Electronics > RF, Microwave, Ham Radio

Cantenna implementation: just how tricky is it?

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MarkMLl:
A few days ago I needed to check for the presence of a WiFi AP (possibly not actively advertising its availability). I knocked together a cantenna in a hurry from a somewhat-undersized drinking chocolate can, its off-axis rejection was good but its rear-lobe was disappointingly strong: I suspect because the can was too short so the probe was too close to the centre.

I've come across https://web.archive.org/web/20210512030616/https://www.wifi-antennas.com/topic/52-dual-band-cantenna/ which is interesting, but it appears to be an old discussion which went quiet.

* Can anybody comment on the computed dimensions?

* Does anybody recognise the software used for the gain simulations? Is there a half-decent free alternative?

* If having to use "rules of thumb", how does one allow for the horn which various people suggest adds substantial gain?

* If fabricating from "found" components (aluminium ducting, stainless cans etc.) how paranoid does one have to be about good contact? Should everything be TIG welded to penetrate passivation layers?

* How disruptive are internal steps or ridges of a couple of mm at joins likely to be?

Hope that lot makes sense and sparks somebody's interest. There seems to be an enormous disparity between the way people say "this stuff is non-critical" vs the amount of care that goes into professionally-manufactured waveguides.

joeqsmith:
I tried to make one from a couple of bean cans soldered together. 

https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg4166587/#msg4166587

We tried to 3D print some microwave horns and compare them with a production part. 

MarkMLl:
I was in a bit of a hurry... can I used was plated steel (not stainless since it appears to be magnetic), about 84mm diameter 125mm long with 30.6mm probe on an SMA about 56mm from back. NanoVNA suggests it's broadband centred on the the 2.43 GHz region with an SWR of 1.4 and doesn't care whether the plastic lid is fitted (to add a bit of strength).

Definitely better than a WiFi whip (I tried both on location since nobody was actually shooting at me). However now that I've got this far I'm interested in how to "do things properly" without having to learn thin-wall TIG welding etc. :-)

Marsupilami:
Software is CST. Not cheap.
OpenEMS might be a solution for you but it has a learning curve with scripting and stuff.
There were threads here too in the past about affordable/ free and open source em sim software.

vk6zgo:

--- Quote from: MarkMLl on June 10, 2023, 10:32:12 pm ---I was in a bit of a hurry... can I used was plated steel (not stainless since it's magnetic), about 84mm diameter 125mm long with 30.6mm probe on an SMA about 56mm from back. NanoVNA suggests it's broadband in the 2428 MHz region and doesn't care whether the plastic lid is fitted (to add a bit of strength).

Definitely better than a WiFi whip (I tried both on location since nobody was actually shooting at me). However now that I've got this far I'm interested in how to "do things properly" without having to learn thin-wall TIG welding etc. :-)

--- End quote ---

I very much doubt that the magnetic properties of stainless or plated steel have any effect at 2.4 GHz.
Certainly, UHF Yagis are quite commonly made of stainless steel for durability.

Interestingly, the term "Cantenna" has a quite different meaning, as an RF test load consisting of a large tin can full of transformer oil with a biggish 50 \$\Omega\$ resistor suspended in it

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