[WLAN] Double Biquad Antenna 13dBi

[NanoSoftTech]

 Double Biquad Antenna

This page contains details on building a double biquad antenna with approx 13dBi gain.

Background
Having experimented with a number of biquad antennas (construction details here), I have found them to be relatively easy to contruct, reliable, and good performers, with about 11 dBi gain.

A number of websites showed a variation of the biquad, with the reflector being double the size, and with the element having twice as many sections.

I decided to make a double biquad, to see how the gain compared to that of a biquad.

Construction
I made a double biquad using exactly the same construction techniques as described on my Biquad Antenna Construction page, except the rear reflector is 110x220mm, and the element is double the size.



double biquad

Note that the element wires do not touch where they cross over, but are separated with a gap of approx 1-2mm.

To provide some more robustness, and to ensure the element doesn't move, I added some spaces at each end of the element.
The spacers are made from a small section cut from a hollow reticulation riser, and attached to the reflector and element using a small wire tie. Measure and cut the spacers to be 14.5mm long, as this should result in the element being the correct 15mm from the reflector.



parts required for the spacers

Drill two small holes in the reflector, in line with each end of the element. The holes must be large enough to allow the wire tie to pass through them.



two holes in the reflector for the cable tie

The spacers are attached by passing the wire tie through one of the holes in the reflector, through the tube, looped around the element, and then passed through the tube again, and through the other hole in the reflector.



spacer installed

The spacers will ensure the posititioning of the element relative to the reflector will not change, and also means the antenna is less likely to be damaged while in transit or while being handled.



detail of spacer

Note that you can make spacers out of any non-metallic material, providing it does not absorb microwaves.

As with the biquad antenna, if you intend to use one of these outdoors, I'd recommend you place it into a weather-proof enclosure, to prevent corrosion, and to prevent water ingress into the coax.



completed double biquad

Testing
To determine the difference in gain between a biquad and the double biquad, some tests were performed, with the signal, noise and SNR recorded.

antenna

SNR(dB)

signal(dBm)

noise(dBm)
biquad	43	-58	-101
double biquad	45	-56	-101

The test results indicate that the gain of the double biquad is approx 2dBi higher than that of the biquad, which is a significant improvement (as 3dBi is a doubling of signal).

As the biquad has a gain of 11-12dBi, this means the double biquad has a gain of 13-14dBi, so it's a pretty good performer for something that's relatively easy to build.

These results are similar to those obtained by other people who have made double biquads.

References
Biquad Antenna Construction
Photos of a Double BiQuad
Double Double Quad
 
 

http://martybugs.net/wireless/biquad/double.cgi

[NanoSoftTech]

WLAN 802.11b/g Bi-quad antenna: building and testingReport on reproducing Trevor Marshall's BiQuad Antenna.Antenna specifications: 11dBi, wide band
For original article see: http://trevormarshall.com/biquad.htm
Antenna wire: lenght 244 mm, diameter 1.2 mm, aluminium
Reflector: circuitboard 123 x 123 mm
Cable: N-female 300mm test-cable MIL-STD RG-58C (semi-rigid)




Complete antenna.
Notes on building:
The center frequency is very sensitive to how you solder the ends ofthe quad loops to the coax. After multiple attempts it was determinedthat even a half a millimeter difference will move the center frequencyby as much as 50 MHz. So be prepared for a lot of "measure, resolder,measure, resolder ..."
The feedpoint:
one branch of quad to coax center conductor, and the other to the shield (ground).

The feedpoint is the most ‘ugly’ place in the antenna. Try tokeep the gap as short as practicable and the crossing lines together insymmetry - however be prepared to resolder a couple of times to findthe best configuration. Note that, to allow for a gap between thefeedpoint, the ‘quad-ring’ will be distorted somewhat - however try tokeep the quad overall lenght the same 244mm.
When you measure the returnloss/SWR and find that the centerfrequency is off where you want it, you have to make the quad-ring 1mmshorter or longer by adjusting how you solder the quad ends to thecoax. If you find that the returnloss/SWR figure isn't 'sharp' or isdistorted then you probably have some non-symmetry at the feedpoint.

Spot on:
Note that the SWR at center frequency isn'tactually as important as on the channels 1 and 11. You want to centerto be where it dips those frequencies the most.
Test report:
Equipment:

• Spectrum Analyser, 3GHz, IFR 2399B
• Return Loss Bridge, >40dB 3GHz, Eagle RLB150N5A
• Test cables and adapter, 0-18GHz, Rosenberger

Test conditions:
The analyser's tracking generator andseparate return loss brigde were used to test the return loss from thetest port without the antenna attached. This level was set as zeroreference for the measurement markers. The antenna was suspended withcardboard 1 meter above ground with a minimum of 5 meters to adjacentwalls and the ceiling. The antenna was moved around to average outreflections and other anomalies caused by the less than perfectmeasuring conditions.
Results:
Marker 1: 2412 MHz (Channel  1), Return loss -23dB = SWR 1.2
Marker 2: 2437 MHz (Channel  6), Return loss -33dB = SWR 1.1
Marker 3: 2462 MHz (Channel 11), Return loss -23dB = SWR 1.2

