Efficient estimation of adjoint‐variable S ‐parameter sensitivities with time domain TLM

We present a novel algorithm for efficient estimation of S ‐parameter sensitivities with the time‐domain transmission line modelling (TLM) method. The original electromagnetic structure is simulated using TLM to obtain the S ‐parameters in the desired frequency band. For each port, an adjoint TLM simulation that runs backward in time is derived and solved. The sensitivities of the S ‐parameters in the desired frequency band are estimated using only the original and adjoint simulations. For a structure with N p ports and n designable parameters, our approach requires only N p additional simulations regardless of n . This can be easily contrasted with the 2 nN p additional simulations required by the central difference approximation. Our algorithm is illustrated through the estimation of S ‐parameter sensitivities with respect to the dimensions of waveguide discontinuities. Very good match is obtained between our sensitivity estimates and those obtained using central difference approximation. Copyright © 2005 John Wiley & Sons, Ltd.