PROXIMITY EFFECTS OF ABSORBING BOUNDARY-CONDITIONS ON ANTENNA RADIATION-PATTERNS

Absorbing boundary conditions (ABCs) are needed to surround an antenna and terminate the finite difference time domain spatial domain. The p roximity effects of ABCs which are close to the antenna are investigat ed, and it is shown that specifying the physical distance between an a ntenna and the ABCs is preferable to specifying the number of cells. D istances of about 0.5 lambda have been shown to produce good radiation patterns at all observation angles, but larger distances are necessar y for accurate prediction of antenna gain. The use of the Berenger per fectly matched layer (PML) allows the amount of free space surrounding a structure to be reduced but incurs a computational penalty dependin g on the thickness of the PML.