Finite-difference time-domain of HF antennas

Although there has been extensive research and application of the finite-difference time-domain (FDTD) method to electromagnetic scattering and penetration problems, only recently has FDTD been used to predict the radiation characteristics of antennas. The FDTD method has not been applied to low frequency or electrically small radiating structures. The development of higher-order absorbing boundary conditions (ABC) has allowed the use of very small cell sizes in the FDTD computational space by placing the absorbing boundaries closer than the traditional one wavelength from the scatterer or radiating structure. In this study, the FDTD method with higher-order absorbing boundary conditions is used to model and predict the far-field radiation of electrically short antennas. Results are presented and compared with measurement for HF loop or "towel bar" and inverted-L antenna elements used at 10 MHz mounted on a helicopter-like body, a square cylinder. The computed radiation patterns compare well with measurements. An FDTD cell size of /spl lambda//120 was used to model the smallest dimension of the problem, the height of the antenna.