Halo antenna
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A halo antenna, or halo, is a center-fed 1 /2 wavelength dipole antenna, which has been bent into a circle, with a break directly opposite the feed point. The dipole's ends are close, but do not to
Radiation patterns for a large (left) and a small (right) loop antenna. The light grey square and octagonal rims represent the antenna wires. Colors represent signal strength: magenta and red are "hot" directions of intense signal; blue and indigo are "cold" or low or weak signal; black is no signal. A halo is similar to the right figure, but instead of indigo and black, the center of a halo would be mostly blue: A weak, but non-zero signal.
Car roof-mounted 6 meter halo antenna for mobile amateur radio (by WA8FJW). Note the triple-loop.
Radio frequency
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Radio frequency is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around 20 kHz
Radio-frequency electrical currents are usually carried by specially-designed transmission line such as coaxial cable, as ordinary electrical cables would have high power loss.
Boy allowing the arc from a Tesla coil to strike his hand. Coming in contact with radio frequency arcs as shown here is extremely dangerous and can result in electrocution.