Dear Tashin,

The following paper focuses on the design of dual- and tripleband filters by employing the coupling matrix and the optimization of its entries. One of the major advantages of this approach is that topologies and certain coupling elements can be controlled from the onset. The basic design steps are shown here at the example of a triple-band filter with six resonators and four transmission zeros, each two of which are located between adjacent passbands. The individual passbands are centered at 2.65, 3, and 3.35 GHz, and more than 50-MHz bandwidth is to be retained in each of the bands. The conclusions emerged from this paper is that the coupling-matrix design procedure for dual- and triplepassband filters presents a viable alternative to current multiband filter design techniques. The method is flexible, not restricted to certain filter types or topologies, and is capable of including higher order mode effects. The coupling scheme and limitations for the coupling coefficients can be enforced during the design. The feasibility of this technique is demonstrated for filter configurations in microstrip and waveguide technology. The designs are verified by measurements and a number of different full-wave codes.

To view the full publication, please use the following link:

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.725.5765&rep=rep1&type=pdf

Hoping this will be helpful,

Rafik

thank you for the reply, I have read this paper and some other Amari's works but papers which are appropriate for wideband filters don't have all possible coupling between resonators.

 I am also looking for coupling matrix codes which have been used for extraction of coupling matrix in these papers. Can anyone share Matlab codes of coupling matrix? Or maybe some section of codes?

Read chapter 8 of following book.

Hong J.-S. and Lancaster M. J. ‘Microstrip filters for RF/microwave applications’ John Wiley and Sons Inc. 2001 ISBN 0-471-38877-7