Magnetic loop antennas Roger reini, kd8cse febrUary 2017

Two types of loop antennas Large Loop – size ison the order of a wavelength (quad, delta) Small Loop – size is much smaller than a wavelength This presentation will deal with SMALL loop antennas

Magnetic loop antenna? Alternate term for the small loop antenna Refers to the fact that they respond better to the magnetic component of an EM wave and transmit a large magnetic component in the extreme near field (< 0.1 wavelength distance) In far field (>1 wavelength), the EM waves naturally have E and M components

Antenna basics Diagram of a small loop antenna Equivalent Circuit

ANTENNA PARAMETERS Pick any TWO of the following: Small size (in terms of wavelength) Efficiency Bandwidth Magnetic loop antennas are small and tend to be efficient Their bandwidth, therefore, is very narrow

Tuning capacitor For maintaining low losses, and for handling large voltages (kV), a vacuum variable capacitor is preferred

antenna performance When vertically polarized, nulls are perpendicular to face of loop Strongest directionality in plane of loop Easy to null out QRM/QRN

Antenna performance (cont’d) When horizontally polarized, antenna acts like a vertical antenna Omnidirectional radiation pattern Does not require a ground plane

Some benefits Antenna is low profile, so it is easily concealed Stealth antenna built into a table: http://www.alexloop.com/artigo15.html

references http://www.aa5tb.com/loop.html Burger and Dvorsky, Magnetic Loop Antenna: Slightly Different Each Time, Ostrova, 2015 Leigh Turner, VK5KLT, “An Overview of the Underestimated Magnetic Loop Antenna,) http://www.brisdance.com/vk4amz/files/Download/UnderMagLoop.pdf