1. Field
Aspects of the present invention relate to antenna arrays, and particularly, collinear antenna arrays.
2. Description of Related Art
Collinear antenna arrays have many applications and are often used for aerodynamic applications. An exemplary collinear antenna array includes an array of dipole antennas mounted in such a manner that the corresponding antenna filaments of each antenna are parallel and collinear along a common line or axis. A collinear antenna array may be mounted vertically or horizontally in order to increase overall gain and directivity in the desired direction. However, placing a collinear antenna array in close proximity to its support structures typically results in a tradeoff between bandwidth and/or efficiency. Requirements for antenna arrays to be both compact and wideband generally oppose one another so that optimizing one requirement often negatively affects the other requirements. This is a particular problem for UHF and VHF antenna arrays in which wavelengths range from meters to tens of meters. Some applications such as an airborne platform cannot afford even a meter of added space to house a wideband antenna array on the vehicle or in an external pod. Prior antenna designs have been developed and have failed to meet the desired requirements, which are to be low profile, have a wide bandwidth, and have the ability to support frequency scan as required for a phased array sensor system.
Alford (U.S. Pat. No. 4,031,537) discloses an end fed array of collinear dipoles that can be placed less than a quarter wavelength from a host reflector, but have limited bandwidths. In addition, end fed arrays such as those disclosed in Alford are limiting in beam agility over bandwidth when used with phased arrays.
Canonico (U.S. Pat. No. 4,749,997) discloses a modular antenna array that overcomes the end feed limitation, with parallel fed elements that can be mounted in close proximity to the leading edge of a wing with the aid of collinear dipole elements and Yagi directors. Parasitic directors such as Yagi, or similar directors have the ability to guide energy away from a host, allowing a low profile installation, but Yagi type directors are known to have limited bandwidths.
Marino (U.S. Pat. No. 6,043,785) discloses a slot antenna arrangement that improves upon the limited bandwidth of parallel feed co-linear arrays by proposing flared notches with a balun. Likewise, Lee et al. (U.S. Pat. No. 5,841,405, co-invented by the Applicant and assigned to the same assignee of the instant application) teaches a collinear array of flared bunny ears with improved baluns for wide bandwidth; however both of these designs and similar notch elements often proposed for this type of problem suffer with large size due to their long radiators which are not often suitable for an integrated extreme low profile installation on a host platform.
Other parallel fed collinear antenna arrays such as those disclosed by Kaegebein (U.S. Pat. No. 6,057,804) attempt to solve the above problem with designs capable of tunings over a broad band, but with operating bands relatively small compared to the proposed antenna arrays of the present invention. Apostolos et al. (U.S. Pat. No. 6,839,036) is yet still another attempt to tune a broadband notch element for lower profile operation, but even this design is only of minor improvement.
Still other planar arrays such as an antenna arrays using long slot apertures as disclosed by Livingston et al. (U.S. Pat. No. 7,315,288), which is a “current sheet antenna,” have been shown to be both wideband and low profile, but all such examples require a 2-dimensional array of elements with a square footprint of at least ½ wavelength. In many cases these larger footprints would be too large in one dimension to mount on an aircraft wing or inside an aerodynamic pod for the lower UHF and VHF frequencies.
In all prior attempts known to the Applicant to solve the above discussed problems, the lattice spacings are held to be approximately within the range of a quarter to half wavelengths. However, denser packing lattice is still desired.
Aspects of embodiments according to the present invention are directed toward a novel Continuous Current Rod Antenna that may be fabricated by coupling an array of collinear antenna elements in close proximity to a conductive backplane that is optionally covered with an RF absorber, or meta material. The Continuous Current Rod Antenna has extremely tight lattice which stabilizes the radiation impedance and allows dense T/R modules packaging. A current filament is excited by connecting parallel fed collinear currents and matched by the novel technique using a high dielectric sleeve. The Continuous Current Rod Antenna offers lower profile packaging, with higher gain over larger bandwidths than other collinear array techniques. It is also possible to connect as many transmitter modules as possible to an antenna array for combining power output optically which in turn lowers the output requirement for any one module, as to share the transmit power output between a large number of modules.
