistance of 66.04mm instead, and for Channel 11, you would use 58.52mm. Whatthis means is that there is a whopping 5.48mm difference in the optimal probedistance between Channels 1 and 11, so if you are going to use the antenna on afixed channel, it's better to enter than channel number instead when running theprogram.

Experimenting with my calculator program, I've found some interestinginformation. As the waveguide diameter increases, the difference in optimalposition for the driven element between Channels 1-11 drops. I triedupping the diameter iteratively until the TM01 cutoff frequency started to gotoo low to do Channel 11. From my studies, it seems that about 92mm is theoptimal diameter for the waveguide if you want to try to optimize it forflattest response across Channels 1-11; this is because it minimizes thedifference in the probe position between Channels 1-11 -> about 2.63mm, sothe SWR curve across the WiFi band is flatter.
Contrary to popular belief on the Internet, a can length of 3/4 the waveguidewavelength is not optimal. The ARRL Antenna bookrecommends 2-3 waveguide wavelengths instead. I've found that adding more cansindeed increases the gain. A 4-can one is the longest I tried; I didn't writedown the gain testing results, but it was considerably better than the 1-canantenna. Adding more cans helps launch the standing waves in the can better. bmoore314has some excellent info in this Netstumbler.comthread, including info about adding a conical collector to it. Myresults from experimenting with a conical collector are documented in thesection about my Bazooka Cantenna.

Toothpick Monopole

This is my first attempt at designing something myself. I downloaded the EZNECdemo from www.eznec.com and started fiddlingwith it. I still don't have a good grasp of how to model a real ground plane,but i was able to get some plots and start tweaking things.
I started w/ a quarter wave whip. In the US, Channel 6 is the middle channel at2.437GHz. This makes a quarter wavelength about 30.6mm, so I started with thisand just experimented w/ various lengths to change the pattern and SWR and endedup with 89mm. EZNEC shows SWR of 1.2-1.6 over the WiFi band and gain of 4.35dBmax assuming a perfect ground (which we don't have). Below are plots of my EZNECmodel:

Here is my prototype:
It's just a piece of 2mm dia. coat hanger cut to 87mm and soldered into anN-female panel jack for 89mm length from the tip to the base of the middle pinon the jack. Just for the hell of it I soldered on the ground plane, which isthe lid of a 3.25' dia. tin can. The tape is just to keep me from shreddingmy fingers on the sharp edges. How well does it work? I was amazed. walkingoutside with MiniStumbler, i can find my AP 120ft farther away than with theORiNOCO built in antenna. Inside the house, I went the the place w/ the worstreception and the signal & SNR went up by over 10dB vs the built in antenna.I haven't even begun to tweak the thing yet. not bad for a $4 antenna (the costof the N jack).

Comtelco 7.5dBi Patch Antenna Clone

This antenna has a pageof its own.

Mobile Mark 5dBi Ommi Clone

The Mobile Mark 5dBiantenna is the stumbling antenna of choice used by many Netstumblers. outcast_onewas kind enough to post some pictures on the Netstumber.com website which wereclear enough to get measurements from. Hope he doesn't mind my re-posting themhere:
From the above photos, I estimated the dimensions below:

wire: ~1.5mm OD
ground plane to coils: 34mm (9.5mm of that is under the black plastic bump..wonder what's in there?)
length of coils: 13mm
coil ID: 5mm
coil OD: 7mm
coil spacing: ~3-3.5mm
coils to top: 51.5mm+13mm(plastic tip)..wonder how high the wire goes into the tip.

Here is my implemenation alongside my toothpick for comparison:
I used solid copper wire cut out of a piece of Romex...I forget the gauge..itwas all I had available; tried initially to bend a coat hanger but the steelwire was too difficult to bend into the coils. Once again I used a 3.25'can lid as the ground plane; this is close enough to Mobile Mark's specified3' ground plane. A nicer implementation would be to use a discarded harddisk platter (kudos to sparafina for that idea). I am worried that thecopper is too soft to stand up to high winds when attached to my car. When I geta chance I will either encase the whole whip on a plastic tube or just supportthe coil by inserting a suitable piece of plastic into it. Another idea is tojust fill the coil with hot glue.
My initial tests were not that promising...the gain was about the same as mytoothpick, except that the antenna seemed less sensitive to polarization.However, stumbling with the antenna has shown that on the average, I pick upAP's 1-2 car lengths farther away than with the toothpick, and the SNR is oftena little higher. Therefore, this antenna is used in my current stumbling rig.

