Background Information U. S. Patent Nos. 5,442,369; and 6,028,558, which are incorporated by reference herein, disclose Contrawound Toroidal Helical Antennas (CTHAs).

Referring to Figure 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. Patent 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 charactristics. In a general sense, the patents discuss the use of so called contrawound toridal wndings 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. Patent 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.

Patent 5,654,723 also discloses CTHA antennas employed in combination with a reflector.

U. S. Patent Nos. 5,734,353 and 5,952,978 disclose CTHAs having feed mechanisms including series-parallel impedance matching network (Figure 59), electric current conduction employing a magnetic loop signal coupler (Figure 60), and magnetic induction to couple a signal, applied to terminals, from a primary coil directly to a generalized contrawound toroidal helix (Figure 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.

Figure 2 shows the currents in the two helices of Figure 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 Figure 3, the exemplary NEC simulation provides a 3D- radiation (i. e., 0 plus () 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 Figure 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 electrically connected to the fourth node, and the first and second signal terminals are electrically connected to: (a) the first and third nodes, and (b) the second and fourth 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 first node is electrically connected to the second node, the third node is electrically connected to the fourth node, and the first and second signal terminals are electrically connected to: (a) the first and second nodes, and (b) the third and fourth 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 at least one of the nodes is open.

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 first, third and fourth nodes are electrically connected, wherein one of the first and second signal terminals is electrically connected to the second

node, and wherein the other of the first and second signal terminals is structured for connection to a cooperative antenna structure.

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; first and second signal terminals; and a cooperative antenna structure, wherein one of the first and second signal terminals is electrically connected to at least one of the nodes, and wherein the other of the first and second signal terminals is electrically connected to the cooperative antenna structure.

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; first and second signal terminals structured for transmitting or receiving an antenna signal ; and means for coupling the antenna signal to or from the first and second insulated conductors, wherein at least one of the nodes is open.

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; first and second signal terminals structured for transmitting or receiving an antenna signal; and means for coupling the antenna signal to or from the first and second insulated conductors, wherein the first node is electrically connected to the second node, the third node is electrically connected to the fourth node, and the first and second nodes are electrically connected to the third and fourth nodes.

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; first and second signal terminals structured for transmitting or receiving an antenna signal; and means for coupling the antenna signal to or from the first and second insulated conductors, wherein the first node is electrically connected to the third node, and the second node is electrically connected to the fourth node.

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; first and second signal terminals structured for transmitting or receiving an antenna signal; and a shielded loop, proximate the multiply connected surface, without passing completely around the surface, connected to the signal terminals and coupling the antenna signal to or from the first and second insulated conductors, wherein the first node is electrically connected to the fourth node, and the second node is electrically connected to the third node.

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; first and second signal terminals structured for transmitting or receiving an antenna signal; and means for coupling the antenna signal to or from the first and second insulated conductors, wherein the first node is electrically connected to the second node, and the third node is electrically connected to the fourth node.

BRIEF DESCRIPTION OF THE DRAWINGS A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which : Figure 1 is an isometric view of two helical windings in a Contrawound Toroidal Helical Antenna (CTHA) structure; Figure 2 is a plot, which shows the current distribution of the CTHA of Figure 1 at a self-resonance ;

Figure 3 is a plot of the radiation pattern of the CTHA of Figure 1 for the current distribution of Figure 2; Figures 4A-4B are wiring diagrams for CTHAs having polar and equatorial crossings, respectively; Figures 5A-5D are views of various CTHA feeds, which employ two feed lines in accordance with embodiments of the present invention; Figures 5E and 5F are views of various CTHA feeds which employ two feed lines; Figures 5G-5M are views of various CTHA feeds, which employ two feed lines in accordance with embodiments of the present invention; Figures 6A-6M are views of various CTHA feeds, which employ only one direct feed connection in accordance with embodiments of the present invention; Figures 7A-7G and 71 are views of various CTHA feeds, which employ no direct feed connection in accordance with embodiments of the present invention; Figure 7H is a view of a CTHA feed, which employs no direct feed connection; Figures 8-15 are plots of the impedance spectrums for the feeds of Figures 5A-5H ; Figure 16 is a plot of calculated resonant frequencies for a CTHA having the feeds of Figures 5A-5H ; Figure 17 is a plot of real impedance at various resonances for the feeds of Figures 5A-5H ; Figure 18 is a plot of maximum azimuthal gains for the feeds of Figures 5A-5H at the respective first resonances; Figure 19 is a plot of average azimuthal gains for the feeds of Figures 5A-5H at the respective first resonances; Figure 20 is a plot of average azimuthal gains for the feeds of Figures 5A-5H at the respective first resonances as shown at the frequency of those resonances;

