Dipole Antenna Array

Abstract

An antenna array is disclosed for generating and directing a narrow beam or beacon of wave energy along a predetermined path. Illustratively, the antenna array includes a plurality of dipole elements disposed upon a substantially flat support member and connected by a distribution circuit through a single transition to an axial input cable. Significantly, the distribution circuit takes the form of an insulating member upon either side of which are disposed electrically conductive elements for establishing across the dielectric member a balanced conduit for the passage of high frequency signals (or waves) to each of the dipole elements. Further, the distribution circuit serves to divide and to appropriately distribute the input signal to each of the dipole elements of the array. A shell housing is disposed about the distribution circuit to provide in combination with the plurality of dipole elements an effective shielding therefore and also to provide a reflective surface to appropriately direct the discrete wave generated by each of the dipole elements.

Description

BACKGROUND OF THE INVENTION

1.Field of the Invention

This invention relates to antenna arrays for directing narrow beams or beacons of waves and more particularly to such antenna arrays composed of a plurality of dipole elements.

2. Description of the Prior Art

Radar and beacon antennas are frequently required to produce waves wide in one plane and narrow in the other, i.e., a "fan" beam. Such antennas may be used singly to produce a fan beam or may be stacked to produce a "pencil" beam. One of the most common antennas used today in the IFF beacon antenna which may be used for radar applications or for guiding aircraft. It is desired that such antennas generate a fan beam several degrees wide in azimuth and 30.degree.-60.degree. in elevation and polarized along its vertical axis.

In the prior art, such antennas have been constructed using a plurality of dipole elements or horns or combination thereof disposed in a linear array. Typically, each of the elements are energized by a suitable wave directed thereto by a wave guide, coaxial or stripline divider and suitable interconnecting lines. Typically, energizing waves in the microwave frequencies (e.g., in the order of 400 megacycles and above) may be directed along the coaxial cables to the antenna array. In order to convert the unbalanced energized signal as provided by the coaxial cable, to a balanced signal capable of being applied to the dipole elements, it is necessary to provide a transition to convert the unbalanced signal to a balanced one. Typically, the antenna arrays of the prior art have required a single converter, typically, known as a balun, for each dipole antenna. The resultant structure is not only very expensive but also proved to be noncompact and heavy, which characteristic negates its use for many applications including airborne radar systems.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a new and improved antenna array which does not require the use of apparatus for converting un unbalanced signal to a balanced signal for each dipole element of the array.

It is a further object of this invention to reduce the number and complexity of the parts interconnecting the dipoles, thereby increasing the overall reliability and reducing cost of the array.

It is a still further object of this invention to provide a new and improved antenna array which is not only light in weight and and compact, but also exhibits improved bandwidth characteristics.

The present invention achieves the abovementioned and additional objects and advantages by providing an improved antenna array comprising a plurality of dipole elements disposed upon a surface for radiating a composite wave formed from the discrete waves generated from each of the dipole elements. Significantly, each of the dipole elements is energized by a distribution circuit including a support member made of a suitable insulating or dielectric material, and first and second electrically conductive elements disposed on either side thereof for forming across the dielectric member a suitable conduit for the conduction of high-frequency signals to each of the dipole elements. By appropriately configuring the first and second electrically conductive elements, suitable signal energy distribution may be directed to each of the dipole elements to provide a composite wave of the desired configuration and direction. Further, a housing shell is disposed about the distribution circuit to not only shield the distribution circuit electrically but also to provide a reflective surface to appropriately direct the discrete wave generated from each of the dipole elements.

In an illustrative embodiment of this invention, the space disposed within the housing shell may be filled with a suitable insulating material to thereby provide a light-weight, structurally rigid antenna array.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention will become more apparent by referring to the following detailed description and the accompanying drawings, in which:

FIG. 1 is a perspective view of an antenna array incorporating a plurality of dipole elements in accordance with the teachings of the invention;

FIG. 2 is a perspective view partially broken away of a detailed, illustrative embodiment of the invention shown in FIG. 1;

FIG. 3 is a perspective view illustrating the distribution circuit used to energize the dipole elements of the antenna array shown in FIGS. 1 and 2;

FIG. 4 is a partially sectioned view of the distribution circuit and a dipole element as incorporated into the antenna array shown in FIGS. 2 and 1; and

