Loop antennas in the 3-30 MHz band

Abstract

The loop antenna, in common use in the 3-30 MHz band, was reassessed in a previous paper in which it was considered as a folded dipole, with suggested theoretical advantages. This paper demonstrates that the two lowest-order modes which exist in small loop antennas correspond to the true loop, otherwise known as the magnetic dipole (zero-order mode) and the folded dipole (first-order mode), and shows their relative amplitudes in a typical case over representative frequency range. The relative amplitudes of the radiated fields resulting from the modes are also described. At the frequency at which the loop circumference is one eighth wavelength, the loop mode produces 11 dB more radiated field than the folded-dipole mode. The latter becomes relatively more significant at the rate of 6 dB per octave in the frequency range of interest.