# The "Cantenna" has not 12 dBi!!!

#### Have a question or want to start a discussion? Post it! No Registration Necessary.  Now with pictures!

•  Subject
• Author
• Posted on

The Cantenna can not be have 12 dBi gain. Any Cantenna design, I have
testet, had only a performance from 7 to 8.5 dBi.
I found some Canntenna models (.NEC-files) on internet, which
calculates indeed 12 dBi. But the average gain test, which is almost
not done, shows the error in the design model.
If you check and correct this desing errors, you will get only a
performance of 8 dBi.

It is not true, which the cantenna has 12 dBi! Keep in mind.
Aziz

Re: The "Cantenna" has not 12 dBi!!!

oeguet@gmx.de hath wroth:

Show me.  I do designs and models.

The final gain really depends heavily on the waveguide geometry.  The
typical coffee can will do about 9dBi.  Pringles cans are about 7dBi.
Extra long extensions with horns can be as high as 14dBi.

I show 8.5 to 9.8 dBi gain:
<http://802.11junk.com/jeffl/antennas/coffee2400/index.html
Note that the gain varies with frequency:
<http://802.11junk.com/jeffl/antennas/coffee2400/slides/gain-01.html
The NEC model is directly stolen from Trevor Marshall's at:
<http://www.nec2.org/wlan.htm

That's also without any additional losses such as surface conduction
losses, connector loss, coax loss, etc.  The final antenna at the end
of a few feet of lossy coax cable will probably be about 2-3dB less.

If you paid for 12dBi and are only getting 8dBi, ask the vendor for

If you want to do something useful, figure out what I did wrong with
the coffee can design speadsheet.  It's close, but not perfect.
<http://802.11junk.com/jeffl/rf-calc/Coffee-can05.xls

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: The "Cantenna" has not 12 dBi!!!

Dear Jeff,

I have seen your cantenne model. But where is your NEC-file for the
cantenna? I will show you, where you have model errors. Did you ever
performed an average gain test? If not, you should do this allways
first. Also all warnings in your model should be removed or checked!
Otherwise, you will get wrong results.
Especially, you should not have surface patches (tin can) nearby your
feed point!

Regards,
Aziz

Re: The "Cantenna" has not 12 dBi!!!

Hell Jeff,

I have found your excel sheet and did the model calculation. Your feed
have to be optimized. Also, some parts (surface patches) nearby the
feed, must be removed.

My model with surface patches:
Tin can diameter: 100 mm
Length: 135 mm
Lg/4: 44.452 mm
My model gets round about 7.7 dBi with the same dimensions. Calculated
total gain is 8.3 dBi, average gain test correction is 0.6 dBi. 8.3 -
0.6 = 7.7 dBi.

Model with wire grid (more accurate):
Total gain is 8.4 dBi without error (average gain test=1.0 (-0 dBi
correcting factor)).

Of course, with 198 mm diameter flare for the cantenna, you get 12 dBi
gain.
But the original cantenna can not be have 12 dBi!!!! It is a cheap
marketing issue.

Aziz

Re: The "Cantenna" has not 12 dBi!!!

oeguet@gmx.de hath wroth:

Sorry.  My Jalbum 7.1 photo album software buried the NEC2 files. Some
of the various NEC2 files are:
http://802.11junk.com/jeffl/antennas/coffee2400/coffee.nec
http://802.11junk.com/jeffl/antennas/FullWavePlateReflector/Plate02.nec
http://802.11junk.com/jeffl/antennas/HandHeld/HandHeld.nec
http://802.11junk.com/jeffl/antennas/HawkDish08/HawkDish08.nec
I'll make them visible when I figure out how.

Sure.  I'm interested.  However, I would prefer you find whatever we
did wrong with the Excel speadsheet which can generate the NEC file.

Yep.  It fails with a value of about 2.0.  1.0 is perfect.  I haven't
chased down the cause.  I've made it worse, but not better.  L.B.
Cebik offered some sage advice from about 2.5 years ago on the model,
which none of the perpetrators (including me) have done anything
<http://www.robomod.net/mailman/private/nec-list/2005-January/001398.html
You may need to register to view this.  Please ask if you want me to
email the message.

I did, but couldn't determine how to fix it.  Believe me, I tried.  I
think the problem is fairly universal because all of the coffee can
models I've found on the web have exactly the same problem.  The model
is even included as a sample with several packages.  Despite the
errors, the field test results closely resembles the model.

4NEC2 shows:

etc...

That's from the overlapping wires at the base of the conical feed.  It
was too much work to try to get them each positioned so there's no
overlap.  I'll replace the cone with a single wire feed (as in the
spreadsheet), which gets rid of that error but narrows the bandwidth.

