Resonator Cavity coupled Narrow band Microwave Filter

Hello,

How we can design the Narrowband Microwave bandpass filter using Cavity Resonator Filter coupled with small irises ? How we can decide the size and type of iris that can be suitable for our filter?

Is there any limitation for using the number of iris structure that can use for one filter ? How we can decide that either i can use circular or rectangular iris in my structure ?

can we combine circular and rectangular iris in one waveguide filter ? How basically they react ?

What is the center frequency and passband edges? What are the stop band edges and how much attenuation is required at the stop band frequency?

Frequency range - 12-18 GHz
Bandwidth ~20 MHz

I think the best sources for your question are going to be from Microstrip Filters for RF / Microwave Applications by Hong and Lancaster or Microwave Filters for Communication Systems by Cameron. Both of these methods describe synthesis of filters using the coupling matrix, which is a very handy tool for making filters using coupled cavities. Changing the size of the iris will change the coupling between the cavities, thus affecting filter characteristics. I'm not sure what the differences are in circular and rectangular irises, I suspect that's mainly a manufacturing concern.

Thank you for your valuable suggestions as per my knowledge An iris which reduces the width of a rectangular waveguide has an equivalent circuit of a shunt inductance, whereas one which restricts the height is equivalent to a shunt capacitance. An iris which restricts both directions is equivalent to a parallel LC resonant circuit. A series LC circuit can be formed by spacing the conducting portion of the iris away from the walls of the waveguide. Narrowband filters frequently use irises with small holes. These are always inductive regardless of the shape of the hole or its position on the iris.