A high-frequency circuit model for the gap excitation of a microstrip line

An equivalent circuit model for a gap voltage source on a microstrip line is developed. The model is valid at high frequencies as long as a single mode propagates on the line and accounts for the reactive nature of the gap as well as the radiative nature of the currents on the line. The model also accounts for the nonunique definition of the characteristic impedance associated with the bound mode at high frequency. The equivalent circuit models the excitation of the bound mode exactly even at high frequencies where standard transmission-line theory is no longer accurate. The frequency behavior of the circuit parameters in the model is shown together with some time-domain results that have been computed by using a very efficient approach based on the proposed circuit model.