Figures 21A-21C through 28A-28C are far-field plots oftheta- polarized gain (Figures 21A-28A), phi-polarized gain (Figures 21B-28B), and total gain (Figures 21C-28C) for the feeds of Figures 5A-5H, respectively, at the respective first resonances; Figure 29 is an azimuth cut of theta-polarized gain versus phi-degrees at each of the first resonances for the feeds of Figures 5A-5H ; Figure 30 is an azimuth cut of phi-polarized gain versus phi-degrees at each of the first resonances for the feeds of Figures 5A-5H ; Figure 31 is an azimuth cut of total gain versus phi-degrees at each of the first resonances for the feeds of Figures 5A-5H ; Figure 32 is a plot of total gain versus frequency averaged over the entire far-field sphere in order to approximate efficiency ; Figure 33 is a plot of theta-polarized gain versus frequency averaged over the azimuth cut; Figure 34 is a plot of phi-polarized gain versus frequency averaged over the azimuth cut; Figure 35 is a plot of sphericity theta-polarized gain versus frequency for the feeds of Figures 5A-5H over the entire far-field sphere; Figure 36 is a plot of sphericity phi-polarized gain versus frequency for the feeds of Figures 5A-5H over the entire far-field sphere; Figure 37 is a plot of sphericity total gain versus frequency for the feeds of Figures 5A-5H over the entire far-field sphere; Figures 38A-38C are far-field plots oftheta-polarized gain, phi- polarized gain, and total gain, respectively, for a vertical loop; Figures 39A-39C are far-field plots of theta-polarized gain, phi- polarized gain, and total gain, respectively, for a horizontal loop ; Figures 40A-40B are plots of current versus distance along the conductors in the two contrawound windings for the feeds of Figures 5A-5H ; Figure 41 is a block diagram in schematic form of an electromagnetic antenna employing a ground plane;

Figure 42 is a block diagram in schematic form of an electromagnetic antenna employing a reflector; Figure 43 is a block diagram in schematic form of an electromagnetic antenna employing a second contrawound toroidal helical antenna; Figure 44 is a block diagram in schematic form of an electromagnetic antenna in which the antenna signal is capacitively coupled to the contrawound insulated conductors; Figure 45 is a block diagram in schematic form of an electromagnetic antenna in which signal terminals provide antenna coupling of a passive element in an array; Figure 46 is a block diagram in schematic form of an electromagnetic antenna in which signal terminals provide antenna coupling of passive elements in an array; Figure 47 is a block diagram in schematic form of an electromagnetic antenna in which the antenna signal is inductively or magnetically coupled to the contrawound insulated conductors; and Figures 48 and 49 are cross-sectional views of alternative multiply connected surfaces.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As employed herein the term"multiply connected surface"shall expressly include, but not be limited to: (a) any toroidal surface, such as a preferred toroid form having its major radius greater than or equal to its minor radius, or a toroid form having its major radius less than its minor radius (see, for example, Patent 5,654,723); (b) other surfaces formed by rotating and transforming a plane closed curve or polygon having a plurality of different radii about an axis lying on its plane; and (c) still other surfaces, such as surfaces like those of a washer or nut such as a hex nut, formed from a generally planar material in order to define, with respect to its plane, an inside circumference greater than zero and an outside circumference greater than zero, with the outside and inside circumferences being either a plane closed curve and/or a polygon. Furthermore, such multiply connected surfaces may include

surfaces formed by an air core or formed on parallel layers of a printed circuit board antenna.

Many factors must be considered when designing an antenna: the efficiency, the input impedance, the far-field radiation pattern, the polarization of the radiated energy, and the size and shape of the antenna. Different applications may stress different factors in the design process.

In accordance with an important aspect of the present invention, the feed of the antenna gives the antenna designer an additional parameter to vary in trying to meet application-specific requirements.

The strength of the prior art CTHA lies in its relatively low profile, which yields a nearly isotropic radiation pattern of predominately theta-polarized radiation. Not all communication tasks require this combination of characteristics.

Thus, new characteristics may be developed by varying antenna parameters, including the feed.

For example, an antenna application might need phi-polarized radiation, or it may be geometrically constrained into a vertical position but still need theta-polarized radiation.

As another example, even when a CTHA is in a vertical position (e. g., in a lollipop mode, in the manner of a coin standing on its edge, with the plane of the major circumference being perpendicular to the ground), it is still a compact device that is smaller than conventional antennas, such as a vertical loop antenna.

In an application where cost is the dominating factor, such as a disposable smart card, the need to obtain a 50 ohm input impedance, without the use of costly discrete components in a matching network, may cause an antenna designer to sacrifice uniform radiation pattern or antenna efficiency in the quest for a naturally matched antenna. For example, this case might occur for an in-room communication link connecting a portable device to a network via a wireless link.

A significant variety may be introduced both to input impedance characteristics and to the polarization and radiation pattern of an antenna through the feed selections disclosed herein.

An alternative method of feeding a CTHA includes the use of inductive loops. While the present invention concentrates on various physical connections, other techniques may be applied alone or in combination with any of the physical connections to create a rapid expansion of the number of possible feeds.

The CTHA may have multiple sections, each with a potentially different feed, as in the four sections of the Quad-Contra configuration disclosed in Patent 5,442,369. For simplicity of disclosure, the following disclosure is with regard to a single contrawound toroidal section, although a plurality of sections may be employed to increase the possible feed configurations.

A single section CTHA has four wire ends, each of which may be: (1) left alone; (2) electrically connected to another wire end; and/or (3) electrically connected to one of two transmitter and/or receiver feed lines. Conversely, each of those two feed lines from the transmitter and/or receiver may be: (1) electrically connected to a wire end; (2) electrically connected to a group of wire ends; (3) electrically connected to something completely different (e. g., a ground plane, reflector, inductively coupled loop); or (4) left unconnected.

Figures 4A-4B show wire ends A, B, C, D for two different CTHA antennas 16,17. The CTHA antenna 16 of Figure 4A has"polar"crossings at the top and the bottom (only the crossings at the top of the antenna 16 are shown) thereof, while the CTHA antenna 17 of Figure 4B, which is shown in profile, has equatorial crossings at the outside and the inside (only the crossing at the outside of the antenna 17 are shown) thereof. In either case, two conductors 18,20 are employed with both ends in the feed area 22. The conductor 18 has ends A, D, while the conductor 20 has ends B, C.