Notes on measuring:
No, you don't need a billiondollar network analyser to do antenna measurements. Very good resultscan be achieved with a ordinary spectrum analyser with trackinggenerator option. All you need is a good quality return loss bridge andsome test cables and adapters. At 2.4GHz your equipment needs to berated for atleast 3GHz operation and the cables and adapters must havelow loss and good SWR at these frequencies. Using poor cables oradapters in reflection measurements will give you 'better' results thanreality would warrant. Remember that in reflection loss measurementsyou are measuring the reflected energy from the antenna, which at goodSWRs will be very small fraction of the tracking generators output.
Here's a small table for converting reflection loss and SWR:For example if the reflection loss is -20dB this means 1% of the energytransmitter is reflected back. This is equivalent to an SWR of 1,222which is very good.

Ref dB	SWR	Ref Coff.	^ -1		Ref dB	SWR	Ref Coff.	^ -1
-1	17,391	0,7943	1,26		-21	1,196	0,0079	125,89
-2	8,724	0,6310	1,58		-22	1,173	0,0063	158,49
-3	5,848	0,5012	2,00		-23	1,152	0,0050	199,53
-4	4,419	0,3981	2,51		-24	1,135	0,0040	251,19
-5	3,570	0,3162	3,16		-25	1,119	0,0032	316,23
-6	3,010	0,2512	3,98		-26	1,106	0,0025	398,11
-7	2,615	0,1995	5,01		-27	1,094	0,0020	501,19
-8	2,323	0,1585	6,31		-28	1,083	0,0016	630,96
-9	2,100	0,1259	7,94		-29	1,074	0,0013	794,33
-10	1,925	0,1000	10,00		-30	1,065	0,0010	1000,00
-11	1,785	0,0794	12,59		-31	1,058	0,0008	1258,93
-12	1,671	0,0631	15,85		-32	1,052	0,0006	1584,89
-13	1,577	0,0501	19,95		-33	1,046	0,0005	1995,26
-14	1,499	0,0398	25,12		-34	1,041	0,0004	2511,89
-15	1,433	0,0316	31,62		-35	1,036	0,0003	3162,28
-16	1,377	0,0251	39,81		-36	1,032	0,0003	3981,07
-17	1,329	0,0200	50,12		-37	1,029	0,0002	5011,87
-18	1,288	0,0158	63,10		-38	1,025	0,0002	6309,57
-19	1,253	0,0126	79,43		-39	1,023	0,0001	7943,28
-20	1,222	0,0100	100,00		-40	1,020	0,0001	10000,00

<!--[if supportMisalignedColumns]--> <!--[endif]-->[/table]
( VSWR = 1-SQRT(Reflected/Forward) : 1+(SQRT(Reflected/Forward) )
Contact:
Miikka Raninen (OH3GPJ), Tampere, Finland

Created on ... June 29, 2006



http://koti.mbnet.fi/zakifani/biquad/

[NanoSoftTech]

Biquad Antenna Construction
(first published September 2002)

This page details the construction of a biquad antenna. The biquad antennais easy to build, and provides a reliable 11dBi gain, with a fairly wide beamwidth.

Contents:

Background | Parts Required | Reflector | Making the Element | Assembly | Testing | Variations | Usage | Kits | References

Background
I've done quite a bit of experimentation and testing with varioushome made dipoles for 24dBi Conifer dishes,and have managed to increase the performance of the dish.

Trevor Marshall has a webpage with informationabout using a biquad as a feed on a Primestar satellite dish, with very goodresults. I decided to try using a biquad as a feed on a 24dBi Conifer dish,to see if I could improve the performance of it of the dish.

Note that the photos on Trevor Marshall's webpagedo not clearly show the construction of the biquad - particularly the wayin which the quad is attached to the coax. Numerous people (including myself)have constructed biquads incorrectly, based on his photos, and found thatthey perform very poorly.
Use the photos of my biquad below, and refer to the websites listed in thereferences section at the bottom of this pagefor more information on the correct construction of the biquad.


Parts Required
I used the following bits and pieces:

• 123x123mm square section of blank PCB
• 50mm length of 1/2" copper pipe
• short length of CNT-400 or LMR-400 low loss coax (~300mm long)
• 250mm of 2.5mm² copper wire (approx 1.5mm diameter)
  
• N connector

Note that you don't have to use blank PCB for the reflector. You can use any materialthat's electrically conductive, can be electrically connected to the coax braid,and will reflect microwaves (ie, any metal plate will do fine).
I've also heard of people using CDROM as the reflector, as the foil on it will certainlyreflect microwaves.


Reflector
Cut a square piece of blank printed circuit board, 123x123mm.

