Contrawound antenna

Details Contrawound antenna Contrawound antenna

2000-08-15

2002-08-20

Le, Hoanganh (Department: 2821)

Communications: radio wave antennas

Antennas

High frequency type loops

C343S867000, C343S870000

Reexamination Certificate

active

06437751

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to transmitting and receiving antennas, and, in particular, to antennas employing contrawound windings.
2. Background Information
U.S. Pat. Nos. 5,442,369; and 6,028,558, which are incorporated by reference herein, disclose Contrawound Toroidal Helical Antennas (CTHAs).
Referring to
FIG. 1
, one type of CTHA
2
, for example, employs a toroidal surface and two contrawound helical windings
4
,
6
, which are fed with opposite currents in order that the magnetic flux of each helix reinforces the loop magnetic flux. This additive effect of the two helices may produce a stronger magnetic flux than a single toroidal helix, but the magnetic flux is not uniform. The effect can approach uniform currents for an electrically small CTHA, but suffers poor efficiency.
U.S. Pat. Nos. 4,622,558; and 4,751,515 discuss certain aspects of toroidal antennas as a technique for creating a compact antenna by replacing the conventional linear antenna with a self resonant structure that produces vertically polarized radiation that will propagate with lower losses when propagating over the earth. These patents initially discuss a monofilar toroidal helix as a building block for more complex directional antennas. Those antennas may include multiple conducting paths fed with signals whose relative phase is controlled either with external passive circuits or due to specific self resonant characteristics. In a general sense, the patents discuss the use of so called contrawound toroidal windings to provide vertical polarization. The contrawound toroidal windings discussed in these patents are of an unusual design, having only two terminals, as described in the reference Birdsall, C. K., and Everhart, T. E., “Modified Contra-Wound Helix Circuits for High-Power Traveling Wave Tubes”,
IRE Transactions on Electron Devices,
October, 1956, p. 190. The patents point out the distinctions between the magnetic and electric fields/currents and extrapolate that by physically superimposing two monofilar circuits, which are contrawound with respect to one another on a toroid, a vertically polarized antenna can be created using a two port signal input. The basis for the design is the linear helix, the design equations for which were originally developed by Kandoian & Sichak in 1953.
U.S. Pat. No. 5,654,723 discloses antennas having various geometric shapes, such as a sphere. For example, if a sphere is small with respect to wavelength, then the current distribution is uniform. This provides the benefit of a spherical radiation pattern, which approaches the radiation pattern of an ideal isotropic radiator or point source, in order to project energy equally in all directions. Other geometric shapes may provide similar benefits. Contrawound windings are employed to cancel electric fields and leave a magnetic loop current. Thus, different modes of operation of a CTHA may be induced by varying the antennas' geometric properties.
U.S. Pat. No. 5,654,723 also discloses CTHA antennas employed in combination with a reflector.
U.S. Pat. Nos. 5,734,353 and 5,952,978 disclose CTHAs having feed mechanisms including series-parallel impedance matching network (FIG.
59
), electric current conduction employing a magnetic loop signal coupler (FIG.
60
), and magnetic induction to couple a signal, applied to terminals, from a primary coil directly to a generalized contrawound toroidal helix (FIG.
61
).
It is known to employ a simple linear helix which is designed to end-fire (i.e., radiate off the end of the helix predominately) or broadside fire.
FIG. 2
shows the currents in the two helices of
FIG. 1
at the half wavelength resonance as predicted by the Los Alamos National Laboratory's Numerical Electromagnetics Code (NEC). These non-uniform currents, in turn, produce non-uniform magnetic fields.
As shown in
FIG. 3
, the exemplary NEC simulation provides a 3D-radiation (i.e., &thgr; plus &phgr;) pattern
10
having two dimples (only one dimple
12
is shown). This pattern about the origin
14
is considerably different from the radiation pattern of a dipole. While not all CTHA antennas have as pronounced a dimple as the one shown in
FIG. 3
, those antennas all share the characteristic of near isotropic radiation (i.e., there is no overhead null).
Although the prior art shows various antenna structures and feeds, there is room for improvement.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, an electromagnetic antenna comprises: a multiply connected surface; first and second insulated conductors, with the first insulated conductor extending around and over the multiply connected surface with a first pitch or winding sense from a first node to a second node, and with the second insulated conductor also extending around and over the multiply connected surface with a second pitch or winding sense, which is opposite from the first pitch or winding sense, from a third node to a fourth node, in order that the first and second insulated conductors are contrawound relative to each other around and over the multiply connected surface; and first and second signal terminals, wherein the first node is electrically connected to the fourth node, and the first and second signal terminals are electrically connected to the second and third nodes, respectively.
In accordance with another aspect of the invention, an electromagnetic antenna comprises: a multiply connected surface; first and second insulated conductors, with the first insulated conductor extending around and over the multiply connected surface with a first pitch or winding sense from a first node to a second node, and with the second insulated conductor also extending around and over the multiply connected surface with a second pitch or winding sense, which is opposite from the first pitch or winding sense, from a third node to a fourth node, in order that the first and second insulated conductors are contrawound relative to each other around and over the multiply connected surface; and first and second signal terminals, wherein the third node is electrically connected to the fourth node, and the first and second signal terminals are electrically connected to the first and second nodes, respectively.
In accordance with a further aspect of the invention, an electromagnetic antenna comprises: a multiply connected surface; first and second insulated conductors, with the first insulated conductor extending around and over the multiply connected surface with a first pitch or winding sense from a first node to a second node, and with the second insulated conductor also extending around and over the multiply connected surface with a second pitch or winding sense, which is opposite from the first pitch or winding sense, from a third node to a fourth node, in order that the first and second insulated conductors are contrawound relative to each other around and over the multiply connected surface; and first and second signal terminals, wherein the second node is electrically connected to the third node and the fourth node, and the first and second signal terminals are electrically connected to: (a) the second, third and fourth nodes, and (b) the first node, respectively.
In accordance with another aspect of the invention, an electromagnetic antenna comprises: a multiply connected surface; first and second insulated conductors, with the first insulated conductor extending around and over the multiply connected surface with a first pitch or winding sense from a first node to a second node, and with the second insulated conductor also extending around and over the multiply connected surface with a second pitch or winding sense, which is opposite from the first pitch or winding sense, from a third node to a fourth node, in order that the first and second insulated conductors are contrawound relative to each other around and over the multiply connected surface; and first and second signal terminals, wherein the first node is electrically connected to the third node, the second node is elec

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