According to an embodiment of the present invention, an antenna array includes: a dielectric sleeve extending in a first direction; at least two parallel fed radiator filaments collinearly arranged in the first direction within the dielectric sleeve, the radiator filaments being electrically connected to each other; and a conductive backplane spaced from the radiator filaments by ⅛ wavelength or less of a center operating frequency of the antenna array.
According to an embodiment of the present invention, an antenna array includes: an array of feed lines extending in a first direction; a dielectric sleeve extending in a second direction; at least two radiator filaments configured to be fed in parallel with each other by respective feed lines of the array of feed lines, the radiator filaments collinearly arranged in the second direction within the dielectric sleeve; and a conductive backplane spaced from the radiator filaments by ⅛ wavelength or less of a center operating frequency of the antenna array.
According to an embodiment, a combined length of the radiator filaments in the first direction may be at least about ½ wavelength of the center operating frequency of the antenna array.
According to an embodiment, a cross-section of the dielectric sleeve may have a diameter about 1/100 wavelength of the center operating frequency of the antenna array, and may have a permittivity (Er) of about 40 or greater.
According to an embodiment, wherein the cross-section of the dielectric sleeve may have a round shape or a square shape.
According to an embodiment, the dielectric sleeve may include a low loss high dielectric material such as ceramic magnesium titanate.
According to an embodiment, the antenna array may further include an RF absorber on the conductive backplane. The RF absorber may include a ferrite material having high real permeability and low imaginary permeability.
According to an embodiment, a center-to-center distance between adjacent ones of the radiator filaments may be about 1/20 wavelength or less of the center operating frequency of the antenna array.
According to an embodiment, the antenna array may further include an array of transmission lines respectively connected between the radiator filaments and the backplane.
According to an embodiment, each of the radiator filaments may have a first end and a second end respectively connected to two adjacent transmission lines of the array of transmission lines.
According to an embodiment, the antenna array may further include a plurality of transmit/receive (T/R) modules respectively connected to the radiator filaments via the array of transmission lines. The plurality of T/R modules may be configured to drive the radiator filaments without the use of a balun.
According to an embodiment of the present invention, an antenna system includes: a dielectric sleeve extending in a first direction; a plurality of parallel fed radiator filaments collinearly arranged in the first direction within the dielectric sleeve, the radiator filaments being electrically connected to each other; a conductive backplane spaced from the radiator filaments by ⅛ wavelength or less of a center operating frequency of the antenna array; and a plurality of transmit/receive (T/R) modules respectively electrically connected to the radiator filaments.
These and/or other aspects of the present invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
a-7f illustrate calculated unit cell H-plane element patterns of the Continuous Current Rod Antenna according to an embodiment of the present invention.
a-8d illustrate active input VSWRs for broadside array in different E plan scans.
a illustrate a comparative notch antenna according to the related art.
b illustrates a Continuous Current Rod Antenna according to an embodiment of the present invention and two comparative examples of notch antennas, and their corresponding graphs illustrating their realized gain.
Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects of the present invention.
Aspects of the present invention are directed toward wideband and low frequency collinear phased array antennas which may be mounted parallel and in close proximity to host structures such as a building, automobile, and more specifically on an aircraft. Aspects of the present invention are directed toward a Continuous Current Rod Antenna that is described herein as an array of parallel fed electrically connected collinear antenna filaments (or radiator filaments). This novel antenna design provides a compact solution with an order of magnitude greater gain and bandwidth compared to the state of the art. In addition, the volume problems that often plague UHF & VHF broadband antenna systems may be mitigated with an antenna design as shown in
Referring to
Further, each of the radiator filaments 100a may have a length in the second direction equal to substantially less than 1/20 wavelength. The parallel feed lines 100 may be spaced from each other in the second direction by substantially less than 1/20 wavelength. The radiator filaments 100a are excited in parallel via the parallel feed lines 100 (e.g., transmission lines). In one embodiment, the parallel feed lines 100 may be transmission lines fabricated on a printed circuit board as striplines or microstrips. In another embodiment, the parallel feed lines 100 may be coaxial cables extending substantially in parallel. According to the above embodiments, the Continuous Current Rod Antenna is mounted in close proximity to a conductive backplane support structure and can radiate over several octaves of bandwidth with high efficiency which has more bandwidth and gain over a wider band than the related art.
