The present invention relates to a broadband antenna system, and more particularly, to a modified conical antenna structure wherein the feed region is cut away to form a substantially cylindrical shape termed herein “coneless.” The enlarged feed region and distribution of tapered feed points around the circumference of the “coneless” cylinder permit the collinear and coaxial stacking of multiple antenna elements or other devices. The additional antennas or other devices may be disposed within or stacked on the shaped antenna structure without interfering with the performance of the antenna system, thus providing a wide range of sensing, transmitting, receiving and other capabilities for the overall system. Multiple feed lines, cables, piping, tubing or other structures may be run through the hollow center of one or more coneless elements to feed, power or operate the stacked devices. By combining one or more coneless elements with other antennas, the antenna system of the present invention may provide a virtually infinite bandwidth.
Monocone and bicone (also termed biconical herein) antennas are well-known in the art. Many variations on the basic design of the monocone (cone, feed and ground plane) and bicone (pair of cones, feed and balun, with or without ground plane) are known. Applicant has developed an innovative “coneless” design that provides comparable or better performance relative to the known monocone and bicone antennas. The coneless design preserves the desirable performance of a conical antenna, but achieves advancement in antenna capability that has been desired, but not realized, for many years. The present invention is a simple, robust and inexpensive multifunctional antenna system that provides high gain over a large bandwidth. The innovative shape of the feed region of the present invention, having “tapered feed points” disposed substantially at the circumference of the cylindrical antenna structure, opens up the typical conic tip region of known monocone and bicone designs. The one or more tapered feed points replace the single feed/single conic tip that typically feeds known monocone antennas or the single feed/two conic tips of known bicone antennas. For optimal performance, the circumferential spacing of the tapered feed points is less than half a wavelength at the highest frequency of operation.
In order to improve bandwidth coverage, as well as gain, it is well-known to combine multiple antennas. Applicant has previously disclosed an ultra-broadband antenna system (U.S. Pat. No. 7,339,542, assigned to Assignee of the present invention) that combines an asymmetrical dipole (covering intermediate frequencies), fed with a biconical dipole (covering high frequencies), that together act as a monopole (covering low frequencies), all in a single tubular structure. The design of U.S. Pat. No. 7,339,542, including the use of a choke to limit interference, resulted in an ultra-broadband antenna system with a frequency span greater than 500:1. Nonetheless, this antenna system was limited by the very small opening in the conic tips of the biconical dipole, which resulted in coupling and interference. In order to combine additional elements with this ultra-broadband antenna system, Applicant has applied the coneless shape of the herein-described monocone to the biconical antenna element. The cut-away or shaped design of the feed region of the present invention opens up the typical “cone” of the prior art conical antennas, making a larger opening in the center of the antenna structure. Indeed, the diameter of the coneless element is substantially as large as that of the cylinder of the tubular antenna structure. This allows antenna feed lines or a wide variety of cables, such as coaxial, power, digital, fiber optic, wire, etc., as well as piping, tubing, actuators or other structures, to be run through the center of the antenna with minimal to no interference with the standalone antenna performance. For the biconical antenna of the present invention, the coneless elements may be aligned, or the elements may be clocked to improve performance in azimuth.
Another approach to providing wider bandwidth and improving gain has been to stack biconical radiators. Those skilled in the art have long studied the cone angle, overall length of the antenna, and diameter of the biconical elements in attempts to provide impedance matching of the antenna elements. An unsolved problem has been providing the feed to the stacked biconical structures without interfering with the RF performance of the lower biconical element. The innovative design of the present invention provides the same impedance matching and RF performance of known single feed point biconical structures, by positioning the one or more tapered feed points on the circumference of the cylindrical feed region. Stacking two coneless biconical elements results in higher gain at a given bandwidth; the present invention allows stacking of three, four or even more coneless biconical elements, for even higher gain, which provides the advantages of both increased range and reduced power requirements. To provide a wider frequency range, elements of differing diameters and/or differing length may also be stacked, without degradation in performance of the individual elements. At the same time that it provides greater bandwidth and/or higher gain, the innovation of present invention can allow reduction in the size of the antenna system, such as height, footprint, or diameter, or allow the system to be made conformal.
