Author Topic: Cut steps when tuning a 2.4g meander antenna length.  (Read 1241 times)

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Offline PsiTopic starter

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Cut steps when tuning a 2.4g meander antenna length.
« on: May 18, 2023, 12:00:13 pm »
When cutting a 2.4ghz meander antenna shorter and shorter to tune the length, how much length should I be cutting/grinding off each time to avoid missing a good antenna length?  eg 1mm? less?

I'm using this coil layout, except without the exact FR4 edge positioning that they spec.
Also I have a longer feed line to the antenna, 4mm or so surrounded by GND plane and via stitching.
https://www.st.com/resource/en/application_note/an5129-low-cost-pcb-antenna-for-24ghz-radio-meander-design-for-stm32wb-series-stmicroelectronics.pdf

« Last Edit: May 19, 2023, 11:21:19 am by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline geggi1

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Re: Cut steps when tuning a 2.4g meander antenna length.
« Reply #1 on: May 18, 2023, 04:52:44 pm »
1mm is almost 1% of a full wavelength and that will give a big difference in in the resonant point of the antenna.
I would recommend to trim as short lengths as possible.

Another way to get it into resonance is to use a trimmer cap in the matching capacitors see page 4.
Option one is to use one trimmer capacitor 60pF or something and trim for the highest output.
Option two is to use a fixed 120pF and a trimmer at the same size, trim for the highest output.
The last potion is to play around with fixed caps.
 

Offline PsiTopic starter

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Re: Cut steps when tuning a 2.4g meander antenna length.
« Reply #2 on: May 22, 2023, 12:00:39 pm »
Is it better to do length tuning with the RX or TX antenna?
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline coppercone2

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Re: Cut steps when tuning a 2.4g meander antenna length.
« Reply #3 on: May 23, 2023, 12:46:18 am »
do strokes of a file
 

Offline geggi1

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Re: Cut steps when tuning a 2.4g meander antenna length.
« Reply #4 on: May 23, 2023, 04:10:33 am »
Is it better to do length tuning with the RX or TX antenna?

Normaly it is better to tun the lenght but on higher frequencies it is hard because just tiny changes will give large changes resonant frequency.
One way to get around this is to make the antenna wide band to simplifie the tuning.
 

Offline Hamelec

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Re: Cut steps when tuning a 2.4g meander antenna length.
« Reply #5 on: May 28, 2023, 02:57:55 pm »
take a tiny piece of sheet metal e.g aluminium foil, put it on your FR4 board near the antenna and move it around for tuning with a toothpicker, always watching the s11. Glue it with some silikon (and readjust it).
 


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