[SOLVED] [CST] BandPass Filter Design using Distributed components ??

[kela3kela]

Dear Members,

I would like to design a single Bandpass filter that passes the following frequency bands and blocks all other harmonics:

0.88-1 GHz, 1.75-1.95 GHz, 2.3-2.5 GHz and 5-6 GHz.

Can someone please suggest the methods of desiign such filter using distributed components.
Awaiting replies,

Regards

 

[BradtheRad]

A series LC filter can act as a bandpass. You'll need a separate filter for each individual band.

There are higher order filters which generate more than one node of peak response, and one of them might suit your purpose. However it would be a major challenge to tune its frequency bands precisely to your specs.

 

[kela3kela]

Thankyou for the reply. Any helping document that you can suggest?

 

[BradtheRad]

You can check Wikipedia webpages regarding AC signal filters. Example: Chebyshev, Bessel, elliptical/Cauer, comb, etc.

Probably none of these will come in one simple design to do what you want. You may succeed by combining two or more types.

The comb filter looks as though it might be a good prospect. It is more complicated than a single bandpass filter, however.

https://en.wikipedia.org/wiki/Comb_filter

Sample graph of response:

 

[G4BCH]

Search for antenna diplexer or duplexer designs.
You can buy diplexers/multiplexers for some bands, they are usually either ceramic or cavity types.
I would combine the 1.8/2.4 pair first using a parallel pair of band pass filters, or if the requirement is not too severe maybe a high/low pass combiunation would do. These two are the most difficult to combine easily with low loss.
After that add in the lower frequency with a high/low pass combiner, then the highest one, again with a high low pass combiner. The order of adding the upper and lower frequency is arbitrary.
Others who have experience of this sort of thing will have better ideas, but as far as I can see that is the simplest way of doing it. Doing it all in one single filter is going to be difficult I have seen some multi frequency designs in Micrwaves & RF & Microwave Journal; although interesting in their own right they are rarely useful where good isolation is required.

 

[vfone]

For 2 bands (duplexer) there should be no problem designing such filter, but for 4 bands is practically impossible to make it work having decent performances in all bands simultaneous.
An idea would be to split the design in 2x2 bands, design two duplexers (two for low bands, and two for high bands), and switch/split somehow between these pairs.

 

[kela3kela]

@all Thankyou all for the explanation. It really is a helpful forum