Section: New Results

Sensitivities of Electrical Parameters with respect to physical parameters

Participants : Matthias Caenepeel, Martine Olivi, Fabien Seyfert.

This work was conducted in collaboration with Yves Rolain (VUB, Brussels, Belgium). The goal is to automatize and improve our computer-aided tuning (CAT) method for coupled-resonator microwave synthesis, which is based on rational approximation and circuit extraction as explained before. The novelty here lies with estimating the Jacobian of the function that relates the physical filter design parameters to the extracted coupling parameters. Lately commercial full-wave electromagnetic (EM) simulators provide the adjoint sensitivities of the S-parameters with respect to the geometrical parameters. This information allows us for an efficient estimation of the Jacobian since it no longer requires finite difference based evaluation. Our tuning method first extracts the physically implemented coupling matrix, and then estimates the corresponding Jacobian. Next it compares the extracted coupling matrix to the target coupling matrix (golden goal). Using the difference between the coupling matrices and the pseudo-inverse of the estimated Jacobian, a correction that brings the design parameters closer to the golden goal is obtained. This process is repeated iteratively until the correction becomes sufficiently small with respect to a user-specified goal. In the case of coupling structures with multiple solutions, the Jacobian is calculated for each admissible solution. This paper presents a criterion to identify the physical solution among the different possibilities. The CAT method has been applied to the design of a cascaded triplet (CT) filter implemented in a microstrip technology. This filter is a well-known examples of a non-canonical coupling structure. See [24] for details.