Folded Waveguide Circuit Optimizations using Christineid

Abstract

Summary form only given. Calabazas Creek Research (CCR) and North Carolina State University implemented several novel features into the optimization capabilities of the large signal traveling wave tube (TWT) interaction code, Christine1D. The internal optimization capabilities of Christine1D are currently limited to the design of helix circuits. The present scheme varies a geometric parameter, such as the helix pitch, and calculates the corresponding cold-test characteristics, including phase velocity and interaction impedance, using an analytical sheath or tape helix model. To expand the flexibility of the code to other types of slow wave structures, we have introduced the option to define the dependence of these cold-test characteristics manually. These characteristics, and their dependence on variations to geometric parameters as would be implemented in a phase velocity taper, can be very accurately determined using a three-dimensional code such as Microwave Studio. Then, the user defines this dependence in Christine1D through curve fitting equations. Currently, Christine1D employs a modified steepest descent method to carry out the optimization process. We have used both the Nelder-Mead and the DIRECT algorithms. Optimization results will be presented showing a significant improvement over the currently implemented steepest descent model. Lastly, Christine1D has a limited number of design goal functions. Several new goal functions were introduced where the user has the option of using them simultaneously with weighting schemes depending on the application. These goal functions were used to design a W-band folded waveguide TWT circuit according to the specifications supplied by the customer. Results for several goal function combinations will be presented.