Note that Trevor Marshallrecommends a size of 123x123mm if using the biquad as a stand-alone antenna,while 110x110 is optimal if using it as a feed for a large dish.
He also recommends attaching some lips to two sides of the reflector, toreduce radiation from the rear lobes.

Use some steel wool to remove any tarnish and polish it up.Cleaning the copper in this way will make it easier to solder.



blank printed circuit board
Cut a 50mm section of copper pipe, and file both ends smooth.Using some sandpaper and/or some files, polish up the copper pipe (including the inside of the copper pipe, to ensure a good connection withthe coax braid).



the dimensions of the copper pipe
Cut a notch into one end of the copper pipe, removing approx 2mm from half the circumference.



a short secion of copper pipe, notched at one end
Drill a hole in the centre of the blank PCB so that the copper pipeis a tight fit in the hole. I found a reamer to be very useful forenlarging the hole to the correct size.



making a hole in the centre
Insert the copper pipe into the hole, with the notched end on the copperside of the blank PCB. The copper pipe should be protruding approx 16mmthrough the hole, measured on the copper side of the PCB.



insert the copper pipe into the reflector
Solder the copper pipe to the PCB, to ensure a good physical and electrical connection.



solder the copper pipe to the PCB
Quite a bit of heat is needed, due to the thickness of thecopper pipe, and an electrical soldering iron probably won't be able todeliver sufficent heat. I found a small gas torch works quite well.



Making the Element
The element is made from a length of copper wire, bent into the appropriate shape.

Note that the length of each "side" should be as close to 30.5mm as possible (measuredfrom the centre of the copper wire to the centre of the copper wire), which isa quarter of a wavelength at 2.4GHz



the shape and dimensions of the element
I had some offcuts of electrical power cable lying around, and found that 2.5mm² power cablehad a diameter of approx 1.6mm - a little bigger than the 1.2mm that Trevor Marshallspecifies, but didn't think it would make a significant difference to the performanceof the biquad.



recycling power cable offcuts
Remove the insulation, measure and cut a 244mm length the copper wire, and straightenit as best as you can.



straighten the wire
Measure the mid-point of the wire, and make a 90 degree bend. The bend should bequite sharp and pronounced.



90 degree bend
Measure the midpoints of each half, and make two more 90 degree bends in the wire,so that it looks like that shown in the photo below.



another two bends
Once again, measure the midpoints of each section, and make some more 90 degree bends,resulting in what is shown below.



bend it some more...
Do the same to the other side, resulting in the biquad shape.



make it symetrical...
Clean up all your bends, and ensure each side of the element is as straight as possible,and as close to 30.5mm as possible.
Note that you may need to trim a small amount off each end of the wire to achieve this.


Assembly
The element must now be attached to the reflector. Note that only thetwo "ends" of the copper wire are to be attached to the copper pipe - the centre of the copper wire must not touch the copper pipe (hence the notch which was cut into the end of the copper pipe.

The copper wire element should be approximately 15mm away from the reflector.Testing antenna performance while varying the spacing between the copper wire elementand the rear reflector indicates that a spacing of approx 15mm provides the lowest SWR(test results available here).



the element soldered onto the copper pipe
Strip approx 30mm of the outer sheath from the end of the coax.



strip the outer sheath
Fold the braid back over the outer sheath, and trim the centre conductor,so that about 4mm is protruding.



fold the braid back, trim the centre conductor
Insert the braid into the copper pipe, so that the end of the centre conductor lines up with the extreme end of the copper pipe, and solder the centre of the elementto it, ensuring the centre of the element is not in contact with the copper pipe.Refer to some of the additional photos below for details.



solder the centre conductor to the element


another view
Note that the feed between the rear reflector and the biquad elementneeds to be shielded. Using coax to feed the biquad element directly,and positioning the coax inside the copper tube achieves this.
Use of bare conductors as a feed between the reflector and biquad elementresults in a radiating feed (such asthis one), which will have a detrimental effect on the biquad's performance.

I used a coax crimper to crimp the end of the copper pipe onto the coax.This ensures that the coax would not move inside the copper pipe.



the copper pipe crimped onto the coax


the completed biquad
Now terminate the other end of the coax with an N connector.

If desired, you can add spacers at each end of the element, to ensurethe element doesn't move in relation to the reflector.Refer to my double biquad page for more detailson making spacers to support the element.

If you intend to mount the biquad outside, I'd recommend you place it into aweather-proof enclosure, to prevent corrosion, and to prevent water ingress into the coax.
Numerous people have used small tuppaware containerssuccessfully.

This can be achieved by drilling a hole in one side of the container, and pass the coax tail through the hole, leaving the biquad itself inside the container. Seal up the hole for the coax with some silicone, and yourbiquad should be protected against the elements.



another view of the completed biquad

Testing
Some very rough initial testing using the biquad as a feed on a 24dBi Coniferdish looks very promising, with the signal strength being at least as as goodas my home made Conifer dipole (I was holdingthe biquad at approximately the focal point of the dish, and hadn't even removed the Conifer dipole).

