The microwave cavity filter, which is operated by coaxial resonators with high Q-factors above 4 000, has high power and high performance.
Coupling matrix synthesis is the most important step in the design of microwave filters. This is because coupling matrix is the most critical in mapping the theoretical filter characteristic polynomial to the parameters of a physical filter model.
The coupling matrix of a microwave cavity filter is not a feasible topology, so it must be reconstructed by performing a similarity transformation. The reconstruction of coupling matrix using the rotation matrix is not suitable for lossy filter design and there are several problems in reconstructing the coupling matrix, which necessitates different approaches.
Kim Chol Jin, a researcher at the Faculty of Communication, proposed using hyperbolic reflection matrix in the coupling matrix synthesis to design a microwave cavity filter for use in mobile station remote radio units.
First, he synthesized an orthogonal matrix that can simplify the complex coupling matrix obtained in the design of a microwave filter with loss considerations. Then, he solved the problem of code control of cross-coupling arising in reconstructing a general coupling matrix.
The experimental results show that a coupling matrix is reconstructed to have desired topology and that a hyperbolic reflection matrix can reconstruct a complex coupling matrix.