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Giselle: A Mutually Orthogonal Triple Twin-loop Ground-symmetrical Broadband Receiving Antenna for the HF Band.

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Abstract

This report describes development of a tri-axial mutually orthogonal broadband twin-loop receiving antenna for the HF band. The three twin-loops have been arranged so that they exhibit the same distributed parameters between themselves and ground. The upper frequency limit of the antenna is discussed and a method for extending the low frequency cut-off is presented. The antenna noise factor is calculated from measured data.

Executive Summary

Traditional mutually orthogonal tri-axial loop antennas have distributed parameters to the ground that are not consistent between the three loops. This non-symmetrical characteristic adds complexity to the analysis of signals received from each of the loops. Also, the distributed inductance (L) and capacitance (C) of each loop form a resonant circuit limiting the loop’s usefulness for broadband work. The tri-axial twin-loop antenna design presented in this report has the same distributed parameters to ground on all three loops (ground-symmetrical) easing the analysis burden on the received data. The final version of the antenna presented can cover the complete HF band and is ideal for studying the polarisation of received signals with the view of mitigating HF polarisation fading. The inherent noise produced by the Giselle antenna is less than the expected man-made noise for a quiet rural site; therefore the Giselle antenna can also be used as a compact triaxial polarisation diversity surveillance antenna for the whole of the HF band. It is capable of discriminating between locally transmitted ground wave signals and those transmitted at some distance and received via sky-wave by monitoring for any signs of rotation in the received signal’s polarisation.

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