Toroidal antenna

DETAILED DESCRIPTION In the present invention electrically small, yet self-resonant and, therefore, efficient, electromagnetic structures are disclosed.
These structures may be used as antennas or waveguide probes.
By employing a slow wave structure including an electromagnetically closed path and by operating the structure at one of the frequencies at which an inhibited-velocity standing wave is established along the closed path, a small, yet self-resonant, i.
e.
, efficient, antenna or probe may be achieved.
These structures are not only self-resonant (i.
e.
, have a nonreactive input impedance), but also possess relatively large radiation resistances.
A particularly useful embodiment of the inventive structure, and one that may be used as a building block to build more complex structures, includes a toroidal, helical electrically conducting path.
In a simple case, the structure has a single conductive path, such as a copper wire or other electrical conductor, disposed on the surface of a torus in uniformly spaced turns.
The axis of the helical path lies on a circle which is described by the major radius of the torus.
(A toroidal surface is generated by the rotation of a closed planar figure about a rotational axis lying outside the figure.
When that figure is a circle, the surface generated is a torus.
For a torus, the distance between the rotational axis and the center of the rotated circle is the torus' major radius.
) When the conducting path on the toroidal surface is electrically excited in a pre-selected frequency range, a pair of slow electromagnetic waves, i.
e.
, ones with propagation velocities less than the speed of light, propagates along the path.
At the resonance frequencies of the toroidal path, an inhibited-velocity standing wave is established along the electromagnetically-closed path, which in this elementary example is approximately equal to the circumference of the torus.
Because of the inhibited-velocity propagation, i.
e.
, the slow wave effects imparted by the structure, the standing wave that is established has an inhibited or guide wavelength