Thus, the innovative design of the coneless elements not only provides the physical space for feed lines to be run through the center of the tubular antenna structure, it also allows a wide range of devices to transmit and receive RF, audio, video and other optical frequencies, or other signals without interfering with the performance of the antenna system. In addition, non-electrical feeds, such as hydraulic, pneumatic and mechanical controls or actuators, and gas, liquid or solid material transfer systems, may also be run through the center of the antenna without degrading performance. The innovation of the present invention thus has many practical applications. Devices such as cameras, IR sensors, GPS devices, lights, audio equipment, radar equipment and communications equipment all may be mounted on the top of a multiple element, tubular antenna system that has a relatively small footprint. Where preferable, such devices may also be mounted in between multiple antenna elements. In many situations, this may obviate the need for multiple (separate) antennas, which otherwise would have to be placed apart in order not to interfere with each other.
By allowing the collinear and coaxial stacking of multiple antennas, the present invention is able to provide an antenna system with virtually unlimited bandwidth. Further, the present invention allows for both directional and omni-directional coverage, depending on the type of antennas combined.
Applications for the present invention, allowing for a wide variety of multiple stacked antennas and/or other devices, include placement on land vehicles, ships, planes, helicopters or spacecraft; land-based or sea-based locations; as well as man-portable uses.
The known art of antennas is voluminous. Applicant believes that the present invention may distinguished from the relevant prior art as follows. Typical known conical and biconical antennas, exemplified by the work of Carter, such as U.S. Pat. No. 2,175,252, disclose a single conical feed point that excites the cone-shaped radiator, which may be a single cone disposed above ground, or two cones about the same axis forming a bicone. The conical shape provides an impedance appearing almost as a pure resistance, or has no reactive component with variation in frequency, thus is useful over a wide frequency range. U.S. Pat. No. 2,416,698 to King discloses a single biconical with one feed point, having a hollow central cylinder. U.S. Pat. No. 2,543,130 to Robertson discloses yet another early biconical antenna, having a hollow pipe guide connected to a horn-shaped radiator for improved impedance matching. Like the present invention, monocones and bicones give broadband performance. Unlike the present invention, however, the foregoing designs do not permit the stacking of multiple antenna elements or other devices, because feed lines or cables cannot be run from the hollow central elements through the feed region without causing interference.
Another type of known antenna which does permit stacked collinear elements employs a traveling wave feed system. U.S. Pat. No. 2,471,021 to Bradley discloses a plurality of stacked biconical horn antennas, which use a driving network to couple into a circular wave guide through symmetrically arranged slots. U.S. Pat. No. 3,605,099 to Griffith discloses an antenna with stacked pairs of frustoconical reflector elements attached to a central hollow support member containing a central conductor. Feed is via traveling wave transmission through slots, connecting adjustable probes between the slots and the central conductor. U.S. Pat. No. 4,225,869 to Lohrmann discloses a multicone antenna having ¼ wavelength cones at each slot of a slotted ring antenna. U.S. Pat. No. 6,593,892 to Honda et al. discloses stacked biconical elements with a single center feed line. This class of antennas can be relatively broadband, and permit stacking of collinear biconical elements. The feed method of such systems is fundamentally different from that of the present invention, however, as the traveling wave is not an independent direct feed to each element. Further, all antennas using traveling wave feed are roughly the same type and size, whereas the present invention may combine a wide range of different antennas and different devices. Although traveling wave antenna systems potentially could accommodate additional devices in the collinear array by running cables or piping through the central conductor, energy is bled off as it proceeds through the slotted structure and therefore the feed to each element is not isolated, as is the case in the present invention. The functionality is limited because it does not have full control over phase and amplitude weighting. This approach also does not allow the ability to use antennas that perform at different frequency bands or perform independently of each other.
An alternate approach that allows stacking of antenna elements is to choke the antenna feed or route the feed externally. U.S. Pat. No. 3,727,231 to Galloway et al. discloses a collinear dipole array antenna with independent feeds using a narrowband technique which connects a coaxial cable to an external transmission line, in combination with λ/4 chokes for isolation, allowing a maximum of two elements.