I also managed to get a marginal link to a 180 degree waveguide on an access point 10km away, using only the biquad by itself, connected to a 30mW RoamAbout wireless card.

Some more detailed testing with multiple antennas,including the biquad shown above, indicates the biquad has a gain of approx 11-12dBi.

A friend has access to some antenna test equipment, and performed some testson the biquad featured on this page.
The azimuth plot (ie, radiation pattern) of the biquad is shown below, and shows a 3dB beamwidth of about 50 degrees.



azimuth plot of the biquad

Variations
A number of people have suggested the spacing between the element and the rearreflector should be a 1/4 wavelength (ie, 30.5mm) instead of 15mm.However, test results(such as these)indicate the SWR of the biquad is minimised when the spacing is about 15-17mm. Increasing the spacing to 30.5mm increases the SWR significantly, thus reducing the efficiency of the biquad.

For a higher-gain variation of the biquad that's virtually just as easy to build, have a look at the double biquad.


Usage
When using a biquad to establish a link to another wireless device, youshould ensure the polarisation of the biquad is the same as the antenna you areconnecting to. Similarily, if establishing a link with two biquads,ensure they are both oriented for the same polarisation.
Failing to match the polarisation will result in significant signal loss.

vertically polarised

horizontally polarised

Changing the polarisation is just a matter of rotating the entire biquad antenna by 90 degrees.

The biquad antenna is not particularly directional, but has a fairly wide beamwidth.
The 3dB beamwidth for a biquad (without side lips) is typically about 40-50 degrees,thus making it ideal for any applications where you want fairly wide coverage.

The relatively wide beamwidth also makes a biquad very suitable for war-drivingand stumbling, allowing you to pick up signals without having to align the antenna directlywith the signal source.

While a directional antenna, such as a Conifer dish(3dB beamwidth of a 24dBi Conifer dish is approx 7 degrees), is better suited for point-to-point links, the narrow beamwidth of a Conifer dish requires moreprecision when aligning the antennas (the narrower the beamwidth,the less susceptible it will be to interferance from other sources).An antenna with a wider beamwidth, such as a biquad, doesn't require the sameprecision for alignment, thus making it easier to get a link working.


Kits
If you're one of those people who may not have all the tools required for building a biquadantenna from scratch, or you don't want to shop around for all the parts required, you can buy a DIY kit containing all components fromWarDrivingWorld.

In November 2006, WarDrivingWorld sent me one of their DIY biquad kits to review. The kit contains all the pre-cut and pre-drilled parts required to build a biquad antenna.
For more infomation on this kit, including antenna comparision test results, read myReview of the WarDrivingWorld DIY Biquad Kit.


References
Trevor Marshall's BiQuad 802.11b Antenna
Simple Double-Quad Antenna
Reseau Citoyen: BiQuad
Lincomatic's Homebrew WiFi Antennae


http://martybugs.net/wireless/biquad/

[NanoSoftTech]

How-To: Build a WiFi biquad dish antenna
by Eliot Phillips, posted Nov 15th 2005 at 2:45PM
<!-- sphereit start -->

Wireless enthusiasts have been repurposing satellite dishes for acouple years now. This summer the longest link ever was established over 125 milesusing old 12 foot and 10 foot satellite dishes. A dish that big isusually overkill for most people and modern mini-dishes work just aswell. The dish helps focus the radio waves onto a directional antennafeed. We're building a biquad antenna feed because it offers very goodperformance and is pretty forgiving when it comes to assembly errors.Follow along as we assemble the feed, attach it to a DirecTV dish andtest out its performance.
Why? With just a handful of cheap parts, a salvaged DirecTV dish anda little soldering, we were able to detect access points from over 8miles away. Using consumer WiFi gear we picked up over 18 APs in anarea with only 1 house per square mile.
Building the antenna
Biquad antennas can be built from common materials, which is nice because you don't have to scrounge around for the perfectly-sized soup can. We did have to buy some specialized parts before getting started though.

The most important part here is the small silver panel mountN-connector in the center of the picture; the entire antenna will bebuilt on this. We purchased it from S.M. Electronics, part# 1113-000-N331-011.The "N-connector" is standard across the majority of commercialantennas and you can connect them to your wireless devices using"pigtails." The longer pigtail in the picture is a RP-TNC to N-Male pigtail that we'll use to connect our antenna to a Linksys WRT54G access point. The short pigtail is a RP-MMCX to N-Male pigtail so we can connect to our Senao 2511CD PLUS EXT2 WiFi card which is pictured. We also purchased 10 feet of WBC 400 coax cable so we wouldn't have to sit with the dish in our lap. We got our surplus DirecTV dish from Freecycle. We'll cover the reason for the mini butane torch later.
Trevor Marshall built one of the first biquad WiFi antennas found on the internet. We followed the slightly more thorough instructions found at martybugs.net. Here are the raw materials we started with:

The wire is standard solid-core 3-conductor wire used for most housewiring. We didn't have any copper printed circuit board material layingaround so we used this thin sheet of copper and supported it using the1/4-inch thick black plastic pictured.
The first step in building the element was stripping and cutting a 244mm length of wire.