Some warnings can be safely ignored.

Yep.  It is quite close, but not touching.  I'll try punching a hole
in the side of the can, under the conical feed, and see if that helps.
However, not for a few days.  I've got too many projects going and
this one is going to take some real work.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: The "Cantenna" has not 12 dBi!!!

Hello Jeff,

I have sent you some cantenna models via email. They are very long, I
couldnt post it here.

Here is the source code of my cantenna model (not 4nec2/nec2/nec4
compatible!):
As I mentioned in email, the source antenna model have to be compiled.
---------------------------------
CM Cantenna WLAN Antenna Model at 2.437 GHz
CM (C) 2007 by Aziz Oeguet
CM File: Cantenna2G4Hz.txt
CE

#include "Common.txt"
#include "PP4NEC2Defs.txt"

ofsx =3D -0.05          // Offset x-Achsenverschiebung (zur besseren 3D-
Darstellung)

//--- Kontrollschalter (Switches) f=FCr Modellkonfiguration ---
#ifndef CANTENNA_TRICHTER
CANTENNA_TRICHTER =3D 1 // Trichter-Blende (0=3Dkein, 1=3Dmit)
#endif

#ifndef CANTENNA_WRMODE
CANTENNA_WRMODE   =3D 1 // Drahtmodus (0=3DSurface-Path, 1=3DWire-Modus)
#endif

#ifndef CANTENNA_CALC
CANTENNA_CALC     =3D 0 // Cantenna parameter berechnen (1=3Dberechnen,
0=3Dauf manuellen Wert lassen)
#endif

#pragma symode =3D _SYMODE_REUSE

//--- Feeder(Erreger)-Parameter (Lambda/4-Element) ---
Feed_Durchmesser =3D 0.0015          // Antennendrahtdurchmesser
Feed_nSeg    =3D 9                   // Anzahl Segmente des
Antennendrahtes
Feed_Tagnr   =3D 1000                // Draht Tagnummer-Start
Feed_Segnr   =3D 1                   // Segment-Number des Erregerst=FCcks

#if !CANTENNA_CALC
Feed_Len =3D 0.0308    // Antennendrahtl=E4nge
#else
Feed_Len =3D lambda/4  // Antennendrahtl=E4nge (Wellenl=E4nge/4)
#endif

Feed_Delta =3D Feed_Len/Feed_nSeg    // Segment-L=E4nge (Antennendraht)

//--- Cantenna-Parameter (Tubus) ---
TubusnSegLen        =3D 15    // Anzahl der Segmente in Tubus-L=E4nge
TubusnSegMantel     =3D 32    // Anzahl der Segmente im Tubus-Mantel

TrichternSegLen     =3D 12    // Anzahl der Segmente in Trichter-L=E4nge
TrichternSegMantel  =3D 32    // Anzahl der Segmente im Trichter-Mantel

TubusDurchmesser    =3D 0.1   // Tubus-Durchmesser
TrichterDurchmesser =3D 0.198 // Trichter-Durchmesser
TrichterLen         =3D 0.086 // Trichter-L=E4nge

#if !CANTENNA_CALC
//--- Cantenna Parameter manuell ---
TubusLen  =3D 0.135           // Tubus-L=E4nge
Feed_Dist =3D 0.044452           // Erregerabstand zu hinteren Wand
#else
//--- Cantenna Parameter berechnen ---
DLc       =3D 1.706*TubusDurchmesser
DLg       =3D 1/sqr((1/(lambda*lambda))-(1/(DLc*DLc)))
TubusLen  =3D DLg*3/4         // Tubus-L=E4nge
Feed_Dist =3D DLg/4           // Erregerabstand zu hinteren Wand
#endif

Feedzpos  =3D -TubusRadius    // Erregerfusspunkt (unten)

//--- Feeder ---
// Erregerspeisedraht
GW Feed_Tagnr Feed_nSeg  0 0 Feedzpos-Feed_Delta/2   0 0 Feedzpos

// winziger Anschlussstummel unten (NEC2 Warnung umgehen)
GW Feed_Tagnr+1 1  0 0 Feedzpos-Feed_Delta/2   0 0 Feedzpos-Feed_Delta/

p1x =3D Feed_Dist-0.04
p1y =3D -0.03
p1z =3D-0.03
p2x =3D Feed_Dist+0.11
p2y =3D 0.05
p2z =3D 0.03

//--- Hotspot (am Erreger in der N=E4he keine Objekte generieren) ---
#Hotspot point=3D_HS_OUTSIDE Feed_Dist 0 Feedzpos 0.005

