Subtraction of Discontinuity Susceptance for WIPL-D Source Modeling

Abstract

WIPL-D does not include a provision for a direct specification of a coaxial line excitation of patch antennas in terms of the incident dominant TEM mode. Instead, such an excitation is approximated by a voltage generator in series with a thin wire, one end of which is connected to the inner conductor of the coax and the other end to a flat shorting cap joined to the outer conductor. The transition from the diameter of the inner conductor to the diameter of the wire gives rise to a spurious capacitive shunt susceptance leading to an error in the calculated antenna input impedance. It is shown that this susceptance can have a significant effect on the WIPL-D calculations of the return loss of narrow band patch antennas. A computational technique is presented for neutralizing this modeling deficiency.