We marked the wire every 31mm with a permanent marker and beganbending the wire into a double diamond shape. We tried to make thelength of each leg 30.5mm.

The easiest way to make really sharp bends in the solid copper wireis to use two pairs of pliers. With the pliers held perpendicular toeach other bend the wire against one of the sets of jaws.

The element with all bends completed:

Next we cut out a 110mm square of black plastic to use as a base forthe reflector. We drilled a hole in the center to clear our connector.

We then soldered a piece of copper wire to the center pin of our N-connector.

Next we soldered a piece of of wire to the outside of the connector. Weran into some trouble here. Our cheapy iron was not capable of gettingthe connector's base hot enough to make a good solder joint. We boughta butane torch and used that to heat up the surfaces. This workedpretty well except it desoldered our center pin. We recommend yousolder the outside piece of wire first before doing the center one.

After the connector had cooled it was attached to the black plasticbase using epoxy. The thin copper sheet was attached to the front withepoxy and trimmed to fit.
We let the epoxy cure for a while before proceeding. The next stepwas to solder our bow tie shaped element to the vertical wires. Theelement was supported by two pieces of scrap copper trimmed to 15mm toensure proper positioning.

Then the extra wire was trimmed off and the outside wire was soldered to the ground plane to complete the antenna.

To make mounting to the dish easy we modified the original feedhorn. Here is what it originally looked like.

After removing the housing, internal components and shortening the feedhorn looked like this.

The antenna is attached by inserting the N-connector into the tube and then connecting the coax cable.

Here is a picture of the final antenna assembly ready to be attached to the dish.

Since the satellite dish has an off-center feed it looks like it ispointed at the ground when it is level with the horizon. Even thoughthere are no angle markings for setting the dish at 0 degreesinclination we can still ensure that the dish is pointing at thehorizon by setting the dish angle to 45 degrees and mounting it on atube with a 45 degree angle.

Test results
The Engadget Corn Belt Testing Facility has broadband accessprovided by a local WISP. So we knew if we plugged in our antenna wewere sure to pick up something in the area. We pointed the dish at theclosest grain elevator, where the WISP mounts their antennas. Weconnected the dish feed to our Senao card and started up Kismet.

We expected to get one AP, but five is even better. Looking throughthe info strings we were able to determine where the APs were since theWISP had named them according to the town they are in. The AP onchannel 5 is the one we pointed at in town A, 2.4 miles away. The AP onchannel 6 is located in town B, 8.2 miles away. The two APs on channel1 are a bridge between town A and town C which is located 2.6 milesdirectly behind the dish.
Our next test was to hook our WRT54G up to the dish and point it ata hill 1 mile away. We drove to the top of the hill and used an omnidirectional mini whip antenna with our Senao card to detect it.

Our router was picked up easily. The found 14 other WISP APsincluding town D, 7.8 miles away. The WISP is definitely using somehigh powered equipment if we're just picking this up with anomnidirectional antenna.
For a final test we put the dish on the roof rack and parked on top of the hill to see if we could pick up any more APs.

Our final count is 18 APs, 17 of those belonging to the WISP. Thiswas a pretty fun project and shows that you can build decent wirelesssolutions using consumer gear.
For the curious: The WISP gives its subscribers a patch antenna witha built in power-over-ethernet access point. Once the antenna ismounted to the roof they run a single ethernet cable into the housewhich means they don't have to worry about signal loss from coax. Theseclient boxes are manufactured by Tranzeo.



http://www.engadget.com/2005/11/15/how-to-build-a-wifi-biquad-dish-antenna/

[NanoSoftTech]

Trevor MarshallBiQuad 802.11b Antenna11dBi, wide band

***Watch SeattleWireless TV's Eric Hall describe how to assemble a BiQuad * ***
Miikka Raninen (OH3GPJ) builds and tests the biquad
Click here for details of Mark LaPierre's 1100ft link through forest canopy, and comparison with Pringles can performance.
Click here to link to Koen Weijand's page on using an 18inch dish and feed details
Link to my tutorial 'Antennas Enhance WLAN Security' from BYTE.com, October, 2001
Click here to read about the High Gain(15-17dBi) Slotted Waveguide WLAN antennas

Low sidelobe 802.11b BiQuad feed for Primestar dish The Primestar dishes are high gain, low cost, parabolic reflectors withan offset feed. They have superior sidelobe performance when comparedwith a wire grid antenna, reducing the chance that somebody off of theaxis of your link will be able to interefere with it. But they are hardto feed because the f/d ratio varies from about 0.5 in the verticalaxis to 0.8 on the horizontal axis. Additionallythe spacing between the feed 'slot' and the feed mounting bar is small(about 55 mm), which is less than a half wavelength at 2.4GHz Failureto couple efficiently to the dish's wide aperture, or to minimizeradiation into the mounting bar, will result in poor gain and/orsignificant sidelobes. The feed is oriented for verticalpolarization in this photo. To make it horizontal merely rotate thefeed by 90 degrees. You will lose about 3dB of gain when using thehorizontal mode, as the biquad's radiation pattern is a better matchfor the dish's oblong shape when vertical polarization is used.

