Alford loop

Vertical magnetic Alford loop

In free space

As seen with the medium size loop, we don’t want the dipole mode. We only want the loop (transmission line) mode. That is just what is accomplished in the Alford loop. Originally the Alford(/K6STI) loop is used as a horizontal loop.

In the Alford loop the loop is symmetrical fed on two opposite corners. Though relative large compared to the wavelength the Alford loop behaves like a very small loop.

Originally (as with the K6STI loop also) an open line feeder is used. By adapting a slightly different layout the resulting capacitance can be reduced. This shifts the resonance frequency back up to about the same frequency as shown by the normal loop. When the circumference is about 0.5´l the loop resonates.

The resulting radiation pattern in the YZ-plane (horizontal polarization) shows very deep nulls all the way:

Picture of the Alford loop (130kB)

Last update: September 24, 2006