A STUDY OF TRANSIENT RADIATION FROM THE WU-KING RESISTIVE MONOPOLE - FDTD ANALYSIS AND EXPERIMENTAL MEASUREMENTS

The cylindrical monopole antenna with a continuous resistive loading is considered as a radiator for temporally short, broad-bandwidth pulses. Specifically, the variation of the resistance used along the monopole is one proposed by Wu and King (Wu-King profile). This antenna is analyzed by the finite-difference time-domain (FDTD) method utilizing a new, efficient technique for handling the thin-walled, conducting tube that forms the resistance. The electromagnetic field in the space surrounding the antenna is determined as a function of time, and quantities useful for describing the performance of the antenna are then calculated from these results: the reflected voltage in the transmission line, the surface charge density on the antenna, and the time-varying field in the far zone. Graphical displays of these results are used to give new insight into the physical processes for transient radiation from this antenna. An experimental model is constructed using a discretized version of the Wu-King profile formed from a set of precision, high-frequency resistors. The fine details of these resistors are accurately included in the FDTD analysis. Measurements of both the reflected voltage in the feed line and the time-varying radiated field are in excellent agreement with the theoretical calculations.