An improved method for determining normalized site attenuation using log periodic dipole arrays

A normalized site attenuation (NSA) measurement, made using LPDA free-space antenna factors (AF) as specified in ANSI C63.4, has up to 3 dB of systematic errors due to limitations in the current theory. The ANSI model fails to account for the log periodic antenna's radiation pattern and its active phase center position, which were shown to be the dominant effects causing these errors. An enhanced theoretical model is introduced in this paper to take these two effects into account. In the enhanced model, antenna radiation patterns and active phase center positions are assumed to be unknown. At each frequency, the unknowns are solved by fitting the theoretical magnitude or phase response to a measured antenna response taken at different heights. The complex fit NSA (CFNSA) is then obtained by including the varied phase center and radiation pattern of the antennas under test. It is shown that the CFNSA model reduces the systematic errors in the current NSA to less than a dB.