HF active loop antenna response

The purpose of this paper is to present the phase and amplitude characteristics of an active loop antenna, which can be easily fitted into a polarization diversity sensor built with two crossed loops. We shall first consider the determination of the intrinsic complex effective height of the loop, taking into account the propagation effects of an incoming wave from the ionosphere. The antenna aerials are connected to preamplifiers which increase effective height, and also match them to the rest of the measurement system. In a second part, we show how the complex effective height is modified after passage through the preamplifier. These developments are illustrated by experimental measurements which take into account of the phase and amplitude of several incoming HF skywaves, identified by their direction of arrival and polarization. Finally, the performances in terms of antenna factor, of a small active circular loop antenna (radius 0.65 meters) are compared with those of an eight meter high passive biconical antenna.