U.S. Pat. No. 4,410,893 to Griffee discloses a collinear dual dipole antenna, also using a narrowband technique to jump the gap between two biconicals. U.S. Pat. No. 5,534,880 to Button et al. discloses multiple stacked bicone antennas with a bundle of transmission lines helically wound about the cylindrical periphery of the biconical antennas. This design uses exterior routing of cable to minimize the interference problems of passing the cables up the central column. U.S. Pat. No. 6,268,834 to Josypenko discloses multiple bicone antennas wherein the feed cable is led to a center point, then directed radially along the cone to an inductive short, through the inductive short, then directed along the surface of another cone to the center line. Again, this exterior routing of the cables minimizes the pattern perturbation. As exemplified by the foregoing, such designs do allow stacked elements and do have direct feeds to the antenna elements, but unlike the present invention, employ either a choked, centrally-fed system that permits only a relatively narrowband performance, or an externally-routed feed system for broader band operation.
U.S. Pat. No. 7,170,463 to Seavey discloses a broadband communications antenna system with center-fed, stacked dipole elements having conical shaped feed points and isolated with ferrite chokes (coiled inductors across the junction). The chokes are in close proximity to the actual feed, thus reducing the radiation efficiency of the antenna system. U.S. Patent Application Publication No. 2008/0143629 to Apostolos discloses a coaxial multi-band antenna combining a VHF, a UHF and a satellite antenna on a common radiating element, using meander line or ferrite chokes to isolate the feeds for each antenna. Unlike the narrowband choked designs of Galloway and Griffee, Seavey's and Apostolos' systems are relatively broadband, like that of Applicant's U.S. Pat. No. 7,339,542. The design of the present invention, however, obviates the need for chokes to isolate the feeds for stacked elements, thus is an improvement over all choked configurations and provides significantly greater efficiency and bandwidth.
In yet another approach, stacked, collinear and relatively broadband antenna systems are made possible by using waveguide structures to provide independent separate feeds to the antenna elements. U.S. Pat. No. 4,477,812 to Frisbee, Jr. et al. discloses a collinear array receiver system with a dipole antenna mounted atop the array. Using slot excitation, however, a system such as Frisbee, Jr.'s must be electrically large, on the order of tens of wavelengths, in order to allow space for transmission via slot. The present invention, in comparison, is on the order of one wavelength, and therefore provides the desired performance using a greatly reduced footprint. U.S. Pat. No. 6,864,853 to Judd et al. discloses stacked elements (a dipole combined with patch antenna elements) in a unitary structure that provides both directional and omnidirectional beam coverage, as well as a stack of bi-conical elements each having a frusto-conical reflector portion that together form a central passageway containing a feed system of coaxial cables. The omnidirectional array of bi-conical antennas configured end-to-end appears to use a waveguide feed structure, that, again, would be electrically large. Like the foregoing, the present invention utilizes independent separate feeds for each antenna element, but does not require the electrically large conical radiators of these waveguide-fed structures.
Finally, the prior art includes another antenna type that allows stacking of coaxial and collinear antennas. Termed “CoCo” antennas, these systems incorporate the feed system as part of the radiating structure. Examples are found in U.S. Pat. No. 6,947,006 to Diximus et al., which discloses a stacked collinear narrowband antenna that radiates on the transmission line structure, and in the 2006 paper “Generalized CoCo Antennas” by B. Notaro{hacek over (s)}, M. Djordjević and Z. Popović, which presents recent contributions to the theory and design of transmission-line antennas. This paper notes that the “CoCo antenna is inherently narrowband, and as such intended for practically single-frequency operation,” and therefore has a very different functionality from the present invention. As well, the feed mechanism of CoCo antennas is distinct from that of the present invention, which as described above, has the transmission line structure isolated from the radiating structure.
Additional objects and advantages of the invention are set forth, in part, in the description which follows and, in part, will be apparent to one of ordinary skill in the art from the description and/or from the practice of the invention.