Construction of the Biquad I used Printed Circuit board scraps for the 110 x 110 mm reflector, butit will be just as effective if made out of sheet brass or copper.Aluminum can be used if soldering of the rigid coax is not required atthe feed point. Thereflector's 'lips' are 30 mm high, and serve to reduce coupling intothe mounting bar. Note that they are only required along the main edgeaxis of the reflector. The lips cut down radiation from the rear lobesof the biquad by about 6 dB The best SWR is obtained when thebiquad loop is about 15mm above the ground plane, and the SWR may beadjusted by varying this distance. If you are making a stand-alone antenna, rather than a feed, you will get better gain from a reflector 123 x 123 mm

A piece of 3/4 inch copper piping makes a tight fit with the mount supplied on the Primestar dish The rigid 0.141 diameter coax is soldered to the groundplane to providephysical support for the structure. If the biquad element isconstructed carefully there will be no component of radiation along theaxis of the coax, no current is induced into the coax outer conductor,and a balun is not needed. An SMA connector can be seen on the end of the rigid coax used to support the biquad element

To make the element take a piece of 1.2mm bare or enamelled copperwire exactly 244 mm long. Bend it in half, and then make the bends atthe halfway point on each leg (where the solder joints will be). Thenbend the 4 remaining right angles so that the element sides arerectangular, and there is about a 1.5mm gap for soldering to the feed.The widths of the two quad elements will be approximately 30.5mm, fromwire center to wire center. You may use standard coax cable toconnect at this point, if you do not have rigid cable available, butyou will have to figure out how to support the loop physically. Thebest SWR is obtained when the loop is about 15 mm above the groundplane and when the reflector is mounted about 10mm in front of thePrimestar's feed bracket.

That's all there is to it, folks -- you now have a dish with 27-31dBi of gain and negligable sidelobe radiation (<40dB). The beamwidthis about 4 degrees.
 

Look at NEC2.org for information on simulating the performance of the stand-alone Biquad
BiQuad Antenna for PCS CELLULAR Radio
Need a little bit more range for your cellphone? You can make a Biquadfor 1900 MHz exactly the same as the one above, but start with a 304 mmlong pice of wire, fold it into 8 arms approximately 39.5 and 38.5 mmlong. The ground plane needs to be a little larger, use one about 160mm (6.2 inches) square. If you don't have a coaxial RF input jack onyour cellphone you can couple the signal into its existing antennausing a single quad as a matching stub. It's not perfect, but inpractice it works well. Solder an alligator clip to either of the highvoltage apex (39mm from the feed) of a single 152 mm loop, and clipthat to the antenna stub you are currently using. Now you can put 100ft of coax between your phone and use a roof antenna (the BiQuad) tooperate even in fringe areas.
 
Link to my article 'Antennas Enhance WLAN Security' in BYTE.com, October, 2001


http://www.trevormarshall.com/biquad.htm

[NanoSoftTech]

[SIZE=+1]Building a biquadantenna for wireless 802.11b
  [/SIZE]      
Wireless 802.11b are becoming very popular these days, so arethe art of extending the range of such devices. Most people when beginto know what is wireless networking and that it uses antennas to extendits range thougth on that old parabolic dish they used to watch TV.Surely it's posible to use it for 2.4Ghz that is what 802.11b standarduses.
 
This is not a new design it's only the way we build theantenna, our source of information is Tevor Marshall websiteso, go there for more detailed description.
We get the materials that we have at home to do it, so it's aparticular antenna.
 
 
N female panel type connector .
110mmx110mm aluminum plate it's 2mm thick.
Piece of 1.2mm bare or enamelled copper wire 244 mm long.
A parabolic dish as big as you can found.
 
 
Where do we found these materials?
- Plate was cutted of an old 28800 external modem.
- Copper wire it's from inside an PC AT power supply.
- N connector, we bought it.
- Parabolic dish, we found it beside a trash container, it's diameteris about 660mm
 
 
Tools used:
clinch tool.
solder.
pliers.
 
 

 
This piece of aluminium it's: 110x110 mm with a hole in the middle forthe N connector.
 
 
 
Bend the wire to give it this form.
 
 
 
We used a N panel female connector.
 
 
 
The hard work was to solder the wire to the outer side of the Nconnector, we used sand paper.
 
 
 
Now it's assembled, note that the N connector is only attached withtape (by now).
 
 
 
A side view.
 