FIG. 5 is a perspective view of a balun structure for connecting an input signal to an antenna array as shown in FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings and in particular to FIGS. 1 and 2, there is shown an antenna array 10 for generating and forming a composite beacon or beam 24 to be directed along a selected path. It is noted, that in radar applications this antenna could be used for not only transmitting the desired beam 24 but also receiving the reflected wave from the target. In an illustrative emobidment of this invention, the antenna array 10 includes a plurality of dipole elements or horns 12 disposed upon the surface of a support plate 14. In order to facilitate the generation of the beam 24 in a plane substantially perpendicular to the antenna array 10, it may be desirable to place the plurality of dipole elements 12 on the surface of a support plate 14; the surface of the plate 14 is made to conform as closely as possible to a plane. As illustrated in FIG. 1, each of the dipole elements 12 generates a discrete wave with a vertical polarization and that the discrete wave is combined with the other waves generated to form the composite beacon or beams 24. A distribution member 16 provides support for and forms a part of a distribution circuit 26 for distributing the signal energy derived from a single input and distributing the energized signals in a preselected manner to each of the dipole elements 12. As will be emphasized later, a shell housing 18 serves a variety of functions including: providing a cover and support for the antenna 10, providing a reflecting surface 20 for directing the discrete waves generated from each of the dipole elments 12 outward as is shown in FIG. 1 to form the composite beam 24, and to provide electrical shielding for a distrubution circuit 26.

With regard to FIG. 2, the details of an illustrative embodiment of this invention are more fully shown. It may be desired to generate a composite wave with a linear or planar phase front; to achieve this object, the dipole elements will be equally placed upon a uniform distance apart corresponding to a fraction of a wave length of the signal to be transmitted. The dipole elements are made of an electrically conductive material such as copper and may be formed upon the support plate 14 by suitable stamping operations or by suitable photolithographic etching techniques. The support plate 14 is made of a suitable insulating material such as fiber glass. It is noted that other more efficient dielectric materials may be used where higher frequency signals are to be applied to the antenna array 10. Further, a parasitic strip 40 made of a suitable material may be readily disposed between the dipole elements 12 to further control the beam 24. As in:icated in FIG. 2, the support plate 14 is connected to the shell housing 18 by a suitable sealing strip 32; the sealing strip comprises an epoxy adhesive which secures the tape backing, which may be made of fibre glass, to a flange 34 of the shell housing 18. The distribution member 16 is supported within the shell housing 18 by a pair of support brackets 30 which are secured as by spot welding to the floor of the housing shell 18. The distribution member 16 extends substantially perpendicular to the surface in which the dipole elements 12 are disposed, and in an electrical sense "invisible" to the vertically polarized field radiated from the dipole elements 12. Each end of the housing shell 18 is enclosed by a cover 36 which is connected to an edge portion of the shell housing 18 as by spot welding and to the support plate 14 by the sealing strip 32. In the process of assembly, the distribution member 14 may be disposed upon the support plate 16 and the conductive elements forming the distribution circuit 26 are electrically connected to each pole of the dipole elements 12 by a soldered joint 28. Finally, the unfilled space within the shell housing 18 may be filled with a suitable dielectric substance or support filter 38, taking the form in one illustrative embodiment of a polystyrene foam.

With referenc to FIG. 3, there is shown a significant aspect of this invention, wherein the distribution circuit 36 for transmitting a high-frequency signal as derived from an input terminal 62 to each of the dipole elements 12. In an illustrative embodiment of this invention, the antenna array 10 includes eight elements; it is apparent that many more elements could be incorporated into an antenna array in accordance with the teachings of this invention. In FIG. 3, essentially one-half of such an illustrative system is shown, depicting the distributing circuit 26 as it is coupled to four dipole elements 12; it is understood that the other four dipole elements of the array are similarly connected. Typically, it is desired to radiate waves from each of the dipole elements which are of the same phase. In order to accomplish this objective the electrical conduit from the input terminal to each of the dipole elements is made of substantially the same length. Further, it is desired to impart varying levels of power to each of the dipole elements 12 and in particular to provide less power to the elements disposed upon peripheral portions of the antenna array 10. By so "tapering" the power delivered to the dipole elements disposed on the extremities of the antenna array 10, the amplitude of undesirable side lobes will be decreased. Further, by insuring that the waves generated from each of the dipole elements 12 are of the same phase, the waves will tend to add to form a composite wave at the center plane of the antenna array 10 as indicated in FIG. 1. As shown in FIG. 3, the input terminal 62 is adapted to be connected to a coaxial cable for receiving and supplying to the antenna array 10 a signal of high frequency. Typically, coaxial cables transmit an "unbalanced" signal, whereas it is necessary to apply a "balanced" signal to each of the dipole elements 12. As referred to above, the prior art has sought to overcome this problem to providing a balun for converting the unbalanced signal to a balanced signal for each of the dipole elements 12, with the resultant disadvantages of cost and weight. In accordance with the teachings of this invention, only a single balun or conversion apparatus is required and it will normally be incorporated in the input terminal 62. Though not a part of this invention per se, the balun serves to convert an unbalanced signal to a balanced signal. There are many widely known types of balun. As shown in FIG. 5, a balun may illustratively comprise an input cable whose outer shield 64 has a slot therein extending along the axis of the cable for a distance of one-fourth the wavelength of the input signal. An axial conductor 66 is connected by a wire 67 to the outer shield 64. Further, the outer shield 64 and the axial conductor are connected by wires 68 to the first and second electrical elements 26a and 26b respectively of the distribution circuit 26. As discussed above, the distribution circuit 26 directs a balanced signal to each of the dipole elements 12.