In response to the foregoing challenge, Applicant has developed an innovative broadband antenna system allowing multiple antennas or other devices to be stacked collinearly, or disposed coaxially, in a single tubular structure, without interfering with the performance of the antenna system. As illustrated in the accompanying drawings and disclosed in the accompanying claims, the invention is a broadband antenna system comprising at least one modified conical radiating element having a radiating portion with a first circumference, a substantially cylindrical feed portion with a second circumference and that comprises at least one tapered feed point, and a first at least one operating structure connected to and operating the feed portion, wherein the at least one tapered feed point may be disposed substantially on the second circumference of the substantially cylindrical feed portion. The first at least one operating structure may further comprise a feed line, a coaxial cable, a transmission line, a twin lead, a stripline, and a microstrip. The at least one modified conical radiating element may be a modified monocone disposed on a ground plane or a modified bicone having a balun.
The broadband antenna system may further comprise at least one device collinear to or coaxial with the at least one modified conical radiating element; a second at least one operating structure, disposed within the at least one modified conical radiating element and connected to the at least one device; and the at least one device may be operated by the second at least one operating structure, without interfering with the performance of the at least one modified conical radiating element or other antenna elements. The second at least one operating structure may further comprise a feed line, a coaxial cable, a power cable, a digital cable, a fiber optic cable, a wire, piping, tubing, a mechanical actuator, a gas transfer system, a liquid transfer system, and a solid material transfer system.
As embodied herein, the at least one modified conical radiating element of the broadband antenna system may be a modified monocone disposed on a ground plane or a modified bicone having a balun. The at least one device may further comprise at least one modified bicone, and a plurality of the at least one modified bicone may be stacked collinearly, separated by a dielectric isolator therebetween each of the plurality of the modified bicone, and operated by a plurality of the second at least one operating structure.
The broadband antenna system of the present invention may further comprise a plurality of the at least one tapered feed point, and the distance between each of the plurality of the at least one tapered feed point around the circumference of the substantially cylindrical feed portion may be less than ½ wavelength of the highest frequency of operation.
In addition, the broadband antenna system of the present invention may further comprise at least one modified conical radiating element having a radiating portion, a feed portion comprising at least one tapered feed point, and a first at least one operating structure connected to and operating the feed portion, wherein the radiating portion is substantially cylindrical with a first circumference, the feed portion is substantially cylindrical with a second circumference coincident with the first circumference of the radiating portion, and wherein the at least one tapered feed point is disposed substantially on the second circumference of the feed portion. The first at least one operating structure may further comprises a feed line, a coaxial cable, a transmission line, a twin lead, a stripline, and a microstrip.
In this embodiment, the at least one modified conical radiating element may be a modified monocone disposed on a ground plane or a modified bicone having a balun. In additional embodiments, the balun of the bicone or bicones may be vertically disposed, horizontally disposed, or may be an integrated wraparound balun that is vertically disposed in the at least one modified bicone, and the at least one bicone may be formed by rolling a flexible microwave substrate material.
According to this embodiment, the broadband antenna system of the present invention may further comprise at least one device collinear to or coaxial with the at least one modified conical radiating element; a second at least one operating structure, disposed within the at least one modified conical radiating element and connected to the at least one device; and the at least one device may be operated by the second at least one operating structure, without interfering with the performance of the at least one modified conical radiating element or other antenna elements. The second at least one operating structure may further comprise a feed line, a coaxial cable, a transmission line, a twin lead, a stripline, and a microstrip, a power cable, a digital cable, a fiber optic cable, a wire, piping, tubing, a mechanical actuator, a gas transfer system, a liquid transfer system, and a solid material transfer system.
According to this embodiment, the at least one modified conical radiating element may be a modified monocone disposed on a ground plane or a modified bicone having a balun.
In the broadband antenna system according to this embodiment, the at least one device may further comprise at least one modified bicone, and a plurality of the at least one modified bicone may be stacked collinearly, separated by a dielectric isolator therebetween each of the plurality of the modified bicone, and operated by a plurality of the second at least one operating structure.
As disclosed herein, the at least one device may be a radiating antenna, another type of antenna element, a GPS system, a camera, an IR sensor, a light, an audio device, a radar device, and a communications system. In additional embodiments, the balun of the bicone or bicones may be vertically disposed, horizontally disposed, or may be an integrated wraparound balun that is vertically disposed in the at least one modified bicone, and the at least one bicone may be formed by rolling a flexible microwave substrate material.
