A New Topology for 2D Transmission-Line Array Circuit Simulations

Complex or asymmetrical geometries can be difficult to model using ordinary, 1D, circuit modelling techniques. Simulating these geometries using 2D or 3D FDTD (Finite Difference Time Domain) tools is one solution, but is time consuming to implement, perform, and integrate into a larger circuit. 2D arrays of transmission lines have been used in these situations to give results similar to FDTD but in a much easier and faster way to implement, perform, and integrate into a larger circuit [1]. The existing technique for implementing 2D arrays, the 2D-TLM method [2], is to use a rectangular grid of transmission line elements. One issue with the usual TLM approach is that the impedance and transit time of the individual transmission line elements have to be scaled by the square root of two in order to get the correct behavior. A major problem with this is that the high frequency response of the array is not the same as the 1D representation of a TL element. A new topology for 2D transmission line arrays has been newly developed, known as the Chain Link Fence (CLF) topology. This topology is similar to a rectangular grid that has been rotated by 45 degrees. With the CLF topology, the individual transmission line elements have impedance and transit time values that do not need the square root of two scaling to get the correct response. A major benefit to the CLF topology is that the high frequency response of the array is exactly the same as the 1D representation. The circuit simulation tool, CASTLE [3], compares the TLM and CLF 2D array topologies against the results of FDTD simulations. These results are used to evaluate the CLF as an improved replacement for the grid topology for 2D transmission line array simulations of complex or asymmetrical geometries.