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Wideband Filter - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


Antonio
Post subject: Wideband Filter Posted: Tue Nov 27, 2007 6:42 am

Captain


Joined: Sat Jun 16, 2007 12:26 am
Posts: 12
Can anyone tell me:

Why the Return Loss performance is poor in Wideband Filters?

Or

Why is it difficult to get good Return Loss performance in Wideband Filters?


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IR
Post subject: Posted: Tue Nov 27, 2007 4:01 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hi Antonio,

Wideband filters are those with a BW>10% of the center frequency

The reason for that is the same as why it is hard to design a wideband filter with low insertion loss. When you design a wideband filter, more resonators are required which increase the insertion loss and thus the return loss.


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Antonio
Post subject: Posted: Thu Nov 29, 2007 6:49 am

Captain


Joined: Sat Jun 16, 2007 12:26 am
Posts: 12
Hi IR,

Thanks for your reply..

Can you please explain it with the help of circuits? A circuit containing combination of L and C and some tank circuits.


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IR
Post subject: Posted: Sat Dec 01, 2007 12:16 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hi Antonio,

The following article mentions this issue. It describes distributed (printed) filters. The principle is the same for both distributed and lumped filters.

http://www.eng.jcu.edu.au/Staff/Profile ... 81-Fil.pdf

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Jeanalmira
Post subject: Posted: Mon Dec 24, 2007 9:25 pm

General


Joined: Tue Mar 15, 2005 11:43 pm
Posts: 65
Location: Singapore
Hi Antonio,

I agree with the above posts.
But keep in mind that by adding more resonators, there will be more insertion loss resulted.
The difficulty in getting good Return Loss performance in Wideband Filters is somehow related to the Q concept.
It depends how good you want the performance is. The smaller insertion loss and the higher return loss require higher Q, which means it will give sharper response.

I hope it helps.

Regards,
Jean








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