With reference to FIG. 4, the distribution circuit 26 provides a conduit for a balanced signal. More specifically, it is noted that distribution circuit 26 includes the first and second conductive elements 26a and 26b disposed on either side of the distribution members 16 to provide a suitable conduit for the supply of a balanced signal to the dipole elements 12. In particular, the distribution circuit 26 includes a first branch 42 interconnecting the balun as illustratively shown in FIG. 2 to a first power dividing junction 44, which serves to distribute the energy to two further branches 48 and 46. The branch 48 directs the wave to a second power dividing junction 50 to distribute the wave along branches 52 and 54 to Jhe individual dipole elements 12. In a similar manner, the branch 46 is connected to a third power dividing junction 56 for distributing the wave along branches 58 and 60 to the separate dipole elements 12. The distribution circuit 26 has been carefully designed to provide in one illustrative embodiment of this invention the power dividing junctions 44, 50 and 56 to provide power distribution of values of -7.51 dB, -6.42 dB and -3.97 dB. The energy levels of the four dipole elements taken from the most central to the outermost elements 12 would be respectively 0 dB, -1.75 dB, -5.55 dB and -10.9 dB. Further, the distribution circuit 26 has been so designed as to provide a substantial impedance match between the branches 52, 54, 60 and 58 and their corresponding dipole elements.

A significant aspect of this invention resides in the multipurpose that the housing shield 18 serves. More specifically, it is desired that the distribution circuit 26 be shielded from outside electrical influences, and the housing shell 18 and the dipole elements 12 are disposed as to substantially surround the distribution circuit 26 with an electrically conductive shield. Further, the housing shell 18 provides the reflective surface 20 for directing the vertically polarized wave generated by the dipole elements along the desired path. Further, the housing shell 18 provides a ground plane to provide a ground or reference potential for the balanced signal conducted by the distribution circuit 26.

Thus, there has been shown an antenna array with significant advantages in terms of electrical performance, expense and weight over those devices of the prior art. Specifically, there has been shown an antenna array whereby the need for a plurality of baluns has been eliminated to thereby achieve a lighter, more compact structure. Thus, a greater number of the dipole elements may be disposed within a single array to thereby improve the band width performance and to more sharply define the generated wave or beacon.

Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description and shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

Claims

What is claimed is:

1. An antenna array for generating and directing a composite wave composed of a plurality of discrete waves, along a selected orientation, said antenna array comprising:

a plurality of dipole elements for radiating RF energy, mounted on a first insulating member with each of said dipoles comprising at least first and second conductors;

distribution circuit means, said distribution circuit means comprising at least first and second substantially identical patterns of electrical conductors, said patterns of electrical conductors being mounted on opposite sides of a second insuluting member, with said first and second patterns of electrical conductors being respectively connected to said first and second conductors which comprise said dipole elements; and

multipurpose mounting and shielding means for mounting said first and second insulating members at substantially right angles with respect to each other and for enclosing in combination said plurality of dipole elements said distribution circuit means to thereby electrically shield said distribution circuit means and for providing a reflecting surface for directing the radiation produced by said dipole elements to form a composite radiated wave.

2. An antenna array as claimed in claim 1, wherein said distribution circuit means provides an impedance match with each said dipole element.

3. The antenna array as claimed in claim 1, wherein said distribution circuit means provides unbalanced to balanced conversion means.

4. The antenna array as claimed inclaim 3, wherein said distribution circuit means provides balanced conduit paths to each of said dipole elements, said conduit paths being so configured as to reduce the energy level of the balanced signals directed to selected ones of said dipole elements.

5. The antenna array as claimed in claim 1, wherein said first insulating member is secured to said shielding means to form a unitary structure.

6. The antenna array as claimed in claim 1, wherein the spaced enclosed by said multipurpose shielding means and said plurality of dipole elements is filled with a dielectric substance.