Patent Application
20060250315
The present invention relates to the field of antennas, and more particularly, this invention relates to small broadband antennas, and related methods.
Newer designs and manufacturing techniques have driven electronic components to small dimensions and miniaturized many communication devices and systems. Unfortunately, antennas have not been reduced in size at a comparative level and often are one of the larger components used in a smaller communications device. In those communication applications at below 6 GHz frequencies, the antennas become increasingly larger. In the 3 to 30 Mhz HF region for example, used by military, the proffered antennas become very large relative to operating platforms. A ¼ wave whip antenna for 5 Mhz is about 50 feet tall, and this is obviously unacceptable for use on a vehicle, and even fixed antennas require wire cage structures. It becomes increasingly important in these communication applications to reduce not only antenna size, but also to design and manufacture a reduced size antenna having a relatively broad gain bandwidth for a relatively small volume.
In current everyday communications devices, many different types of capacitor structures are used as antennas, which are the dipole antennas, the forms of which include the wire doublets, biconical dipoles, conical monopoles, discone antennas, and patch antennas. These are realized in a variety of different implementations. These antennas, however, are sometimes impractically large for the desired instantaneous bandwidth.
Conical antennas, which include a single inverted cone over a ground plane, and biconical antennas, which include a pair of cones oriented with their apexes pointing toward each other are used as broadband antennas for various applications, for example, direction finding. Referring to
Similarly, a single cone antenna includes a single antenna cone that also spans 360° and is symmetric about the cone axis. A single antenna cone is connected to an electronic coupler that provides a connection to a feeding circuit that provides an electrical signal to feed the antenna. The single cone antenna is located over a ground plane.
For example, U.S. Pat. No. 6,198,454 to Sharp et al. is directed to a broadband partial fan cone antenna. The antenna includes a radiator having a partial cone shape. U.S. Pat. No. 2,235,506 to Schelkunoff entitled “Ultra Short Wave Radio System”, describes the spheroidal and ellipsoidal geometries of single dipole doublets, having single resonant response. Multiple tuned responses, in which the antenna has a filter like polynomial response may be desirable in some applications.
Ultimately, there is a need for capacitive or dipole family antennas with greater instantaneous bandwidth, smaller size and stable beamwidth.
In view of the foregoing background, it is therefore an object of the present invention to provide a broadband dipole antenna with stable beamwidth over a frequency range.
This and other objects, features, and advantages in accordance with the present invention are provided by a dipole antenna including a first antenna element assembly and a second antenna element assembly arranged in a dipole antenna configuration. The first antenna element assembly includes at least one conical antenna element, and the second antenna element assembly includes a series of conical antenna elements with each successive conical antenna element at least partially within a prior conical antenna element. Preferably, the first antenna assembly also includes a series of conical antenna elements with each successive conical antenna element at least partially within a prior conical antenna element.
The series of conical antenna elements of the first and second antenna element assembly respectively comprise coaxially aligned conical antenna elements sharing a common apex, and may each include a same number of conical antenna elements arranged in a symmetrical pattern. Each of the first and second antenna dipole assemblies may further include a respective disk antenna element and/or a respective filament antenna element.
Preferably, outer edge portions of the first and second antenna element assemblies lie along a common imaginary spherical surface, and an antenna feed point is between the first and second antenna element assemblies, with the imaginary spherical surface being centered on the antenna feed point. A coaxial antenna feed includes an outer conductor connected to the first antenna element assembly, and an inner conductor connected to the second antenna element assembly. Also, each of the conical antenna elements may have a continuous conductive surface or be formed as a wire structure.
A method of making a dipole antenna includes arranging a first antenna element assembly and a second antenna element assembly in a dipole antenna configuration. Again, the first antenna element assembly includes at least one conical antenna element, and the second antenna element assembly includes a series of conical antenna elements with each successive conical antenna element at least partially within a prior conical antenna element. Preferably, the first antenna assembly comprises a series of conical antenna elements with each successive conical antenna element at least partially within a prior conical antenna element.
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternative embodiments.
Referring initially to
The series of conical antenna elements of the first and second antenna element assemblies 25, 21 respectively comprise coaxially aligned conical antenna elements sharing a common apex, and may each include a same number of conical antenna elements arranged in a symmetrical pattern. Preferably, outer edge portions of the first and second antenna element assemblies 25, 21 lie along a common imaginary spherical surface S, and an antenna feed point F is between the first and second antenna element assemblies, with the imaginary spherical surface being centered on the antenna feed point. A coaxial antenna feed 30 includes an outer conductor 31 connected to the first antenna element assembly 25, and an inner conductor 32 connected to the second antenna element assembly 21. Also, each of the conical antenna elements may have a continuous conductive surface, such as a copper sheet, or be formed as a wire structure.
Referring now to
A method of making a dipole antenna includes arranging a first antenna element assembly 51 and a second antenna element assembly 41 in a dipole antenna configuration. Again, the first antenna element assembly 51 includes at least one conical antenna element 54, 56, 58, and the second antenna element assembly 41 includes a series of conical antenna elements 44, 46, 48 with each successive conical antenna element at least partially within a prior conical antenna element. Preferably, as shown, the first antenna assembly 51 also comprises a series of conical antenna elements 54, 56, 58, with each successive conical antenna element at least partially within a prior conical antenna element. Conical antenna elements 54, 56, and 58, may be said to be “nested” inside other.
An advantage of the present invention is the enhancement of antenna bandwidth. Multiple tuned antenna responses, of like kind to the polynomial responses of analog RF filters, occur when elements 54, 56, and 58, are slightly offset in size. For instance, enhanced bandwidth can be obtained from multiple nested cones, where each cone is analogous to filter pole.
Multiple tuning of the biconical antenna is particularly beneficial when the antenna mechanical envelope is not spherical or elliptical, such as would occur if the antenna is fit into a tall cylindrical radome of a small diameter. Such mechanical envelopes force the cones to be of small diameter and their individual bandwidth is therefore narrow. The second harmonic VSWR spike of a tall thin biconical antenna has been controlled by the addition of a second pair of nested coaxial cones tuned for this purpose.
The multiple tuning feature of the present invention is especially beneficial for small cones of large flare angle, where the cones approximate or become flat discs. The
The invention is not so limited, as to require Tchebyschev polynomial frequency response, and the invention may be configured to provide, for example, a Butterworth polynomial response to eliminate passband ripple, and to reduce group delay or differential phase. Multiple tuning, in the present invention, can provide up to a 3π enhancement of antenna bandwidth, relative to single tuned biconical antennas, as described by Harold Wheeler in the paper “The Wide Band Matching Area For A Small Antenna”, IEEE Transactions On Antennas and Propagation, Vol. AP-31, No. 2, March 1983, pp 364-367. Multiple tuning in the present invention is analogous to the multiple modes described in “Physical Limitations In Omni-Directional Antennas”, L. J. Chu, Journal Of Applied Physics, Volume 19, December 1948, pp 1163-1175.
The polarity of successive nested cones also may be alternated to provide a sleeve monopole effect to the conical antenna system. That is, each successive nested cone may be fed 180 degrees out of phase with respect to each other.
The disc structures, 50 and 52 of
The
This invention includes a method for designing dipole type antennas.
There are, of course, many different types of bandwidth, including pattern bandwidth as pattern Beamwidth over frequency. The present invention allows the control of pattern beamwidth over frequency, when the nested cones are of successive size to “shed” the fields, such that the waves divorce from the cones are regular intervals in frequency.
In another embodiment, this invention may use antenna element assemblies 48 and 58, of
Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.
