Parallel coupled line Band pass filter

Hey

I am designing parallel coupled line band pass filter, and I want to know what is the substrate usually used in this design?

One more thing, how much should be (ideal) S-parameter S11, S22, S21, S12 within the frequency bandwidth required?



Thank you

Mabrok, To begin with, read filter fundamentals from Textbook such as Microwave Engineering by Pozar. You will see how the S-parameters of filters look like. Also, if your project is an academic one, use a cheap FR4 material for your first design.

Later, you may go through more thorough book such as "Microstrip Filters for RF / Microwave Applications by Hong/ Lancaster".

Choose a permittivity where length of resonators fits your available board size. Higher permittivity results in smaller pyhsical size.
Look for small tolerances in permittivity if your filter is narrow band.
Look for small dielectric loss tanget, because that reduces insertion loss.

For the substrate height, look at gap width. Thinner substrates result in narrower gaps, which might be difficult for manufacturing tolerances.

Thank you for your advice