Parameterization of a transient electromagnetic facility and test antennas from transient data

The Lawrence Livermore National Laboratory is characterizing antennas in their environments from transient reflectometry and scatter data taken on an Electromagnetic Transient Facility (EMTF). This paper describes the linear-system ARMAX modeling of the entire EMTF and derivation of the frequency-domain equivalent circuit of an antenna at its load port. The EMTF is decomposed into blocks and model identification of each is achieved by data preprocessing, model-order testing, parameter estimation, prediction error tests for fit validation, and finally ensemble data tests on a well-understood electromagnetic dipole for overall EMTF model validation. Various special ARMAX methods for modeling the equivalent circuit are compared, with emphasis on a special nonlinear least-squares algorithm. Data processing rules are given. Results for a 30 cm monopole antenna are presented. Problems are summarized in the conclusions.