// F=FCr hintere Wand des Tubus n=F6tig, da Vierecke im Mittelpunkt zu
Dreiecken werden.
#pragma limits=3D1, minwirelen=3D0.001, minareasize=3D0.000001

//--- Tubus generieren ---

#if CANTENNA_WRMODE
// Parameter f=FCr Wire-Modus
#pragma mode=3D _MODE_WR, wrnumseg =3D 1, wrtagstart=3D2000, wrtaginc =3D 1,
#else
#pragma mode=3D _MODE_SP
#endif

//--- Tubus um Erregerabstand nach hinten verschieben ---

#Move -Feed_Dist 0 0

w1 =3D 180
w2 =3D w1+360

// Tubus generieren

// Hintere Wand (Ring) generieren

// Trichter generieren
#if CANTENNA_TRICHTER
#Pipe TrichternSegMantel TrichternSegLen TubusLen 0 0 w1 w2
_A1
#endif

#Transform // Transformation abschliessen (Move)
//--- Ende Tubus-Verschiebung ---

// Achsen-Transformation (um aus dem Nahfeld rauszukommen)
#if !CANTENNA_TRICHTER
GM 0 0 0 0 0 -TubusLen+Feed_Dist+ofsx 0 0 0
#else
GM 0 0 0 0 0 -TubusLen+Feed_Dist-TrichterLen+ofsx 0 0 0
#endif

// End-Of-Geometry
GE 0

EX 0 Feed_Tagnr Feed_Segnr 0 1.0 0.0
LD 5 0 0 0 62900000

// Extended-Wire-Kernel einschalten
EK 1

//--- Frequency Parameter and Execute ---
FR 0 1 0 0 freq 1
RP 0 91 181 1001 -180 0 2 2
EN
-----------------------END-------------------

Re: The "Cantenna" has not 12 dBi!!!

The construction of a waveguide requires a
minimum amount of understanding of E and H
fields. In order to realize the maximum gain
quite  few principles must be gotten right..My
opinion, "it's not for everybody.."

Re: The "Cantenna" has not 12 dBi!!!

cantenna with maximum 24dBi? --> 'WLAN-SAT-FORUM
Forums-viewtopic-Ultimate wifi antenna TinCan Enhancers - part-2 ...'
(http://www.wlan-sat.com/modules.php?name=Forums&file=viewtopic&t=4782 )

------------------------------------------------------------------------
http://www.wirelessforums.org

Re: The "Cantenna" has not 12 dBi!!!

This is not exactly a cantenna, but a horn antenna uses the same
principle.  16dBi gain:
<http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=12624

How to grind the numbers for a horn antenna:
<http://users.skynet.be/chricat/horn/horn-javascript.html

The cardboard and aluminum foil horn antenna:
<http://www.seattlewireless.net/index.cgi/CardboardHorn

SETI "horn of plenty"
http://www.setileague.org/photos/wghorn/pyramid.jpg
http://www.setileague.org/photos/wghorn.htm
20dBi gain at 1500MHz.  My guess(tm) is about 24dBi at 2.4GHz.  Note
the size of the horn required to get that gain as compared to the
Slovanian cantenna.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: The "Cantenna" has not 12 dBi!!!

Jeff Liebermann;120986 Wrote:

it´s some kind of "booster" to a cantenna...i didint get 24dB, but
around 17dB..it´s not bad for very low-cost antenna.

I use this freeware for horn antennas / conical horns /parabolic /lens,
its great because gives a template according to the frequency we want. i
import the postscript file to corel draw.

and file sharing service!' (http://depositfiles.com/files/1078122 )

------------------------------------------------------------------------
http://www.wirelessforums.org

Re: The "Cantenna" has not 12 dBi!!!

I've never heard of a booster.

I suggest you get it from the authors web site at:
<http://www.w1ghz.org/software/hdl_3b4.zip
<http://www.w1ghz.org/antbook/contents.htm (see other programs)
It is a nifty program for designing horns, but it's not terribly
interactive or educational.  For example, you have to know in advance
the size of 2.4GHz WR-340 waveguide.  Hint:
<http://www.microwaves101.com/encyclopedia/waveguidedimensions.cfm

Although this dish feed horn design spreadsheet doesn't generate sheet
metal templates, it's much more useful:
<http://www.setileague.org/software/feedhorn.xls
More of the same:

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: The "Cantenna" has not 12 dBi!!!

Jeff Liebermann;121236 Wrote:

a booter is what  i call a conical horn..

Jeff Liebermann;121236 Wrote:

great sites, thanks!