Trevor Marshall's BiQuad

Trevor Marshall has posted plans, as well as NEC2 models for his biquaddish feed. The antenna can also be used standalone.
I fashioned the reflector from a discarded tin can. The reflector is 123x123mm,with 30mm 'lips' as specified by Trevor for standalone use. The drivenelement is composed of copper wire I got out of a piece of Romex, with 30.5mmlegs, and is suspended 15mm above the reflector. The antenna as pictured above wasa complete failure and had horrible performance. Trevor explained tome via e-mail that I messed up the feed (the photos on Trevor's site aregrainy). Here is my revised feed:

Instead of rigid coax as specified by Trevor, I just used some more copper wirefor the connections; I'm not sure how this affects VSWR, but the antenna gave meabout 3dB more gain than my Comtelco patch clone during my initial tests.

Bazooka Cantenna

I've been trying to hook up my brother, who is a professor at a local college tohis campus network. He lives just on the edge of campus, and although the ITDept. has discussed putting an AP on his side of the street, no progress hasbeen made for several months. Therefore, I decided to take matters into my ownhands. There are tons of AP's just around the corner and out of LOS from mybro's house, but his block is strangely completely devoid of any signal.
Finally, one day I climbed up on his roof to see if I could get LOS and a signalfrom a yagi on a hill which was pointed away from my brother's house. I used myORiNOCO card in my Jornada, pointed my biquad through a tree, and amazingly gota 5dB SNR! Now we were in business, but the 5dB seemed a little too weak forreliable communications, especially with the chance of the tree growing denserfoliage.
I decided a cantenna might be the way to go, so I built a new one using 33.25' diameter cans...this makes the total length about 1.75 waveguidewavelengths. The driven element is 30.75mm long and mounted the 64mm from theback of the can. The conical collector is 7.25' in diameter on the bigside, w/ a 30degree flare. This was just a quick prototype so I made thecollector out of 2 coat-hanger circles, separated w/ four 4' long coathanger supports covered in aluminum foil. the final design will need to be moredurable to stand up against wind & hail. Here is what it looks like:
Before trying it on the target site, I did some testing with my AP at home. Hereare the SNR's I got across the street from my AP:
ORiNOCO built in: 26 dB
2 cans w/o collector: 36 dB
3 cans w/o collector: 37-38 dB
Trevor Marshall biquad: 39 dB
3 cans w/ collector: 43 dB (!)
This is the highest gain antenna I've built yet. In my excitement, I dragged myJornada off a table while connected to this %$* thing and it fell on the floor.Lucky the card & Jornada are ok, but I broke off the end of my pigtail.
The next morning, I climbed on my bro's roof armed w/ the bazooka cantenna.Going back to the same place I got the 5dB SNR w/ the biquad, the bazooka got8dB. I fired up PocketIE on the Jornada, and was able to surf a little -paydirt! Since it was daylight this time, I was able to try out more places onthe roof, and finally found one clear of the tree which yielded 12dB SNR. Nowwe're in business; I've got a little more margin to play with so when I hook upthe long LMR-400 cable to get the signal inside the house I won't get killed byattenuation.
To be continued after I get the rest of the equipment to complete thesetup...

Biquad Antenna Design

In the meantime, I played with the bazooka from the deck of my hillside house,and was astonished to find that it picked up an AP I'd detected while stumblingon the freeway in my car (using my Mobile Mark clone on the dash). Plugging theGPS coordinates in from the freeway into Microsoft Streets & Trips, it turnsout the AP is about 4 miles away! Using the bazooka on at my house, the SNR was8dB (signal ~-88dBm). As a comparison, I also tried the biquad. Using thebiquad, the signal is unstable w/ max 4dB SNR, and it catches the AP for only asecond at time.

Collinear Omni

This antenna has apage of its own.