Calibration of directional antennas and limitations in their use

An error due to a directional antenna calibration on an open area test site (OATS) is discussed with an example of a log-periodic (LP) antenna and the substitution method. It is shown that the accuracy of the calibration may be improved by the distance choice, a directional transmitting antenna (TA) use, calibration on a site of reduced reflection coefficient, and the use of calculated or measured correction factors. The approach may be applied to arbitrary directional antennas. Then, limitations in the use of directional antennas for electromagnetic field (EMF) measurements in the conditions of multipath propagation are discussed, and the concept of an omnidirectional set is presented.