In one embodiment of the invention, the conductors 18,20 are insulated conductors. The first insulated conductor, such as 18, extends around and over a multiply connected surface, such as the exemplary toroidal surface 23, with a first pitch or winding sense (e. g., a right-handed winding sense) from the node A to the node D. The second insulated conductor, such as 20, extends around and over the exemplary surface 23, with a second pitch or winding sense (e. g., a left-handed

winding sense) from the node B to the node C. The first and second pitch or winding senses are opposite, in order that the conductors 18,20 are contrawound relative to each other around and over the surface 23.

As disclosed, for example, in Patent 6,028,558, and as shown in Figure 5F, ends or nodes A and C are suitably electrically connected together with one electrical connection 24, and ends or nodes B and D are suitably electrically connected together with another electrical connection 26. This configuration imparts contra-currents on the two contrawound helices formed by the conductors 18,20.

Those currents, in turn, add together to form a pseudo-poloidal current, thereby reinforcing the loop magnetic flux. This arrangement is advantageous for producing vertically polarized energy from a predominately horizontal structure. In turn, those electrical connections 24,26 form respective"signal terminals", which are structured for transmitting or receiving an antenna signal 28. Another prior CTHA feed arrangement is shown in Figure 5E, in which the nodes D and C are electrically connected, and the nodes A and B are electrically connected to signal terminals for transmitting or receiving an antenna signal.

While"terminals"are not an essential part of CTHA antennas, terminals are employed herein as a mechanism for logically describing connections.

In this regard, four terminals are employed: terminals #1 and #2 represent two feed lines, and terminals #3 and #4 represent a mechanism for connecting multiple wire ends, which are not fed. In defining the various feed arrangements which are disclosed herein, each of the four wire ends A, B, C, D can, therefore, have five possible values: the value"0"means no connection, while the values"1,""2,""3," and"4"indicate a terminal connection.

The following six rules (R1-R6) are employed in defining connections herein: (Rl) if terminal #3 or #4 has a wire electrically connected to it, then it either has more than one wire electrically connected to it, or it is redundant to a configuration having no connection ; (R2) terminals #3 and #4 are interchangeable (i. e., there is no logical difference); (R3) terminals #1 and #2 are interchangeable (i. e., there is no logical difference); (R4) wire ends A and B may be swapped for ends C

and D, respectively (i. e., there is A<->C and B<->D symmetry); (R5) wire ends A and D may be swapped for ends B and C, respectively (i. e., there is A<->B and C<->D symmetry); and (R6) wire ends A and B may be swapped for D and C, respectively (i. e., there is A<->D and B<->C symmetry). Rule 6 is the same as performing rule 4 followed by rule 5. These rules are employed to remove redundant and symmetrical configurations. While this procedure is not the only method for determining all possible configurations, it is sufficiently rigorous to ensure that all configurations are identified. Also, combinations of these symmetry rules are employed to remove all redundant configurations.

Table 1 shows the effect of removing redundant feed configurations by applying successive symmetry rules. There are, thus, 35 physical ways to connect a pair of feed lines to the four wire ends A, B, C, D. In turn, these may be diversified by employing multiple segment CTHAs, or by employing, for example, inductive loops, reflectors, or ground planes, in combination with the various feed configurations.

TABLE 1 Operation Combinations 4 wire ends with 5 possible values 625 Rule (Rl) 221 Rule 2, Rule 3, and Rule 2 then Rule 3 83 (R2, R3, R2-R3) R4, R4-R2, R4-R3, R4-R2-R3 51 R5, R5-R2, R5-R3, R5-R2-R3 46 R6, R6-R2, R6-R3, R6-R2-R3 35 Table 2 defines wire end terminal connections for various CTHA feeds and divides the 35 exemplary feed configurations of Table 1 into three main groups: (1) two connection feeds; (2) one connection feeds; and (3) no physical connection feeds. The third category employs alternative feed techniques (e. g., inductive loops, reflectors, ground planes, multiple antennas, antenna coupling of passive elements in an array).

TABLE 2 Two Connections Feed # Wire A B C D 1 3 2 3 1 2 1 0 0 3 0 1 0 2 4 2 1 0 0 5 1 2 3 3 6 2 1 2 1 7 2 2 8 2 3 3 1 9 1 2 2 10 2 2 0 1 11 2 1 0 1 12 1 2 0 2 13 2 1 1 1 One Connection Feed # Wire A B C D 14 1 0 0 0 15 1 1 0 0 16 1 0 1 0 17 0 1 1 0 18 1 1 1 0 19 3 3 1 0 20 3 1 3 0 21 1 3 3 0 22 1 1 1 1 23 3 3 1 1 24 3 1 3 1 25 1 3 3 1 26 3 3 3 1 No Connections Feed# Wire A B C D 27 0 0 0 0 28 3 3 0 0 29 3 0 3 0 30 0 3 3 0 31 3 3 3 0 32 3 3 3 3 33 4 4 3 3 34 4 3 4 3 35 3 4 4 3

Figures 5A-5D and 5G-5M show various CTHA feeds, which employ two feed lines, in accordance with embodiments of the present invention. Those CTHA feeds are applicable with, for example, the exemplary antennas 16,17 of Figures 4A-4B. In the CTHA feed 30 of Figure 5A, the node A is electrically connected to the node C by electrical connection 32, although the node A of the conductor 18 may be directly electrically connected to the node C of the conductor 20. The nodes D and B in this feed are electrically connected to signal terminals 34 and 36, respectively, which are suitably structured for transmitting or receiving an antenna signal 38.

