A SPICE model for multiconductor transmission lines excited by an incident electromagnetic field

Abstract

This paper describes a SPICE model that may be used for predicting the time-domain or frequency-domain voltages and currents induced at the terminations of a multiconductor transmission line (MTL) by an incident electromagnetic held. Explicit results for the entries in the SPICE circuit model are obtained for an incident uniform plane wave that may represent sources such as radio and television transmitters, radars, lightning, etc. The result relies on the transformation of the MTL equations into uncoupled modal lines by similarity transformations. The entries in the similarity transformations are provided for lossless lines. The model is implemented using controlled sources to implement the modal transformations and delay lines to implement the modal lines. If the model is implemented as a SPICE subcircuit model, the time-domain form of the incident field can be implemented as a source external to that subcircuit model so that changes in the line responses due to changes In the incident field waveform can be simulated without changing the subcircuit model. In order to avoid negative line delays, the result is restricted to incident waves having components of the propagation vector in the positive direction along the line. This restriction can be removed by simply reversing the line. The paramount advantages of the model are that both time-domain and frequency-domain results can be easily obtained with the existing SPICE code, and nonlinear loads, such as transistors and digital devices, as well as dynamic loads, such as inductors and capacitors, may be easily incorporated using the existing elements in the SPICE code. Predicted results for MTL's using the method are compared to those of the time-domain to frequency-domain transformation and finite difference-time-domain (FDTD) methods.