combline filter* synthesi*

Does anyone have experience in combline filters with slabline resonators?

I have to design a C-band band-pass filter and I've started out with CST MWS. I was able to get the passband nearly where I wanted it but I can't optimize it for example to a Butterworth response.

I even tried out an example filter from a G. Matthaei book and I had similar problems eventhough in the book the response was maximally flat.

I would like to have an opinion from someone, who has designed these kind of filters, if it's even possible to optimize the filter or is it still a thing which has to be done with a prototype? The only approximation I've made in my model was that I used PEC instead of real metal.

-lr116-

Dear friend,
I have been designing and implementing several combline and interdigital band pass filters in microwave range using coupled slab line and rectangular resonators. In these designs I always had to do some optimization in the prototype due to mechanical tolerances. Also in narrowband applications I never escape to have some tuning capabilities in the final filter.
I already made some combline filters with rectangular stubs and as in this structure the stubs are all in one piece of metal, in some applications, I had to provide tuning just for the capacitive load across the stubs getting a very good accuracy in terms of stub's coupling.
Another problem is the matching of the last stubs to 50 ohms. My preference when I have no constraints about physical size is to use two additional stubs as impedance transformers instead of tap the signal of from the last two filter stubs.
In terms of material, my preference is to use copper with silver plating for stubs and cavity. This is the best relationship between price and specification.
In terms of development tools I use PARFIL to do the synthesis of the filter. This program also has some sort of optimization capability.

That is it, I hope this help you.

NandoPG

Does anyone there has the experience of design a combline line filter of very narrow bandwidth using coaxial cavity structure?And what is the design method?

To Needbias
In the Matthaei's book you can find all that you need.

Thanks very much,I will try to have a look.

Combline filter if wide band then use Wenzel&Horton synthesis ,
case of narrow band use MYJ book (Mathaei) as a begining point, in practice narrow band combline filter are heavily dependent on size versus frequency. For small size low frequency they work nearly as Matheai equations(use Cristal for round rods design or Getsinger for rectangular bars, or better nowdays use the italian proffesors paper that give equations to solve easily the coupled lines dimensions).
The problem with narrow band comblines with big size (relative to frequency of use) is that you might design for a certain bandwidth, but measured data might show a much wider filter then your original design and simulation.
Look at paper that gives cure to that (Shafir,D.Swanson,S.Sharir in IEEE-MTT).
The basic problem original filter theory assumes TEM and coupled line of infinite lenght, in practice dimensions are finite and higher modes(evanesent waves) will propagete thru your structure, so you might need an EM solver, or a good technician for cut and try, usually after first prototype is built you can scale you design in order to be quite close to final result, in designing for such approach leave some room for tuning
To design such filter use CST,QW3D,HFSS, or Mode Matching software, use for starting point Mathaei data, or,PCfilt,Sfilsyn(comb),Parfil or Eagleware M-filter, all of them will do,or make your own Matlab file.

Dear Driends,

Where can I find these books? Wenzel & Horton synthesis, NYJ Book (Mathaei), as well as the italian proffesors paper? Thanks.

Linda

Soft-tuning and optimization combline filters by CST is not easy problem for beginner. There is a very good programme - WASP_NET. If you can find it, you will very pleasure.

To filterman,

I am a beginner of combline design, and working on codes. Would you advise the name or title of the italian proffesors paper ? Thanks.[/quote]

hi
here im also design a interdigital filter by using the mathaei book equations but i need to design combline as well as interdigital filter with round rods is there suggested book for this round rod combline filter if any plz post here or send to mymail id. it is very necessary to me, plz give me the related books for that to read for basics and also to design manually like rectangular bar filters in mathaei book.


thank you
my mail id :hai_maha@yahoo.com

Good initial dimension can be obtained by MYJ's book for narrow band combline filter. However, fine tuning or full-wave optimization should be needed for good results. As for full-wave optimization, the mode-matching method is the most efficient.

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An analytical technique for the synthesis of cascaded N-tuplets cross-coupled resonators microwave filters using matrix rotations

o . how can i get the point?

i have donated you get that paper if you wqant , you have newly joined know so you have to wait upto 14 days after you joined in this forum . then after when you post or reply to any one in this forum so that oyu will get the points

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