As shown in Figure 5H, in the CTHA feed 40, the node B is electrically connected to the node C by electrical connection 42. As employed herein, electrical connections, such as 32 or 42, include separate conductors, such as insulated conductors, as well as direct electrical connections of nodes, such as B and C. The nodes A and D in this feed are electrically connected to signal terminals 44 and 46, respectively, which are structured for transmitting or receiving an antenna signal 48.

For ease of reference, below, it will be understood that signal terminals are structured for transmitting or receiving a corresponding antenna signal.

Referring to Figure 5M, in the CTHA feed 50, the node B is electrically connected to the node D and to the node C by electrical connection 52.

The nodes D and A in this feed are electrically connected to signal terminals 54 and 56, respectively, for transmitting or receiving an antenna signal 58.

In the CTHA feed 60 of Figure 5G, the node A is electrically connected to the node B by electrical connection 61, and the node D is electrically connected to the node C by electrical connection 62. The nodes A, B and the electrical connection 61 are electrically connected to signal terminal 64, and the nodes D, C and the electrical connection 62 are electrically connected to signal terminal 66, for transmitting or receiving an antenna signal 68.

Referring to Figure 51, in the CTHA feed 70, the node A is electrically connected to the node D by electrical connection 71, and the node B is electrically connected to the node C by electrical connection 72. The nodes A, D and the

electrical connection 71 are electrically connected to signal terminal 74, and the nodes B, C and the electrical connection 72 are electrically connected to signal terminal 76, for transmitting or receiving an antenna signal 78.

Figures 5B-5D, 5J-5L and 6A-6H show feeds for electromagnetic antennas, such as, for example, the exemplary antennas 16, 17 of Figures 4A-4B, in which one, two or three of the nodes A, B, C, D are open.

In the CTHA feed 80 of Figure 5B, the nodes A and D are electrically connected to signal terminals 84 and 86, respectively, for transmitting or receiving an antenna signal 88, and the nodes B and C are open.

In the CTHA feed 90 of Figure 5C, the nodes D and B are electrically connected to signal terminals 94 and 96, respectively, for transmitting or receiving an antenna signal 98, and the nodes A and C are open.

In the CTHA feed 100 of Figure 5D, the nodes A and B are electrically connected to signal terminals 104 and 106, respectively, for transmitting or receiving an antenna signal 108, and the nodes D and C are open.

In the CTHA feed 110 of Figure 5J, the node A is electrically connected to the node B by electrical connection 112, the nodes A, B and D are electrically connected to signal terminals 114 and 116, respectively, for transmitting or receiving an antenna signal 118, and the node C is open.

In the CTHA feed 120 of Figure 5K, the node D is electrically connected to the node B by electrical connection 122, the nodes D, B and A are electrically connected to signal terminals 124 and 126, respectively, for transmitting or receiving an antenna signal 128, and the node C is open.

In the CTHA feed 130 of Figure 5L, the node A is electrically connected to the node D by electrical connection 132, the nodes A, D and B are electrically connected to signal terminals 134 and 136, respectively, for transmitting or receiving an antenna signal 138, and the node C is open.

In addition to showing feeds for electromagnetic antennas, such as, for example, the exemplary antennas 16,17 of Figures 4A-4B, in which one, two or three of the nodes A, B, C, D are open (Figures 6A-6H), Figures 6A-6M show CTHA feeds,

which employ only one direct feed connection in accordance with other embodiments of the present invention.

In the CTHA feed 140 of Figure 6A, the nodes D, B, C are open, a signal terminal 144 is electrically connected to the node A, and a signal terminal 146 is structured for connection to a cooperative antenna structure such as, for example, the ground plane 147 of Figure 41, the reflector 148 of Figure 42, the other CTHA 149 of Figure 43, or any other antenna structure. For convenience of reference, it will be understood that signal terminals, such as 144,146, are for transmitting or receiving an antenna signal, such as 148.

In the CTHA feed 150 of Figure 6B, the node A is electrically connected to the node B by an electrical connection 152, the nodes D and C are open, a first signal terminal 154 is electrically connected to the nodes A, B, and a second signal terminal 156 is structured for connection to a cooperative antenna structure.

The terminals 154,156 are for an antenna signal 158.

In the CTHA feed 160 of Figure 6C, the node A is electrically connected to the node C by an electrical connection 162, the nodes D and B are open, a first signal terminal 164 is electrically connected to the nodes A, C, and a second signal terminal 166 is structured for connection to a cooperative antenna structure.

The terminals 164,166 are for an antenna signal 168.

In the CTHA feed 170 of Figure 6D, the node B is electrically connected to the node C by an electrical connection 172, the nodes A and D are open, a first signal terminal 174 is electrically connected to the nodes B, C, and a second signal terminal 176 is structured for connection to a cooperative antenna structure.

The terminals 174,176 are for an antenna signal 178.

In the CTHA feed 180 of Figure 6E, the node A is electrically connected to the nodes B and C by an electrical connection 182, the node D is open, a first signal terminal 184 is electrically connected to the nodes A, B, C, and a second signal terminal 186 is structured for connection to a cooperative antenna structure.

The terminals 184,186 are for an antenna signal 188.

In the CTHA feed 190 of Figure 6F, the node A is electrically connected to the node B by an electrical connection 192, the node D is open, a first signal terminal 194 is electrically connected to the node C, and a second signal terminal 196 is structured for connection to a cooperative antenna structure. The terminals 194,196 are for an antenna signal 198.

