Halo antenna

A halo antenna, or halo, is a horizontally polarized, omnidirectional 1/2 wavelength dipole antenna. It is shaped like a loop with a small break on the side of the loop directly opposite the feedpoint, so that the dipole ends do not meet. The antenna is usually one continuous conductor, fed with a gamma match capacitor, although a double-halo system may be utilized, with a larger radiating loop at the top, and a smaller loop on the bottom that is fed directly. The double loop system was the feeding method described in the original patent, with the gamma match feed being more predominate with modern halos. The effective difference is that the double loop is balanced, while a gamma match is unbalanced.

The halo antenna is distinct from the magnetic loop antenna, which is similar, but quite a bit smaller, and the full wave loop, which is larger and in which the element is a complete loop.

US 2324462, "High Frequency Antenna System", issued July 14, 1943 

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