In this embodiment, the broadband antenna system of the present invention may further comprise a plurality of the at least one tapered feed point, and the distance between each of the plurality of the at least one tapered feed point around the circumference of the substantially cylindrical feed portion may be less than ½ wavelength of the highest frequency of operation.
a is a sectional view with cut-away of a biconical dipole element disposed in a cylinder, showing a vertically-disposed balun, as disclosed in Applicant's prior U.S. Pat. No. 7,339,542.
b is a perspective view of a modified biconical dipole element with coneless cylindrical dual feed elements and a horizontally-disposed balun, according to an embodiment of the present invention.
c is a perspective view with cut-away of a modified biconical dipole element with coneless cylindrical dual feed elements and a vertically-disposed balun, according to an embodiment of the present invention.
d is a perspective view of a modified biconical dipole element with coneless cylindrical dual feed elements and an integrated wraparound balun, according to an embodiment of the present invention.
a depicts a graph, at 0.2 GHz, comparing the azimuth radiation patterns of a prior art monocone antenna with a modified monocone antenna system having a coneless cylindrical dual feed element according to a first embodiment of the present invention.
b depicts a graph, at 0.2 GHz, comparing the elevation radiation patterns of a prior art monocone antenna with a modified monocone antenna system having a coneless cylindrical dual feed element according to a first embodiment of the present invention.
a depicts a graph, at 0.45 GHz, comparing the azimuth radiation patterns of a prior art monocone antenna with a modified monocone antenna system having a coneless cylindrical dual feed element according to a first embodiment of the present invention.
b depicts a graph, at 0.45 GHz, comparing the elevation radiation patterns of a prior art monocone antenna with a modified monocone antenna system having a coneless cylindrical dual feed element according to a first embodiment of the present invention.
a depicts a graph, at 0.7 GHz, comparing the azimuth radiation patterns of a prior art monocone antenna with a monocone antenna system having a coneless cylindrical dual feed element according to a first embodiment of the present invention.
b depicts a graph, at 0.7 GHz, comparing the elevation radiation patterns of a prior art monocone antenna with a modified monocone antenna system having a coneless cylindrical dual feed element according to a first embodiment of the present invention.
a depicts a graph, at 0.95 GHz, comparing the azimuth radiation patterns of a prior art monocone antenna with a modified monocone antenna system having a coneless cylindrical dual feed element according to a first embodiment of the present invention.
b depicts a graph, at 0.95 GHz, comparing the elevation radiation patterns of a prior art monocone antenna with a modified monocone antenna system having a coneless cylindrical dual feed element according to a first embodiment of the present invention.
a depicts a graph, at 0.1 GHz, comparing the azimuth radiation patterns of a prior art biconical antenna with a modified biconical antenna system having coneless cylindrical dual feed elements according to a second embodiment of the present invention.
b depicts a graph, at 0.1 GHz, comparing the elevation radiation patterns of a prior art biconical antenna with a modified biconical antenna system having coneless cylindrical dual feed elements according to a second embodiment of the present invention.
a depicts a graph, at 0.18 GHz, comparing the azimuth radiation patterns of a prior art biconical antenna with a modified biconical antenna system having coneless cylindrical dual feed elements according to a second embodiment of the present invention.
b depicts a graph, at 0.18 GHz, comparing the elevation radiation patterns of a prior art biconical antenna with a modified biconical antenna system having coneless cylindrical dual feed elements according to a second embodiment of the present invention.
a depicts a graph, at 0.26 GHz, comparing the azimuth radiation patterns of a prior art biconical antenna with a modified biconical antenna system having coneless cylindrical dual feed elements according to a second embodiment of the present invention.
b depicts a graph, at 0.26 GHz, comparing the elevation radiation patterns of a prior art biconical antenna with a modified biconical antenna system having coneless cylindrical dual feed elements according to a second embodiment of the present invention.
a depicts a graph, at 0.34 GHz, comparing the azimuth radiation patterns of a prior art biconical antenna with a modified biconical antenna system having coneless cylindrical dual feed elements according to a second embodiment of the present invention.
b depicts a graph, at 0.34 GHz, comparing the elevation radiation patterns of a prior art biconical antenna with a modified biconical antenna system having coneless cylindrical dual feed elements according to a second embodiment of the present invention.