In the CTHA feed 200 of Figure 6G, the node A is electrically connected to the node C by an electrical connection 202, the node D is open, a first signal terminal 204 is electrically connected to the node B, and a second signal terminal 206 is structured for connection to a cooperative antenna structure. The terminals 204,206 are for an antenna signal 208.

In the CTHA feed 210 of Figure 6H, the node B is electrically connected to the node C by an electrical connection 212, the node D is open, a first signal terminal 214 is electrically connected to the node A, and a second signal terminal 216 is structured for connection to a cooperative antenna structure. The terminals 214,216 are for an antenna signal 218.

In the CTHA feed 220 of Figure 6I, the node A is electrically connected to the node D by an electrical connection 221, the node B is electrically connected to the node C by an electrical connection 222, a first signal terminal 224 is electrically connected to the nodes A, B, C, D, and a second signal terminal 226 is structured for connection to a cooperative antenna structure. The terminals 224,226 are for an antenna signal 228.

In the CTHA feed 230 of Figure 6J, the node A is electrically connected to the node B by an electrical connection 231, the node D is electrically connected to the node C by an electrical connection 232, a first signal terminal 234 is electrically connected to the nodes D, C, and a second signal terminal 236 is structured for connection to a cooperative antenna structure. The terminals 234,236 are for an antenna signal 238.

In the CTHA feed 240 of Figure 6K, the node A is electrically connected to the node C by an electrical connection 241, the node D is electrically connected to the node B by an electrical connection 242, a first signal terminal 244 is

electrically connected to the nodes D, B, and a second signal terminal 246 is structured for connection to a cooperative antenna structure. The terminals 244,246 are for an antenna signal 248.

In the CTHA feed 250 of Figure 6L, the node A is electrically connected to the node D by an electrical connection 251, the node B is electrically connected to the node C by an electrical connection 252, a first signal terminal 254 is electrically connected to the nodes A, D, and a second signal terminal 256 is structured for connection to a cooperative antenna structure. The terminals 254,256 are for an antenna signal 258.

In the CTHA feed of Figure 6M, the node A is electrically connected to the nodes B, C by electrical connection 262, signal terminal 264 is electrically connected to the node D, and signal terminal 266 is structured for connection to a cooperative antenna structure. The terminals 264,266 are for an antenna signal 268.

Figures 7A-7I show various CTHA feeds, which employ no direct feed connection. In particular, Figure 7A shows CTHA feed 270 in which signal terminals 274,276 are structured for transmitting or receiving an antenna signal 278. A suitable circuit 279 couples the antenna signal 278 to or from conductors, such as the exemplary insulated conductors 18,20 of Figures 4A-4B.

In Figures 7A-7E, one, two or all four of the nodes A, B, C, D of the CTHA feeds 270,280,290,300,310 are open. Like the feed 270 of Figure 7A, it is understood that the CTHA feeds 270,280,290,300,310,320,330,340,350 of Figures 7B-7I, respectively, each employ a suitable coupling circuit, such as 279 of Figure 7A.

All of the nodes A, B, C, D of the feed 270 of Figure 7A are open. In the feed 280 of Figure 7B, the node A is electrically connected to the node B by electrical connection 282, and the nodes D, C are open. In the feed 290 of Figure 7C, the node A is electrically connected to the node C by electrical connection 292, and the nodes D, B are open. Figure 7D shows the feed 300, in which node B is electrically connected to the node C by electrical connection 302, and the nodes A, D are open. In

the feed 310 of Figure 7E, the node A is electrically connected to the node B and the node C by electrical connection 302, and the node D is open.

In Figures 7F-7I, the nodes A, B, C, D of these CTHA feeds are interconnected with at least one other node. In the feed 320 of Figure 7F, the node A is electrically connected to the node D by electrical connection 321, and the node B is electrically connected to the node C by electrical connection 322. In turn, the nodes A, D are electrically connected (e. g., at 323) to the nodes B, C. In the feed 330 of Figure 7G, the node A is electrically connected to the node B by electrical connection 331, and the node D is electrically connected to the node C by electrical connection 332. In the feed 340 of Figure 7H, the node A is electrically connected to the node C by electrical connection 341, and the node D is electrically connected to the node B by electrical connection 342.

In the embodiment of Figure 7G, the exemplary electrical connections 331,332, and the exemplary insulated conductors 18,20, include a single insulated conductor which forms a single endless conductive path around and over the surface, such as the exemplary toroidal surface 23 of Figure 4A.

In the feed 350 of Figure 7I, the node A is electrically connected to the node D by electrical connection 351, and the node B is electrically connected to the node C by electrical connection 352.

Examples 1-8 The following examples illustrate the behavior of CTHAs having feeds #1-#8 (i. e., Figures 5A-5H, respectively), as set forth in Table 2. These feeds are modeled in NEC 4 (i. e., Numerical Electromagnetics Code, Version 4, maintained by Los Alamos National Laboratory). In these examples, an exemplary 10-turn CTHA has a major radius of 1.05 in (0.413 cm), a minor radius of 0.185 in. (0.0728 cm), and a wire diameter of 0.0143 in. (0.00570 cm), and the exemplary antennas employ "polar crossings" (i. e., wire crossings above and below) as shown in Figure 4A, although a wide range of antenna geometries, sizes, and wire sizes may be employed.

