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Problem with Resonances in Combline Filter

 
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kashyapastron



Joined: 30 May 2008
Posts: 8
Post15 Aug 2008 7:46   Problem with Resonances in Combline Filter
Hello,

I am designing a 5 pole combline filter. The problem I have been facing is that whenever I simulate a combline filter of order more than 3, the S11 response always shows lesser no of resonances and hence getting the required bandwidth and ripple levels is very hard. I tried to use both peter martin's equations and also the eigen mode analysis method to determine the rod spacing but to no avail. I'm attaching a HFSS file with one such simulation where only 3 resonances are distinct for a 5-pole filter. Please help

Thanks

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G4BCH



Joined: 10 May 2006
Posts: 96
Helped: 26
Post15 Aug 2008 8:23   Re: Problem with Resonances in Combline Filter
I can't read your file, but how distinct the VSWR ripples will be depends upon the amplitude response of your design. A Bessel response will only show one dip at centre frequency, but a 1dB Chebyshev will clearly show all 5.

If want a quick design tool then download Ansoft DesignerSV, the filter design wizard is easy to use and gives some good start values. If you have HFSS you probably already have Designer or something similar anyway.
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kashyapastron



Joined: 30 May 2008
Posts: 8
Post15 Aug 2008 10:55   Re: Problem with Resonances in Combline Filter
Hello,

I'm attaching the zip file and hope you can see it. The amplitude response I have chosen is chebyshev with 0.1dB ripple. That is the reason why I'm looking for 5 resonances. Thanks for your reply.

I hope you can help me now

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kashyapastron



Joined: 30 May 2008
Posts: 8
Post18 Aug 2008 14:38   Re: Problem with Resonances in Combline Filter
Hello

I need help urgently !!
Thanks
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james cook



Joined: 04 Sep 2005
Posts: 201
Helped: 7
Post20 Aug 2008 14:08   Problem with Resonances in Combline Filter
Try to use the cosimulation method with ansoft designer. export the S parameter into the circuit and tune it in the linear simulator to get correct respond. U
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