'Wi-Fi. Krasnodar. Horn antenna. Ðóïîðíûå àíòåííû.'
(http://vbm.lan23.ru/wifi/horn.html ) --> here it is a rectangular Horn
antenna for 2.4ghz with 33dB, it´s not very pratical to use...but it´s
impressive.

at this moment i´m using Patch microstrip antennas, very simple to
build...and give good results, the problem in building PCB patch
antennas is to find the correct type of PCB due to his dielectric
values, i have a 14dBi in a bad bakelite-PCB that works great, but in
other antennas dont work very well...maybe FR-4 PCB would have better
results.

------------------------------------------------------------------------
http://www.wirelessforums.org

Re: The "Cantenna" has not 12 dBi!!!

Here's another large 2.4GHz horn antenna used in the 2003 WiFi long
distance (DX) contest:
<http://www.wifi-shootout.com/archive/2003/index.htm
(Near bottom of page).  Made with a metal tubing frame and covered
with aluminium window screen wire mesh.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: The "Cantenna" has not 12 dBi!!!

Nice.  There was also some ham radio 2.4GHz horns with a similar case
of elephantitis.   It's actually not a horrible as it looks and is
very easy to fabricate.  It's also not a critical in construction and
tuning as a parabolic dish.  However, a horn is big and ugly.

Bakelite?  I think you mean phenolic, which is the light brown paper
and glue cheap junk that absorbs moisture like a sponge and is very
lossy at 2.4GHz.  Even G10/FR4 is better than phenolic.  However, if
you want quality, look into air dielectric (standoffs), polysulfone,
or PTFE (RTDuriod).

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: The "Cantenna" has not 12 dBi!!!

It's crap.  G10/FR4 is cheap and commonly available.

Correct.  Although there's a bit of a question of from where to where
to measure.  Hmmmm.... No NEC cards included so I can't run his
numbers through 4NEC2.  The first paragraph on the page is speculative
baloney.

Nope.  The traces between the feed point and the beginning of the
dipole elements might be 50 ohms (they're not, but close enough).
However, the other elements a fairly high impedance and should be
quite a bit thinner than shown.

Yep, 1:1 balun is needed.  That can be made from coax cable.  The
"extra" two quarter wave sections between the feed point and the
dipole is rather questionable and mostly useless.

What are you trying to accomplish?
Duz it have anything to do with the original question?
--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: The "Cantenna" has not 12 dBi!!!

Jeff Liebermann;122698 Wrote:

how can i find the impedance for the microstrip width?

Jeff Liebermann;122698 Wrote:

sorry, this has nothing to do with the original topic of cantenna..

i which to build that omni PCB, but i only recently started at RF..so i
dont have enough knowledge to make the antenna.

that´s a very big horn, how much dBi that antenna will have?

the world record wireless distance is 237.36miles, 'link'
(http://tinyurl.com/2tyz2m )

------------------------------------------------------------------------
http://www.wirelessforums.org

Re: The "Cantenna" has not 12 dBi!!!

<http://mcalc.sourceforge.net/>
<http://www.microwaves101.com/encyclopedia/calmstrip.cfm
<http://www.microwaves101.com/encyclopedia/calsstrip.cfm
<http://www.emclab.umr.edu/pcbtlc/strip.html
Lots more under stripline and microstrip.

Well, ok.  Low gain antennas are easy enough.  High gains antennas are
difficult.

Dunno.  I need dimensions to run a model.  It's late.  I'm tired.
Maybe later...

Amazing.
--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: The "Cantenna" has not 12 dBi!!!

Jeff Liebermann;121950 Wrote:

check out the FA-20 antenna in the link..it´s a very simple high gain
antenna.
I build also two 14dBi patch antennas showed in the link...they work
great.

Jeff Liebermann;121950 Wrote:

i know its terrible for 2.4ghz...but yet it´s the cheapest PCB i can
get.

i know this is getting very offtopic, but i have this link for a omni
PCB antenna: 'David Kittle's Collinear Antenna'
(http://people.wwc.edu/student/kittda/Prop/collinear /)
i´m trying to understand the design to use in different PCB´s..

i think the omni is made according to this:
-for the 57mm section= (lambda/2)*copper velocity factor
-for the 27mm section= (lambda/4)*copper velocity factor

-for the microstrip width i just use a simple software like AppCAD to
calculate a 50ohm microstrip line according to the PCB specifications,
right?

-regarding about feeding the antenna, a balun to connect the two
sections of the antenna? in the link nothing is mentioned how to feed
the antenna.

I appreciate any help...

------------------------------------------------------------------------