The conventional CTHA feed of Figure 5F is employed as the basis of comparison for much of the following discussion. Figures 8-15 are plots of the

impedance spectrums for the CTHA feeds of Figures 5A-5H, respectively. Figure 8 shows the impedance spectrum for feed 30 of Figure 5A, which has a reduction in the frequency of the first resonance due to the effective doubling of the wire length between the two feed points 34,36. This is accomplished by electrically connecting the nodes A, C, but feeding the other two nodes D, B. The exemplary feed 30 configuration has a resonance at 300 MHz, as opposed to an anti-resonance, thereby improving impedance matching bandwidth, since the change of impedance with respect to frequency is less rapid at a resonance, as opposed to an anti-resonance.

Figure 8 and Figure 13 are based upon the same physical antenna, except that different feeds are employed. The feed 30 configuration greatly reduces the input impedance at 300 MHz, thereby improving impedance matching characteristics.

Furthermore, as discussed below, the gain and shape of the corresponding radiation pattern is typically affected by the feed configuration to, thereby, meet various communication needs.

Figure 9 shows the impedance spectrum for feed 80 of Figure 5B, which leaves the first resonance essentially the same with respect to the feed of Figure 5F, but significantly affects the regular intervals of subsequent resonances. It is believed that this is of importance when operating the exemplary antenna at higher resonances. Feed 80 is essentially a single toroidal helix, as formed by the exemplary conductor 18, which has a second contrawound toroidal helix, as formed by the exemplary conductor 20, passively coupled thereto. It is believed that the irregularity in the impedance spectrum of Figure 9 coincides with varying degrees of coupling between the CTHA wires.

The impedance spectrum of feed 90 in Figure 10 is relatively chaotic from the perspective of regular interval resonances, although it is believed that it has a useful design point at its third resonance 99.

Figure 11 shows an impedance spectrum for feed 100 of Figure 5D, which switches to a low impedance first resonance 101. This is possible by leaving the nodes D, C of Figure 5D unconnected. This spectrum essentially changes a low current feed (e. g., such as a loop) to a high current feed (e. g., such as a dipole), and

exhibits regularly spaced resonances at 150 MHz intervals. It is believed that this impedance spectrum may be advantageous at 300 MHz. Furthermore, it is believed that it has similar currents with respect to the feed of Figure 5F and, therefore, should advantageously produce vertically polarized energy from an exemplary horizontal toroid.

Figure 12 shows the impedance spectrum of the feed of Figure 5E, which has regular interval resonances beginning at 150 MHz due to the effective increase in wire length between the two feed points at nodes A, B.

Although the feed of Figure 5F (the corresponding impedance spectrum is shown in Figure 13) imposes contra-currents in the contrawindings 18,20 and, hence, augments magnetic fields at the expense of azimuthal phi-polarized electric fields, the feed 60 of Figure 5G imposes similar currents in the contrawindings, thereby maximizing azimuthal phi-polarized electric fields at the expense of magnetic fields. It is believed that this feed is advantageous for horizontally polarized communication and is especially beneficial at vertically polarized radiation in the vertical position (i. e., when employed in a"lollipop mode").

Of particular interest is the relatively large change in the first resonance, as shown by the corresponding impedance spectrum of Figure 14, which is due to a greatly changed effective velocity factor when employing similar currents.

The feed 40 of Figure 5H is similar to the feed 80 of Figure 5B in that there is one driven helix and one passively coupled helix. However, by closing the second helix (i. e., between the nodes B, C), the coupling now follows a more uniform behavior as shown in the impedance spectrum of Figure 15.

The exemplary feeds 30 (Figures 5A and 8), 80 (Figures 5C and 10), and 100 (Figures 5D and 11) lead to a lowering of the first resonance frequency relative to the feed of Figures 5F and 13, while feeds 60 (Figures 5G and 14) and 40 (Figures 5H and 15) increase the first resonance frequency, and feed 80 (Figures 5B and 9) maintains that first resonance frequency.

Figure 16 shows a plot of calculated resonant frequencies between 5 and 1000 MHz for a CTHA having the feeds of Figures 5A-5H. The impedance

spectrum for the feed #6 of Figure 5F has regular interval resonances starting near 300 MHz and alternates between high impedance and low impedance throughout the spectrum. The first resonance refers to the first crossing of the x-axis by the reactance portion of the impedance, even if that crossing represents a discontinuity or anti- resonance. In this plot, the feeds of Figures 5D-5F maintain evenly spaced resonance intervals, while the feeds of Figures 5A-5C, 5G and 5H vary to some extent.

Table 3, below, shows the computed resonant frequencies (MHz) for the feeds of Figures 5A-5H.

TABLE 3 Feed Feed Feed Feed Feed Feed Feed Feed Resonance #1 #2 #3 #4 #5 #6 #7 #8 1 156. 67 302. 59 157. 14 148. 82 141. 51 302.51 542.40 360.80 2 304. 96 361. 45 548. 16 302. 49 305. 23 597.26 598.95 3 587. 89 547. 66 595. 75 457. 02 456. 70 917.73 828.84 4 926. 01 843. 38 601. 23 602. 86 599. 60 5 916. 42 756. 71 753. 26 6 916. 67 924. 84 Figure 17 is a plot of the real part of the impedance at various resonances between 5 and 1000 MHz for the feeds of Figures 5A-5H, respectively.

The feeds of Figures 5A, 5B, and 5E-5H start at relatively high impedance resonances (i. e., the first resonance looking left to right-the first crossing of the reactance across the frequency axis is referred to as a resonance) (see Figures 8,9 and 12-15, respectively). In this regard, if the resistance curve has a relatively high value at the place the reactance crosses the frequency axis, then this is referred to as a high impedance resonance. Otherwise, if, at the resonance, the resistance curve has a relatively low value, then this is referred to as a low impedance resonance.

