Problem with DCS band 2nd and 3rd harmoinc

[mckinson]

About the harmoinc ?

Hello guys ! I found the DCS band second harmonic and 3th is very high for the mobile .I try tuning the match network from PA to switch ,but no improvemet !
I also find that is very high from tranceiver ,no pass PA . Now ,I have no idea !Any guys can give me some suggestion .best regards !

 

[wpsch]

About the harmoinc ?

Is the emission conducted or radiated? If conducted, one quick method is to try to use around 2.7pF 0402 shunt capacitor to form your matching network to kill the second harmonic, around 1.8pF to kill the third. The location closer to the source, the more suppress can get.

Have you also suspected the harmonics are from the switch?

 

[mckinson]

About the harmoinc ?

But if add the capacitor ,maybe cause the impedance mismatch . I don't know how to fix this problem ? Best Regards!

 

[wpsch]

About the harmoinc ?

yep..., the matching network may be changed. May be more components needed. Some calculation/simulation and on-board fine tuning seems to be unavoidable. Just a suggestion.

 

[flatulent]

Re: About the harmoinc ?

Use a topology that is low pass or band pass for the matching. Also use one with more elements.

 

[mckinson]

About the harmoinc ?

But now the harmonic is also very big ,from the tranceiver .I don't why ? Maybe the VCO is interfered , do you think so ?Best regards !

 

[vfone]

Re: About the harmoinc ?

The harmonics from the transceiver in DCS1800 is very high? May I ask you how did you measure? And what is your transceiver spec for harmonics?
You have a different post about the same problem using CX77304

I can tell you, if you are using the right link budget (LPF, diplexer, etc) this PA will pass without problems any harmonics test.
As the other guys said if you are using a low-pass filter at the PA output, which includes a 2.7pF 0402 cap (resonating frequency = DCS1800 2nd harmonic), will minimize your harmonics at least 20dB.

 

[mckinson]

About the harmoinc ?

Hello ,Vfone ,yes you are right .The 2.7p capacitor can filter the DCS 2nd haumonic. But the match network is mismatch ,maybe cause the other problem , peak phase error , power ripple ,switchig spectrum .......Do you agree with me ?

 

[vfone]

Re: About the harmoinc ?

No, I don’t agree. You don’t have any mismatch.
If you read my previous post, I said that you could use a LPF, that includes a 2.7pF shunt cap. That means, this cap is part of the LPF matching network.

 

[mckinson]

About the harmoinc ?

vfone ,yes. You are right .Thanks .But do you know how to confirm the match network is correct ?