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Messages - Bob W0BNC

Antennas / Re: Magnetic antenna query
March 16, 2021, 02:14:16 PM
Quote from: daedalus on November 06, 2019, 11:38:52 PMHow does a magnetic loop "know" it is to pick up magnetic waves and not electric , probably something very simple and if so apologise for asking !

This is a paragraph taken from Leigh Turner's (VK5KLT) most outstanding white paper entitled "An Overview of the Underestimated Magnetic Loop HF Antenna", a must-read 33 page document on magnetic loops that can be quickly found on Google:

Current flow through the loop's radiation resistance results in RF power being converted / transmuted into electromagnetic radiation.  A propagating radio wave transporting power in the Poynting (*) vector must comprise of both magnetic (H) and electric (E) field components in a prescribed ratio in order for it to exist.  In the case of the STL, a strong magnetic field is generated by passing a substantial RF current through the loop conductor and this magnetic field in turn generates a corresponding electric field in space, thus providing the two essential and inextricably linked E and H component elements.  This is where the term "magnetic loop" antenna originates.  The radiation resistance of a small loop antenna is proportional to the square of the peak magnetic dipole moment of the antenna.  This dipole moment is roughly the product of the peak current times the area of the magnetic loop antenna.  Reciprocity applies in the antenna receiving sense.

(*) – Poynting vector represents the directional energy flux of the electromagnetic field.