Alternatively, some might call the high impedance resonance an"anti-resonance".

Each impedance spectrum generally shows a repeating pattern of high and low impedance resonances. Some start low and then proceed to high, low, high, etc.; while others start high and then proceed to low, high, low, etc. Some of the feed

arrangements disclosed herein are such that the magnetic fields are cancelled and the electric fields are reinforced for applications where a loop antenna pattern is desired, but is smaller in size due to its helical nature.

Figure 18 is a plot of maximum azimuthal gains for the feeds of Figures 5A-5H, respectively, at the respective first resonances. An important design consideration is the gain of an antenna. This plot provides an interesting comparison for a fixed size antenna. However, in most applications, the frequency is fixed and a different sized antenna would be employed for each feed in order to provide the same first resonance. Hence, better comparison of the feeds may be obtained. From a pure gain perspective, the feed (#7) of Figure 5G is preferred to the extent that energy being completely phi polarized (max_Az_phi) is desired. In that regard, such a polarization may solve various communications problems (e. g., the CTHA acts like a loop antenna, but is smaller than a traditional loop), although it deviates from the traditional CTHA concept of a horizontal structure, which produces vertically polarized radiation.

Figure 19 is a plot of average azimuthal gains for the feeds of Figures 5A-5H, respectively, at the respective first resonances.

Figure 20 is a plot of average azimuthal gains for the feeds of Figures 5A-5H, respectively, at the respective first resonances as shown at the frequency of those resonances. This plot shows that the variation in average gain (0, , and total) at the respective first resonances is due to changes in frequency of these resonances.

In general, if frequency were the only factor, then all of the points would fall on the same curve. Since this is not the case, then it is believed that there are relative efficiency differences for the respective feed configurations of Figures 5A-5H.

Figures 21A-21C through 28A-28C are far-field plots of theta- polarized gain (Figures 21A-28A), phi-polarized gain (Figures 21B-28B), and total gain (Figures 21C-28C) for the feeds of Figures 5A-5H, respectively, at the respective first resonances. These plots show the relative shapes and magnitudes of the radiation patterns for those feeds. The null 360 (Figure 21B) and the null 362 (Figure 23B) are relatively deep nulls in the phi-polarized gain pattern where very large drops in

performance are observed, such as, for example, above and below in the case of a vertical dipole (not shown). These nulls are in contrast to simple dimples or flat spots (see Figure 26B) typically observed with the feed of Figure 5F. The nulls, for example, may be employed to reject noise from unwanted sources. Benefits in the input impedance spectrum as derived, for example, from non-symmetric feeds, such as the feed 80 of Figure 5B, yield non-symmetry in the corresponding radiation pattern as shown in Figures 22A-22C.

Figures 29-31 show various slices of the 3D radiation patterns of Figures 21A-28C, in order to better illustrate relative quantities. These comparisons are at the respective first resonances and, therefore, are not at the same frequency.

Figure 29 shows an azimuth cut of theta-polarized gain versus phi-degrees at each of the first resonances for the respective feeds of Figures 5A-5H. Figures 30 and 31 similarly show an azimuth cut of phi-polarized gain versus phi-degrees, and an azimuth cut of total gain versus phi-degrees, respectively.

Figures 32-34 illustrate the relative performance of a CTHA antenna, which employs the different feeds of Figures 5A-5H, throughout the spectrum. Figure 32 is a plot of total gain versus frequency averaged over the entire far-field sphere in order to approximate efficiency. Figures 33 and 34 are plots of theta-polarized gain and phi-polarized gain, respectively, versus frequency averaged over the azimuth cut.

Figure 32 shows that the feed of Figure 5F is not the most efficient radiator; however, comparison between Figure 32 and Figure 34 shows that the most efficient feeds are those that excel in the production of phi-polarized energy in the azimuthal plane. It is believed that these relatively efficient antenna feeds will solve various communication needs. For example, feed 60 (Figure 5G) has high efficiency, as shown in Figure 32, but low theta-polarized energy in the azimuthal plane, as shown in Figure 33, and high phi-polarized energy in the azimuthal plane, as shown in Figure 34, which would make it preferred for television, as contrasted with FM radio.

An original goal of obtaining vertically polarized energy from a low profile antenna is best judged from Figure 33 for the azimuthal plane. From 450 MHz and up (about 1.5 times the first resonance of the feed of Figure 5F), the feed of

Figure 5F has a relatively high efficiency, as do feed 100 of Figure 5D and the feed of Figure 5E. While not more efficient, it is believed that these latter two feeds may be more readily matched at 450 MHz, due to proximity of the resonances.

Furthermore, the feed 40 of Figure 5H appears to have one highly efficient point at its second resonance of 600 MHz. Also, below 450 MHz, feed 30 (Figure 5A) and the feed of Figure 5E are more efficient than the feed of Figure 5F.

Further, below 300 MHz, the feeds 90 (Figure 5C) and 100 (Figure 5D) are also more efficient than the feed of Figure 5F at theta-polarized radiation in the azimuth plane.

While that latter feed usually produces one of the more spherical theta-polarized patterns, the strong phi-polarized feeds 30,90,60,40 (Figures 5A, 5C, 5G, 5H, respectively) are more spherical in the phi-polarized radiation. The diverse resonances have an effect on where various feeds are more spherical throughout the spectrum.

The exemplary relationships disclosed herein are for a single fixed- geometry antenna having different feeds. A different set of relationships may result from scaling the antennas with different feeds in order that they all have the same first resonance.

