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
>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.
Show me. I do designs and models.
>If you check and correct this desing errors, you will get only a
>performance of 8 dBi.
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.
>It is not true, which the cantenna has 12 dBi! Keep in mind.
>Aziz
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
your decibels back.
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>
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!
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.
Sure. I'm interested. However, I would prefer you find whatever we
did wrong with the Excel speadsheet which can generate the NEC file.
>Did you ever
>performed an average gain test?
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
about:
<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.
>If not, you should do this allways
>first.
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.
>Also all warnings in your model should be removed or checked!
4NEC2 shows:
> Warn.: too sharp angle or too short/thick segment(s) for Wires 2 (tag 2) and 3 (tag 3)
> Warn.: too sharp angle or too short/thick segment(s) for Wires 2 (tag 2) and 4 (tag 4)
> Warn.: too sharp angle or too short/thick segment(s) for Wires 2 (tag 2) and 5 (tag 5)
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.
>Otherwise, you will get wrong results.
Some warnings can be safely ignored.
>Especially, you should not have surface patches (tin can) nearby your
>feed point!
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.
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.."
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
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.
>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've never heard of a booster.
>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.
>
>hdl_3b4 --> 'Download hdl_3b4.zip - DepositFiles.com - the best upload
>and file sharing service!' (http://depositfiles.com/files/1078122)
The download site is full.
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:
<http://www.setileague.org/software/spreadsh.htm>
The download site is full.
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:
<http://www.setileague.org/software/spreadsh.htm>
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.
>'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.
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.
>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.
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).
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.
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.
Quote:
Originally Posted by Jeff Liebermann
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).
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
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 know its terrible for 2.4ghz...but yet it´s the cheapest PCB i can
>get.
It's crap. G10/FR4 is cheap and commonly available.
>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
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.
>-for the microstrip width i just use a simple software like AppCAD to
>calculate a 50ohm microstrip line according to the PCB specifications,
>right?
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.
>-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.
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.
>'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.
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.
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.
how can i find the impedance for the microstrip width?
Quote:
Originally Posted by Jeff Liebermann
What are you trying to accomplish?
Duz it have anything to do with the original question?
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.
Quote:
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.
that´s a very big horn, how much dBi that antenna will have?
the world record wireless distance is 237.36miles, link
>> 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.
>how can i find the impedance for the microstrip width?
<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.
>i which to build that omni PCB, but i only recently started at RF..so i
>dont have enough knowledge to make the antenna.
Well, ok. Low gain antennas are easy enough. High gains antennas are
difficult.
>> 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.
>that´s a very big horn, how much dBi that antenna will have?
Dunno. I need dimensions to run a model. It's late. I'm tired.
Maybe later...
The "Cantenna" has not 12 dBi!!! 
Linear Mode
