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Need a Filter structure w/Good Return Loss - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.

Post subject: Need a Filter structure.
Unread post Posted: Fri Jan 28, 2005 3:14 am

Need a Filter Structure, which has Good Return Loss for both pass band and out band rejection.

Do remember seen once in Eagleware Demo.


Post subject: Use a diplexer
Unread postPosted: Fri Jan 28, 2005 10:14 am

Good Luck! Sounds like you need to use a diplexer where the out of band energy is dumped into a load.


Kirt Blattenberger
Post subject: It's kind of cheating, but...
Unread postPosted: Fri Jan 28, 2005 5:16 pm
Site Admin
User avatar

Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location: Erie, PA
Greetings Arool:

If you can afford the added insertion loss, one way to get good return loss both inband and out-of-band is to place an attenuator at the input of the filter.

The return loss improvement is 2x the attenuation value. Be aware though that an attenuator designed to be 3 dB into a 50 ohm load will not be 3 dB into any other load. I say this because your filter's out-of-band impedance willl not be 50 ohms. A simulator such as Eagleware's will make easy work of it for you.

- Kirt Blattenberger :smt024


Post subject:
Unread postPosted: Fri Jan 28, 2005 10:50 pm

To Kirt Blattenberger:
I want to know a good RF simulator tools,Could you introduce a good one? Thanks a lot


Kirt Blattenberger
Post subject:
Unread postPosted: Sun Jan 30, 2005 11:36 pm
Site Admin
User avatar

Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location: Erie, PA
QQ wrote:
To Kirt Blattenberger:
I want to know a good RF simulator tools,Could you introduce a good one? Thanks a lot

Greetings QQ:

I would be remiss to not recommend the two simulators offered by advertisers on RF Cafe:

Aplac (based in Finland)

Eagleware (based in Georgia, USA)

Otherwise, there are numerous programs of varying complexity for you to chose from, depending on your need. If you have not already done so, please take a look at the many listings on the Software page on RF Cafe.

Thanks for writing.

- Kirt Blattenberger :smt024


Post subject:
Unread postPosted: Wed Mar 09, 2005 12:36 am

I found a nice pdf file from CERN by J.M. Belleman
PS/BD/Note 2002-193(Tech) that offers solutions for 3-7th order filters with very high out of band return loss.


Oleg Pozdeev
Post subject:
Unread postPosted: Wed Mar 09, 2005 12:05 pm


There are two well known ways to build a BPF filter perfectly matched in- and out of band.
The first one is so called directional filter scrutinized in many school books including microwave bible by Matthaei, Young and Jones.
The second employs two identical BPF’s connected in between of two quadrature hybrids (similar to balanced amplifier)


Posted  11/12/2012
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