Operation of CTHA antennas, which employ the feeds disclosed herein, either on or off of resonance is a matter of providing a suitable matching mechanism in order that energy is successfully coupled into the antenna and standing waves are established to successfully radiate (or receive) the energy. Since this can be achieved almost anywhere in the impedance spectrum, the different feeds may be compared for efficiency without regard to their natural resonances.

As employed herein, the term sphericity quantifies the isotropic nature of the radiation pattern (i. e., smoothness over the sphere, not efficiency). The quantity developed here is roughly analogous to the standard deviation or variance of the gain over the entire sphere. As such, smaller numbers correspond to more spherical, or more isotropic, patterns.

Figure 35 is a plot of sphericity theta-polarized gain versus frequency for the respective feeds of Figures 5A-5H over the entire far-field sphere. Similarly,

Figures 36 and 37 are plots of sphericity phi-polarized gain and sphericity total gain, respectively, versus frequency for those feeds over the entire far-field sphere.

Figures 38A-38C show far-field patterns for a conventional vertical loop produced for a full k resonance. The field patterns are similar to those of a CTHA employing the feed of Figure 5F (see Figures 26A-26C) at second resonance (i. e., the full k resonance). Figures 39A-39C show far-field patterns for a conventional horizontal loop. Figures 38A and 39A show theta-polarized gain, Figures 38B and 39B show phi-polarized gain, and Figures 38C and 39C show total gain. These patterns illustrate similarities between full size vertical and horizontal loops and compact CTHAs.

Figures 40A-40B show simulated currents versus length along the conductors in the two helical contrawound windings for the feeds of Figures 5A-5H.

These show that the feeds of Figures 5E and 5F produce contra-currents, while the feed 60 of Figure 5G produces similar currents, or co-currents. The relative magnitudes of the currents of the respective feeds vary as well. The second loop of feed 40 of Figure 5H resonates naturally with a contra-current, but is not centered on the vertical current axis. Since the second loop of feed 40 is not electrically connected to that feed, it is free to float at some DC value above the driven helix center.

Figure 41 shows an electromagnetic antenna 370, which employs ground plane 147, in order to form a monopole antenna. In this example, the signal terminal 246 of the feed 240 is electrically connected to the ground plane 147.

Figure 42 shows an electromagnetic antenna 380, which employs reflector 148. In this example, the signal terminal 246 of the feed 240 is electrically connected to the reflector 246.

Figure 43 shows an electromagnetic antenna 390, which employs a second CTHA antenna 149. In this example, the signal terminal 246 of the feed 240 is electrically connected to the second antenna 149.

Although reference is made in Figures 41-43 to the exemplary feed 240 of Figure 6K, these examples are applicable to any of the exemplary feeds of Figures 6A-6M.

Figure 44 shows an electromagnetic antenna 400 in which the antenna signal 402 is capacitively coupled to contrawound insulated conductors 404,406. A suitable circuit 408 is employed to capacitively couple the antenna signal 402.

Figure 45 shows an electromagnetic antenna 410 in which signal terminals 412,414 provide antenna coupling of a passive CTHA element 416 in an array with an active dipole 418.

Figure 46 shows an electromagnetic antenna 420 in which signal terminals 422,424 provide antenna coupling of passive CTHA elements 426,427 in an array with an active CTHA 428.

Figure 47 shows an example of a conventional shielded loop 430 which is employed to magnetically couple an RF signal at signal carrying terminals 431,432 to or from a CTHA antenna 433. The shielded loop 430 is formed by a coaxial cable 434 (e. g., 50 Q), in which the shield 435 is cut at 436 and 438 to expose the center conductor 440. In turn, the center conductor 440 and the corresponding shield 435 are electrically connected to the exposed shield 435 at 441. The exposed center conductor 440 (or cut shield) at 436 serves to stop the current flow in the shield 43 5. Although no electrical connection is made from the coupling loop 442 to the antenna 433, the loop 442 is suitably positioned in proximity to the CTHA 433, and preferably without passing completely around the exemplary toroidal surface, in order to couple and match RF energy to or from the antenna 433. Preferably, the size of the loop 442 is relatively small with respect to the wavelength, A, of the RF signal at terminals 431, 432.

Figures 48 and 49 show other variations of multiply connected surfaces 450 and 452, respectively. The surface 450 has a cross-section 454, which is a generally connected form. The surface 452 is a generalized toroid having a cross- section 456, which is non-circular (e. g., oval, elliptical, egg-shaped).

As disclosed in Patent 6,028,558, the exemplary contrawound conductors or conductive paths, such as the exemplary insulated conductors 18,20 of Figure 4A, may be contrawound helical conductive paths having the same number of turns, with the helical pitch sense for one conductive path being right hand (RH), and the helical pitch sense for the other conductive path being left hand (LH), which is opposite from the RH pitch sense. The exemplary conductive paths disclosed herein may be arranged in other than a helical fashion, such as a generally helical fashion, a spiral fashion, a caduceus fashion, or any contrawound fashion, and still satisfy the spirit of this invention. The conductive paths may further be contrawound"poloidal- peripheral winding patterns"having opposite winding senses (e. g., the helix formed by each of two insulated conductors is decomposed into a series of interconnected poloidal loops) (see, for example, Patent 5,442,369). Although exemplary insulated conductor windings 18,20 are disclosed herein, such conductors need not be entirely insulated. In other words, such conductors, while being isolated from each other (except at points where electrical connections are intended), may employ other forms of insulation (e. g., without limitation, air gaps).

As disclosed herein, different modes of operation of the CTHA may be induced by different feed configurations.

While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.