a depicts a graph, at 1.00 GHz, 1.37 GHz and 1.75 GHz, of the azimuth radiation patterns of a stacked collinear triple modified biconical antenna system having coneless cylindrical dual feed elements and a collinear generic element stacked on the upper biconical element, according to a seventh embodiment of the present invention.
b depicts a graph, at 1.00 GHz, 1.37 GHz and 1.75 GHz, of the elevation radiation patterns of a stacked collinear triple modified biconical antenna system having coneless cylindrical dual feed elements and a collinear generic device stacked on the upper biconical element, according to a fifth embodiment of the present invention.
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Although not shown, an alternate embodiment of the present invention may be a coneless monocone antenna system having a coneless monocone as described above in connection with
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Although not shown, an alternate embodiment of the present invention may be a frustum monocone antenna system having a frustum monocone as described above in connection with
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As embodied herein, the highest frequency of operation of the present invention may be determined by the number of feed points, the spacing between the feed points, and the diameter of the coneless feed region. This is expressed as
where fH=highest frequency of operation, n=number of feed points, c=speed of light, and D=diameter of feed region. Thus, the spacing between feed points should be at least 1/2λ of the highest desired frequency. Although not shown, the present invention contemplates that a plurality of feeds points, including but not limited to 3, 5, 6, 7, 8 or more, falls within the scope of the invention.
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As embodied herein, the foregoing balun configurations of
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It will be apparent to those skilled in that art that various modifications and variations can be made in the fabrication and configuration of the present invention without departing from the scope and spirit of the invention. For example, the design of the present invention contemplates one or multiple tapered feed points for the coneless radiator. While a preferred embodiment discloses two tapered feed points, three, four, five, six, seven or eight or more feed points are all considered within the scope of the invention. Because the highest frequency of operation is determined by the diameter of the coneless cylinder and the number of feed points, the diameter and number may be adjusted as desired for preferred frequencies.
As another variation, the coneless biconical element of the present invention may be incorporated with an asymmetrical dipole to form a monopole, thus providing an ultra-broadband antenna system of virtually infinite bandwidth. The cylinder of this variation may be formed from inexpensive G10 dielectric plastic (fiberglass) with copper cladding that is rolled into the cylindrical shape. The Duroid balun, which may also be an etched, microwave substrate with copper cladding, may be positioned along the center axis of the rolled G10 cylinder and fed at the tips of the etched features of the G10 board.
As another variation, two or three or more of the coneless biconical elements of the present invention may be stacked together, along with a high-gain omni-directional antenna at a given frequency band on top, and additional elements may be placed above and below the coneless biconical elements to cover additional frequency bands.
As another variation, the coneless biconical element of the present invention may be utilized in multiple frequency bands.
In addition, a variety of materials may be used to fabricate the components of the invention. For example, stealth materials, such as carbon-based compounds, may be used in order to reduce detection. The conductor surfaces may be replaced with frequency-selective surfaces whereby the surfaces act as conductors in selected frequency bands and also act as RF reactance (non-perfect conductors) at other bands.
As embodied herein, the antenna system of the present invention may be provided with any type of RF transceivers or transponders, such as radios, GPS receivers or radars; other antenna systems such as SATCOM; cameras, IR sensors, lights, and audio equipment; digital devices; as well as other electrical or mechanical devices operated by hydraulic, pneumatic or mechanical controls or actuators, or operated by a gas, liquid or solid material transfer system. Thus, the antenna system of the present invention may be used for a wide variety of applications in RF transmission and reception, navigation, communication, direction finding, radar, and electronic warfare. Thus, it is intended that the present invention cover the modifications and variations of the invention provided they come within the scope of the appended claims and their equivalents.
This application is related to and claims the benefit of prior-filed U.S. Provisional Application for Patent Ser. No. 61/064,725 filed on 21 Mar. 2008, entitled “MODIFIED CONICAL ANTENNA SYSTEM ALLOWING MULTIPLE STACKED COLLINEAR ELEMENTS,” which is incorporated herein by reference.
Number | Date | Country | |
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61064725 | Mar 2008 | US |