 
 
 

This is a test, the biquad and aparabolic dish, we managed to connect to the pinedawireless node that wasabout 3 km away, it was tricky to position the biquad and the dish totarget it rigth.
If you ask me how many db is this biquad antena, I don't know but morethan 20db (I think so)
 
 

   
 
 

   



http://www.sorgonet.com/network/biquad/

 

[NanoSoftTech]

How to make a 802.11b BiQuad Antenna for WiFiA practical guideIn october of 2002 Marten Vijn (WirelessLeiden) gave us a clear, practical workshop on making bi-quads. It was possible to make this page thanks to his vast experience on this subject.
Bi-quads are simple directional antennas for use in 2.4 Ghz radio connections, mostly wireless networks or WiFi.
This type of antenna can be easily built. Exact size and constructionare not very critical. They almost always work. Their typical gain is8-10 dBi, which is pretty good. They look like this:

The antenna is built on a piece of Printed Circuit board of 10 by 15 centimeters. Right in the middle of this we drill a hole that is the size of the diameter of a female N-connector chassis mount.


The female N-connector chassis mount:

The heart of the antenna is a piece of bended brass or copper wire

The diameter of the brass or copper wire should be about 1.5 millimeter. The inner sides of the squares (quads) must have a size of about 28 mm. A tolerance of a millimeter or so is allowed.
The following link shows a drawing with an overview of various measures: wleiden.webweaving.org/bq.pdf  (Text is in dutch)
Thebending of the wire is the hardest. It is important to have the finalbended wire in one plane. This can be checked by laying the copperproduct on a flat surface. All the copper should be stable and flat onthe surface. It should not wobble.
Marten constructed a special little tool too make the bending easier.

But with a pair of tongs it can be done too.

After the copper has been bended right it is soldered on the chassis mount:
The distance between the PCB and the copper wire must be about 15-17 millimeters. With the chassis mount shown here this distance can be adjusted. In other types it must be soldered rather precisely.

The two end points of the bended wire are connected with solder and connected to the chassis mount. Right at other side of the copper - where the wire makes an inside angle - is the other connection point with the chassis mount.This can be seen on the next picture:

There is no plus or minus. It does not matter what is connented to the middle of the chasis mount.The soldering can best be done with a solder pistol or a pretty powerfull soldering bolt (50-100 VA). My 25 VA soldering bolt did not do the job. On the other hand care should be taken not to make the chassis mount too hot, the kernel can melt and be damaged
The result should now be as already shown above:

The antenna is now ready for use.
It is advised to put the result in a box of some kind, especially when it's used in outside weather conditions. Microwave boxes as used by take away food stores are fine. The same is true for plastic boxes for video tapes, these are just the right size.Boxes should not contain any metal or absorb water.This can be tested by laying them in a microwave for a minute or so. If the do not become warm it's ok. If they do get hot, considerable loss in gain may be the result.
Good luck.
Tom Duijkers

Leiden, The Netherlands.




http://www.xs4all.nl/~tom1572/eng/index.htm

[NanoSoftTech]

Biquad Sector antenna for 2.4 GHz  / 802.11b / WiFi / WLAN
D.R.O.I.D Reality isn't everything
Latest version of this document can be found at http://flakey.info/antenna/biquad/index.xhtml
Last updated - 18th February 2004 | Flakey.info
Overview
This sector antenna was made from a piece of thick copper wire formed into a "bowtie" shape (the biquad - with sides 32 millimetres)  and soldered to a round N-type connector. The N connector was then screwed into a steel disc about the size of a CD (Compact Disc).
The original prototype (shown) is still in use two years later, and has survived severe storms.


Note - This antenna is for use with 802.11b wireless computer networks or 2.4GHz video sending equipment. It is not for FM / AM / SW / LW radio useage.

A semi-technical diagram of the biquad antenna

Construction


   
The connector - N-type


   

N-type socket round "through bulkhead" came from R.S. number 112-0773. Packaging says Telegartner (Manufacturer presumably) Type N-Einbaubuchse J01021A1084 Tel +49 (0) 7157/125-0 Fax -120


   
The biquad ("bow-tie" bit)


   

The "bowtie" section was made from a length of copper at least 400 mm (0.4 metre) long. The wire came from standard twin-and-earth stiff household mains wiring. By holding either end of the wire with a pair of pliers and giving it a sharp tug the wire was straightened. Leaving about 20 mm before starting, the bowtie shape was folded into the wire using the pliers, with the side of each square being 32 mm. The edge of the pliers was useful to obtain right angles. Both ends of the wire end up in the same place once the "bowtie" is formed. These were soldered together and bent 90 degrees out of the plane of the bowtie, ready to be soldered to the casing of the N-type connector. The "bowtie" then had an extending piece of wire soldered to it at the point where there is a 90 degree bend joining the two squares together, ready to be soldered to the centre pin (solder bucket) of the N-type connector.


   
Soldering


   

We worked out where the rear disc (groundplane) would sit when the N-type connector was affixed to it, and then both extending wires we cut so as to stand the "bowtie" off the back plate by 18 mm. The centre pin was easy to solder because it has been tinned by the manufacturer. Soldering the other extending wire to the casing was not so easy. It required the surface roughing with sandpaper, and then tinning with a lot of heat until the solder flows. Once the casing and the end of the wire extension was tinned soldering was easy, while the connector body was still hot. At this point the dialectric (the white bit around the centre pin) started to go a bit soft. We were careful not to move the pin, and ensure it was straight before it cooled.
   

