If the filter response is complex with multiple cross-couplings it might be hard to find an optimum coupling matrix that fulfills the filter specification. In this case the optimizer can be a useful tool.
To configure your matrix for optimization two things has to be known to the software, the couplings to optimize and the cost function, that is, your goals. Toggling a coupling to be included in the optimization is done in the matrix view and a green dot on the top indicates which couplings are taking part. Goals are defined in the goals view and can be configured to specify rejection levels, return loss and group delay equalization. To prioritize a goal adjust its weighting factor accordingly. The goals view will list the current cost function of each goal.
The optimizer might run into convergence issues and will therefore not find a solution. Convergence is mostly dependent on the goals that has been specified. If there are too few or badly assigned goals the optimizer could be trying to iterate towards a local minimum that is not the global and wanted one. It is up to the designer to specify goals that are not unreasonable. Another issue might be that there are too few couplings included in the optimization that can not support the goals. For instance if one is aiming for an asynchronous response and there’s no cross-coupling and resonator self-coupling to support it the optimization will not converge.
Faster run times
Couplings Designer uses advanced industry standard math operations to solve the unknowns, your couplings. A quasi-newton algorithm performs a number of iterations until it converges. This involves calculating the gradient which is a costly operation. Couplings Designer takes advantage of the latest technology to parallel this operation on all available cores on the processor but the time needed might still be too long deepening on the complexity of the problem. There are numerous ways to reduce the time spent optimizing. Below are a list of what can be done to achieve faster run times.
- Use symmetry where appropriate
- Reduce the number of couplings to optimize
- Minimize the number of frequency points
- Adjust the minimum and maximum physical coupling, external quality and resonator frequency deviation
Back to the Couplings Designer documentation.