How to improve return loss and reduce bandwidth in my filter

[citizen]

return loss in filter

hi to all,
i have designd a combline round rod filter (3.7-3.8ghz)but the return loss is not good in the pass band......
is tuning of the tap points may change return loss?
or any other solution for this ???????????
here i got the band width exactly double to my designd one .....
means when i designed for 100 mhz i got 200mhz bandwidth
and when i designd for 90 mhz i got 180 mhz band width

so any suggession to improve return loss and reduce my band width
( im thinking that by scaling means designing for 50 mhz will get 100mhz band width is it works for this filter)

i tried the some tips which are suggested here in this forum as
increse spacing and order but im not getting my required filter............
any one clarify these doubts plzzzzzzzzzzzzzzzzzz..............

thank you one and all

 

[Phytech]

filter return loss

Return Loss: by change and optimise tap position, you will be able to improve if your coupling coefficients are about right.

Bandwidth widening: typical for most commercial programs, especially for narrow band filters. You may read a paper publised by R. Levy about this.

 

[RF-OM]

Re: filter return loss

Could you please upload this paper or provide a link?

 

[citizen]

Re: filter return loss

Bandwidth widening: typical for most commercial programs, especially for narrow band filters. You may read a paper publised by R. Levy about this.

thank you for ur suggegsion
ya i tried ur suggesion that tap point tuning is lead to change in return loss but about band width............................
can u post that paper u have mentioned here.
thank you

 

[Phytech]

filter return loss

Please see the attachment for the paper I mentioned.

Added after 1 minutes:

Try again.

Added after 14 minutes:

It seems that I cannot upload the paper. it keeps on telling the following message:

Sorry but this file has already been posted! Better copy and paste following link into your post, where the same file is located:


Added after 6 minutes:

The paper was published in

IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 45, NO. 12, DECEMBER 1997, page 2094-9.

 

[citizen]

Re: filter return loss

oh.................
im not getting that paper it seems to be removed topic the message is generated that it is removed post.........
plz any one post that here plzzzzzz
really i tried other wise send that to my mail id

thank you

 

[RF-OM]

Re: filter return loss

Hi again,

I did it today in my office, so the file is on office machine. I will try not to forget tomorrow to find it and send to you. So please wait a day. I found it not by link, but into MTT library, it wasn't easy because I had only author and page number, but finally I found it.

BR,
RF-OM

 

[Phytech]

Re: filter return loss

There is another paper dealing with bandwidth expansion of combline filters published by I. Shapir and V. Shamir in IEEE MTT Symp. Dig 1996. The title is "Modeling Structure Parasitics in Combline Filters". If anyone can upload this paper, it would be very helpful in understanding the topic of bandwidth expansion of combline filters.

Added after 3 minutes:

RF-OM,

It's very nice of you unloading this paper. Somehow I could not uploaded the paper myself. I don't know what happened.

Hello,

Here is your paper. Enjoy it!

 

[citizen]

Re: filter return loss

yes this is also very useful paper for me.............
thank you once again

 

[RF-OM]

Re: filter return loss

I am glad to help you. The only problem with all these papers that old IEEE MTT archives is not in good order and search is a nightmare. Even when you have exact title as it was for this case, search was failed. There were two separate 1996 archives! What idiot made it? By the size it was not necessary to divide all 1996 year by two disks, probably they prepared these archives at different times and then just included into whole archive as it was. It is good to have a big library, but it is very hard to find the paper what you are looking for.