The "bowtie" and N-type connector assembly, before fitting to the ground plane.
   


   
The ground plane


   

We drew around a compact disc on to a sheet of galvanised steel (about 1 mm thick - but none of use know our steel gauges - think it's 8 gauge) - and marked the centre. We used a pair of tin snips to cut out the circle. Using a 20 mm cone cutter, we drilled a 16 mm hole on the centre of the disc (by putting the 16 mm washer from the N-type connector over the tip of the cutter before drilling the hole stops at exactly the right size. We de-burred the edges of the disc with a fine file.


   
Assembly


   

We screwed the "bowtie" and connector assembly into the hole in the ground plane, tightened it up with two spanners, and then carefully adjusted the "bowtie" wire until the plane of the "bowtie" was nicely parallel to the ground plane.


   

Back to the top


   
Weather proofing


   

We have used no weather proofing on these antennas yet. It needs some kind of plastic cap over the front.

   
   

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Mounting


The antenna mounted on the U-bolt assembly.
   



   

These antennas need aiming. We mounted the antenna on a u bolt assembly using the bottom two bolts only. Thus we drilled two holes in the ground plane at the top. Ensuring the bolts protruded only a nut width, and using 2 nuts behind and 2 nuts in front, secured the ground plane to the lower u-bolt


   

The U-bolt assembly was clamped down hard on the bar, pointing in the required direction.



The antenna mounted on the pole, showing cable tie at the bottom as strain relief for the cable.
   


   

Back to the top


   
Cost


   

£5.50 for the N connector. The wire and steel disk were recycled. The u-bolt mounting assembly was around £3.00


   

Back to the top


   
Warning


   

Apart from the fact it works really well, no-one has yet popped on their lab-coat and done any high-brow tests on this "homebrew twig", and of course manufacturers recommend you don't do anything which they don't recommend, or attach non-proprietary stuff to their stuff. Of course.


   

Back to the top


   
Initial tests

   
   

Initial tests show that the antenna has a beamwidth of roughly 70 degrees in elevation (vertical) and azimuth (horizontal) planes, and 12 dB gain in the signal to noise ration over the pcmcia card.





   
   

http://flakey.info/antenna/biquad/

[NanoSoftTech]

Double Biquad Antenna
This page contains details on building a double biquad antennawith approx 13dBi gain.


Background
Having experimented with a number of biquad antennas(construction details here), I have found them to be relatively easy to contruct, reliable, and good performers, with about 11 dBi gain.

A number of websites showed a variation of the biquad, with the reflector being double the size, and with the element havingtwice as many sections.

I decided to make a double biquad, to see how the gain comparedto that of a biquad.


Construction
I made a double biquad using exactly the same construction techniquesas described on my Biquad Antenna Construction page,except the rear reflector is 110x220mm, and the element is double the size.



double biquad
Note that the element wires do not touch where they cross over, but areseparated with a gap of approx 1-2mm.

To provide some more robustness, and to ensure the element doesn't move,I added some spaces at each end of the element.
The spacers are made from a small section cut from a hollow reticulation riser,and attached to the reflector and element using a small wire tie.Measure and cut the spacers to be 14.5mm long, as this shouldresult in the element being the correct 15mm from the reflector.



parts required for the spacers
Drill two small holes in the reflector, in line with each end of the element.The holes must be large enough to allow the wire tie to pass through them.



two holes in the reflector for the cable tie
The spacers are attached by passing the wire tie through one of the holes in the reflector, through the tube, looped around the element, and then passedthrough the tube again, and through the other hole in the reflector.



spacer installed
The spacers will ensure the posititioning of the element relative to the reflector will not change, and also means the antenna is less likely tobe damaged while in transit or while being handled.



detail of spacer
Note that you can make spacers out of any non-metallic material, providing it does not absorb microwaves.

As with the biquad antenna, if you intend to use one of these outdoors, I'd recommend you place it into a weather-proof enclosure, to preventcorrosion, and to prevent water ingress into the coax.



completed double biquad

Testing
To determine the difference in gain between a biquad and the double biquad,some tests were performed, with the signal, noise and SNR recorded.

antenna	SNR (dB)	signal (dBm)	noise (dBm)
biquad	43	-58	-101
double biquad	45	-56	-101

The test results indicate that the gainof the double biquad is approx 2dBi higher than that of the biquad, which isa significant improvement (as 3dBi is a doubling of signal).

As the biquad has a gain of 11-12dBi, this means the double biquad has a gainof 13-14dBi, so it's a pretty good performer for something that's relatively easy to build.

These results are similar to those obtained by other people who have made double biquads.


References
Biquad Antenna Construction
Photos of a Double BiQuad
Double Double Quad


http://martybugs.net/wireless/biquad/double.cgi