An improved adjoint method for design of microwave devices with 3D finite elements /

A numerical method is described for determining the derivatives of the scattering parameters of an arbitrary 3D microwave device with respect to changes in model geometry. The new technique is based on the adjoint variable method as applied to finite element analysis, but does not require the separate calculation of an adjoint solution. The new technique is applied to the optimization of the design of microwave components, using a derivative-based, quasi-Newton method.The derivatives of the scattering parameters of three devices are computed and compared to analytical or finite difference values. The agreement is very good. The three devices are: a length of short-circuited waveguide, an E-plane miter-bend, and a waveguide transformer.The short-circuited waveguide length is then optimized to achieve a specified phase of the reflection coefficient. The miter-bend and the transformer are optimized for minimum return loss. All optimizations reached the (local) optimum solution after only 4--12 computations of the field