Referring to
In the above described embodiment, large bandwidths (e.g., 5:1 frequency ratio or greater) may be achieved. The key in achieving large bandwidths is the very tight lattice spacings that may be employed according to the present embodiment, which in turn allows dense packing of the T/R modules, thereby increasing the power output of the full system from a relatively small volume. Extremely tight lattices that may be achieved according to embodiments of the present invention are on the order of S= 1/100 of a wavelength at the lowest frequency and S= 1/20 wavelength at the highest frequency of operation. In
Since the reflection scattering from a backplane can interfere with radiation at some frequencies when covering a large bandwidth, backscatter from the conductive backplane 200 (e.g., a metallic backplane) may be minimized or reduced with an RF absorber 400 (shown in
According to the embodiment shown in
One of the goals of an antenna design is to transform the impedance to minimize the reactance of the device so that it appears as a resistive load. An “antenna inherent reactance” includes not only the distributed reactance of the active antenna but also the natural reactance due to its location and surroundings. Reactance is unwanted and diverts energy into the reactive field. According to an embodiment of the present invention, the impedance of the energy field from the current line running axially the length of the array of radiator filaments 100a can be transformed to a real value and matched to free space with low reactance by the dielectric sleeve 300, with a diameter about 1/100 wavelength with a permittivity of Er=40 or greater. The dielectric sleeve 300 may have a round or square shape cross-section, may be fabricated in a monolithic rod or blocks, and is slipped over the radiator filaments 100a. The dielectric sleeve 300 may be fabricated out of typical low loss high dielectric material such as ceramic magnesium titanate. However, the present invention is not limited to the above described embodiments, and the dielectric sleeve 300 may have other suitable shapes and may be fabricated out of other suitable dielectric materials.
Referring to
a-7f illustrate calculated unit cell H-plane element patterns of a Continuous Current Rod Antenna according to an embodiment of the present invention.
a-8d illustrate active input VSWRs for broadside array in different E plan scans (0, 30, 40, and 60 degrees).
As shown in
Some benefits of a Continuous Current Rod Antenna according to embodiments of the present invention will be demonstrated by the following comparative examples.
a and 9b illustrate a Continuous Current Rod Antenna according to an embodiment of the present invention and a comparative notch antenna, and their corresponding graphs illustrating their realized gain comparison.
In
As shown in
According to the above described embodiments of the present invention, a novel Continuous Current Rod Antenna may be fabricated by coupling an array of collinear antenna elements between an array of active RF T/R modules in close proximity to a conductive backplane that is optionally covered with an RF absorber, or meta material. Extremely tight lattices may be realized which stabilizes the radiation impedance and allows dense T/R packaging to aid in power generation. A current filament is excited by connecting parallel fed collinear currents and matched by the novel technique using a high dielectric sleeve. The Continuous Current Rod Antenna offers lower profile packaging, with higher gain over larger bandwidths than previously known by other collinear array techniques. It is also possible to connect as many transmitter modules as possible to an antenna array for combining power output optically which in turn lowers the output requirement for any one module, as to share the transmit power output between a large number of modules.
While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.
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Entry |
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Extended European Search Report for European Application No. 12168440.1, Filed May 17, 2012, Extended European Search Report dated Nov. 6, 2012 and mailed Nov. 13, 2012 (8 pgs.) |
Number | Date | Country | |
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20130038504 A1 | Feb 2013 | US |