Communications: radio wave antennas – Antennas – High frequency type loops
Reexamination Certificate
1999-04-05
2001-11-20
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
High frequency type loops
C343S744000, C343S866000, C343S895000
Reexamination Certificate
active
06320550
ABSTRACT:
TECHNICAL ART
The instant invention generally relates to antennas for transmitting and receiving electromagnetic radiation, and more particularly to contrawound helical antennas.
BACKGROUND OF THE INVENTION
Application Ser. No. 08/514,609, the '609 Application, teaches an electrically small contrawound toroidal helical antenna (CTHA) comprising a single conductor with two length portions in overlapping contrawound relationship to one another. Electrical currents in the individual length portions travel in opposite circumferential directions around the toroid, so that the net circumferential electric current around the toroid is effectively zero. However, because of the contrawound helical relationship, the associated circumferential magnetic current components created by the respective electric current components in each of the toroidal helical length portions reinforce, so that the resulting radiation pattern is similar to that of an electric dipole coincident with and centered along the major axis of the torus. In other words, the resulting radiation pattern is strongly linearly polarized in a direction parallel to the major axis of the toroid. Depending upon the construction of the antenna, particularly the aspect ratio of the underlying torus form and the number of helical turns, other polarization components may also be present.
The '609 Application, incorporated by reference herein, teaches a schematic symbolism for representing generalized helical and generalized toroidal helical windings as solid or dashed lines, the former representing a left had pitch sense, the later representing a right hand pitch sense, wherein the axial direction of the associated magnetic current and the projected axial direction of the associated electric current are the same for a right hand pitch sense helix, and opposite for a left-hand pitch sense helix. The radiation pattern of an electromagnetic antenna can be related to the effective electric and magnetic current distributions created by the antenna. For example, a uniform ring of magnetic current with no associated electric currents corresponds to the radiated electromagnetic field distribution of an electric dipole antenna. Furthermore, a uniform ring of electric current with no associated magnetic currents approximates the radiation pattern of a “Smith Cloverleaf” antenna. The radiation pattern for a particular set of current distributions can be determined by either simulation or measurement.
In an exemplary mode of operation, the antenna is operated at a frequency such that the circumferential length of the antenna is one half of an electrical wavelength. The slow wave properties of the contrawound helix make the corresponding physical length shorter than the free space wavelength according to the associated velocity factor, which depends upon the associated underlying helix geometry.
One limitation of the above described contrawound toroidal helical antenna is that the bandwidth of the antenna is about 10%. Accordingly, for broadband applications for which a greater bandwidth is required, a plurality of contrawound toroidal helical antennas are necessary wherein the respective resonant frequencies of the antennas are separated from one another in such a manner that for a given frequency of operation within the associated frequency band, the one of the plurality of antennas having the lowest VSWR at the transmission line side of the associated impedance matching network is used for transmitting or receiving the given signal. Accordingly, as illustrated in
FIG. 76
of the '609 Application, a broadband signal may be directed to or extracted from the appropriate antenna using a multiplexer. In another embodiment, individual transceivers could be adapted to each antenna element. In yet another embodiment, a multiplexer may be used to interface one transmitter with a plurality of antenna elements, and individual receivers may be operatively coupled to each of the antenna elements, the outputs from which are combined so as to form a composite received signal.
As illustrated in the above referenced
FIG. 76
, the individual antenna elements are concentrically co-located about a common central axis. This has the advantage of providing for phase symmetry of the resulting transmitted waves with respect to the common axis. However, one problem with this arrangement is that transmission line sides of the respective impedance matching networks cannot be interconnected to a common signal port without incorporating transmission line segments between one or more of the impedance matching networks and the common signal port because of the physical separation between the antenna elements. These transmission line segments introduce phase delays in the signal that are a function of frequency, which precludes the direct interconnection of the transmission line sides of the respective impedance matching networks so as to achieve natural broadband operation a the common signal port.
Another limitation of the above described contrawound toroidal helical antenna is that the antenna input impedance is generally significantly different from the characteristic impedance of typical transmission lines, which therefore requires the use of an associated impedance matching network in the signal connector. More particularly, for a relatively wide bandwidth resonance condition, the input impedance of the antenna is generally from 1 to 3 K&OHgr;. By contrast, typical transmission lines have an impedance of 50-300&OHgr;.
SUMMARY OF THE INVENTION
The instant invention overcomes the above-noted problems by providing a magnetic dipole antenna shaped so as to produce a uniformly directed circulation of magnetic current by each of the associated magnetic dipole elements, thereby causing a radiation pattern similar to the contrawound toroidal helical antenna of the '609 Application. In one elementary embodiment, the magnetic dipole antenna is antisymmetric, for example “S” or “Z” shaped, wherein the magnetic currents on respective magnetic dipole elements are each directed in the same direction relative to the center of the magnetic dipole antenna. In another elementary embodiment, the magnetic dipole antenna is symmetric, for example circularly shaped, wherein the magnetic currents on respective magnetic dipole elements are each directed in opposite directions relative to the center of the magnetic dipole antenna. In yet another elementary embodiment, a magnetic monopole antenna comprises a single magnetic dipole element arranged so as to generate a circulation of the magnetic current.
The magnetic dipole elements comprise a variety of contrawound helical structures, either parallel/transmission line fed or series/loop fed; either electrically open or electrically closed.
A plurality of elementary magnetic dipole antenna elements may be combined in a magnetic dipole antenna system. If each of the elementary magnetic dipole antenna elements in a plurality is tuned for the same operating frequency and are characterized by a relatively high input impedance at the operating frequency, then the combination thereof provides for a lower composite input impedance that is easier to match to a transmission line. If each of the elementary magnetic dipole antenna elements in a plurality is tuned for a different operating frequency and is characterized by a relatively high input impedance at the operating frequency, then the combination thereof provides for a relatively broad bandwidth antenna that can be readily adapted to a single signal port.
Accordingly, one object of the instant invention is to provide an improved magnetic antenna that creates a circulation of magnetic current.
A further object of the instant invention is to provide a relatively small, low profile antenna that is polarized along the direction of magnetic circulation
A yet further object of the instant invention is to provide an improved contrawound helical antenna having an associated input impedance that is closer to the impedance of conventional transmission lines.
A yet further object of th
Nguyen Hoang
VanVoorhies Kurt L.
VorteKx, Inc.
Wong Don
LandOfFree
Contrawound helical antenna does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Contrawound helical antenna, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Contrawound helical antenna will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2586400