[SOLVED] WiFi harmonic problem

[guytoub]

Hello ,

i've designing a receptor at 9.9 Ghz but due to the amplifier band i've got a wiFI harmonic at 9.6 GHz .
my question is what is the simple way to kill this harmonic.
i'm looking for a cavity filter but i would like to know if a simple thing like a stub may works?

regards

 

[tony_lth]

No. The stub will absorb both signal and noise.
Cavity filter is a better solution.
I don't know the detail of the freq of signal and noise, would you give more details?

 

[vfone]

The golden rule when dealing with desense issues is that first try killing (or minimize) the source of the interference, and only if this doesn't give a solution, to look and help the "victim" (shields, filtering, layout, etc.).

 

[guytoub]

No. The stub will absorb both signal and noise.
Cavity filter is a better solution.
I don't know the detail of the freq of signal and noise, would you give more details?

thanks, I can not give details, but I thought I would go to the cavity filters

--- Updated Dec 2, 2020 ---

The golden rule when dealing with desense issues is that first try killing (or minimize) the source of the interference, and only if this doesn't give a solution, to look and help the "victim" (shields, filtering, layout, etc.).

i can't minimize the source because it coupld be everything that works a 2.4 Ghz .
i'try to shielding the amplifiers and made the microtrips lines as short as possible

 

[tony_lth]

Maybe you just need a pre-filter before the LNA, to filter 2.4GHz.
A 9.xGhz filter can be made by microstrip, typically application with about 10% bandwidth. And with smaller size and better cost than cavity.
And you need a cavity to cover your circuit, etc.

 

[guytoub]

Maybe you just need a pre-filter before the LNA, to filter 2.4GHz.
A 9.xGhz filter can be made by microstrip, typically application with about 10% bandwidth. And with smaller size and better cost than cavity.
And you need a cavity to cover your circuit, etc.

a prefilter will not work because the 2.4 Ghz signal is not on my card, but these are the signals emitted by connected cellphones or watches.
I would like to design a microstrip filter to deal with this problem but I do not have enough experience to know, which substrate would be best, strong permitivity or not? strong substrate thickness or not.
I was thinking of coupled lines rather than hairpin.
I have the ADS software so if you have any ideas or examples, I will take it.

regards

 

[tony_lth]

1st you need to identify which signal the 9.6G is.
receive the 9.6GHz with spectrum analysis, and if you see an signal with bandwidth about 1M or more, it should be the wifi harmonics.
But if the signal's BW is very small, just like a point freq, then it should be a radar signal.
I designed a metreology radar at 9.6GHz. If you receive the rader signal, then there should have a radar station near you.
Using microstrip filter could possible filter the 9.6GHz.
The substrate can be RO4350B.
You can design the passband 9.9G ~10.5GHz, the stop band can be 9.6GHz.
The microstrip may have freq shift about 100MHz, so just evaluate it. This is the normal design, and you can do it with textbook direct.

there are also some special design, such as remove some ground under the microstrip, and it can reach 3% bandwidth.
that is more complex, and you need to simulate it with CST or HFSS etc.
Good luck.

 

[BigBoss]

If the third Harmonic of a WiFi system may able to disturb any kind of receiver, there is a serious problem because third harmonic must be lower than from a certain power level.You should solve your problem "at the Source". If there is a simple LC Filter at the Output of the WiFi system, you can replace it with a Ceramic Band Pass filter with a high skirt attenuation.Otherwise, applying every filtering on Receiver side will disturb the characteristics of the receiving.

 

[guytoub]

If the third Harmonic of a WiFi system may able to disturb any kind of receiver, there is a serious problem because third harmonic must be lower than from a certain power level.You should solve your problem "at the Source". If there is a simple LC Filter at the Output of the WiFi system, you can replace it with a Ceramic Band Pass filter with a high skirt attenuation.Otherwise, applying every filtering on Receiver side will disturb the characteristics of the receiving.

I can only resolve my problem on my receiver because I am disturbed by all 2.5Ghz broadcasts, wifi, bluetooth, etc. Since I have a wideband amplifier which accepts -50 dBm at the input and that I have a gain of 45dB, I am bothered by a low power harmonic. I think the filter can solve my problem or otherwise I will try to shield my amp.

--- Updated Dec 5, 2020 ---

1st you need to identify which signal the 9.6G is.
receive the 9.6GHz with spectrum analysis, and if you see an signal with bandwidth about 1M or more, it should be the wifi harmonics.
But if the signal's BW is very small, just like a point freq, then it should be a radar signal.
I designed a metreology radar at 9.6GHz. If you receive the rader signal, then there should have a radar station near you.
Using microstrip filter could possible filter the 9.6GHz.
The substrate can be RO4350B.
You can design the passband 9.9G ~10.5GHz, the stop band can be 9.6GHz.
The microstrip may have freq shift about 100MHz, so just evaluate it. This is the normal design, and you can do it with textbook direct.

there are also some special design, such as remove some ground under the microstrip, and it can reach 3% bandwidth.
that is more complex, and you need to simulate it with CST or HFSS etc.
Good luck.

it is the harmonics that bother me, I tut measure with a dynamic analyzer. I will try to shield my amps and design a filter with your advice. thank you

 

[BigBoss]

I can only resolve my problem on my receiver because I am disturbed by all 2.5Ghz broadcasts, wifi, bluetooth, etc. Since I have a wideband amplifier which accepts -50 dBm at the input and that I have a gain of 45dB, I am bothered by a low power harmonic. I think the filter can solve my problem or otherwise I will try to shield my amp

So shielding is an option and using a high directivity antenna is another option.
Additional Option is to use Spread Spectrum but it's quite difficult to implement. Spread Spectrum systems are used in Military Applications is to immune against Jamming Signals.

 

[guytoub]

Thank you for your help .
I chose as a solution the shielding of my system and a filter.