Conformal Array Beam Forming Network

Abstract

A beam forming network is disclosed interconnecting one of a plurality of input terminals with a corresponding number or a different number of antenna elements of an antenna array. The beam forming network may be used in conjunction with such an antenna array to receive waves and to provide outputs corresponding thereto, or to radiate waves in response to a selected input signal properly applied. More specifically, each of the plurality of terminals which serve as output ports when receiving and input ports when transmitting, is coupled by a plurality of delay lines to each of the antenna elements. In a radiating system, a signal is applied to one of the input terminals which is coupled to each of the antenna elements through such delay elements that the waves radiated from each of the antenna elements are delayed by specified amounts which cause the direction of the composite wave or beam formed by the waves derived from all antenna elements to be directed along a line disposed at a particular angle with respect to the axis of the antenna array. In one embodiment of this invention, the antenna elements may be disposed in a linear array, which allows selection of beam directions in a plane containing the line of radiating elements, whereas in other embodiments of this invention, the antenna elements may be disposed in two or three-dimensional arrays, which allows selection of beam directions representing various combinations of azimuth and elevation angles relative to the array axis.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to antenna systems and in particular to beam forming networks associated therewith for coupling the antenna array to a set of terminals.

2. Description of the Prior Art

Phased array antennas are well-known in the art for radiating a wave about an axis having a selected angle with respect to the axis of the antenna array. Typically, such antenna arrays comprise a plurality of antenna elements mounted along a straight line or distributed over a plane. The direction of wave radiation with respect to the antenna axis is determined by the relative phases imparted to the signals applied to each of the antenna elements.

This invention is particularly related to the matrix circuitry coupled to either a linear, planar or three-dimensional array, for supplying signals to each of the antenna elements whereby a composite wave therefrom is directed along a chosen direction with respect to the axis of the antenna array. In the prior art, as shown in FIG. 1, a matrix, commonly known as a "Butler" matrix, is connected to a linear array of elements. In particular, the Butler matrix includes a plurality of input ports (or terminals) designated 10a to 10 h. Successive pairs of the input ports 10 are connected to 3db couplers 12 whereby signals from those couplers are applied selectively to a set of phase shifters 14a to 14d. In turn, the output of the phase shifters 14a to 14d and couplers 12a to 12d are connected selectively to a second set of 3db couplers 16a to 16d. Outputs of the 3couplers 16a to 16d are connected to a second set of phase shifters 18a to 18d whose outputs, in turn, are applied to a third set of 3db couplers, along with some outputs of the second set of couplers. By selectively choosing the phase shifts imparted by the first and second sets of phase shifters 14 and 18, the signals to be applied to each of the antenna elements are selectively phase shifted. More specifically, the outputs of the couplers 20a to 20d are applied through corresponding RF amplifiers 22 and isolators 24 to an array of antenna 3db elements 26. As shown in FIG. 1, a different one of the RF amplifiers 22 is coupled to each of the antenna elements 26a to 26h, which are disposed in a uniformly spaced linear array. By selectively applying a signal to one of the input ports 10a to 10h, a corresponding composite wave or beam will be radiated from the antenna elements 26a to 26h along a direction at a selected azimuth angle with respect to the axis of the antenna array. For example, if an input signal is applied to the input port 10a, a composite wave or beam will be directed from the antenna elements at an azimuth angle with respect to the axis of the antenna array indicated by the number "5" and whose wave is identified by the designation 28a. In a similar manner, each input port 10a to 10h corresponds to a composite wave identified by one of the numbers 28a to 28h having a similar subletter. Note that each composite wave is equivalent to a beam which is shown in azimuth, and much broader and symmetrical about the plane, containing the axis of symmetry of the radiating elements, in elevation.

If a Butler matrix is to be designed for a narrow frequency band, the radiating elements are spaced with their centers approximately one-half wavelength apart. In a wide band system, such as one covering an octave, of course it is not possible to maintain the optimum phase relationship at all these frequencies and a compromise is necessary. In such an array system employing Butler matrices, the angles represented by directions in which the beams are directed relative to the normal or axis of the antenna array, tend to be inversely proportional to the frequency of the signal applied to the input ports 10. For this as well as other reasons, the performance of the Butler matrix tends to be dependent upon frequency. Further, the antenna elements coupled with a Butler matrix are located typically in a straight line and/or in a planar surface with uniform spacing between the elements of the antenna array. However, there are certain applications wherein because of space and weight requirements, it is difficult if not impossible to dispose or mount the antenna elements in a straight line and/or within a planar surface. For example, where it is desirable to dispose such an antenna array within an aircraft, it may not be possible to satisfy these mounting conditions. Since the Butler matrix operates to control the phase of the signals to be applied to the antenna array in a manner largely independent of frequency, the direction of the composite wave by the antenna array so attached is frequency-dependent and further, the antenna elements so coupled must be disposed with uniform spacing between elements in a straight line and/or a planar surface, thereby making such a Butler matrix unsuitable for certain applications. A further disadvantage of a Butler matrix is that the number of antenna elements is restricted to the number of input ports.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a matrix to be coupled with an antenna array whereby the antenna elements of the array may be disposed in a "conformal" array, i.e., on a surface that does not conform to either a straight line and/or a plane, and their number need not be equal to the number ports and their spacing need not be uniform.

It is a further object of this invention to provide a coupling matrix for an antenna array whereby the direction of the composite wave radiated therefrom is dependent not upon a selection of a port feeding input circuits producing appropriate phase shifts largely independent of frequency but rather upon the selection of a port feeding input circuit producing appropriate time delays.

In accordance with the teachings of this invention, these and other objects are met by providing a matrix network for coupling a plurality of ports or terminals to an antenna array. The selection of the port to which a signal is applied is dependent upon the direction of the composite wave (or beam) desired. More specifically, in one embodiment, the matrix network of this invention includes a plurality of sets of delay lines, each set coupled by a suitable power dividing means such as a manifold to one of a set of the ports. Each of a second set of manifolds is each coupled to a delay line of a different set of delay lines. In turn, each manifold of the second set is connected to an antenna element of the array. Significantly, in any one set of delay lines associated with one port, each delay line is constructed as required to impart a delay to the input signal whereby the signals radiated by each of the antenna elements have such phases that when added they provide a composite wave or beam radiated from the antenna array in a particular direction.

In a further embodiment, separate matrices may be used to feed separate rows of radiators. With these matrices in turn, fed by matrices to reduce the number of the delay elements and circuit complexity. The delays in the matrix network of this invention tend to be essentially independent of frequency, and the antenna elements may be arranged so that adjacent elements are not equidistant from each other and/or maybe disposed on a surface that does not conform to either a straight line or a plane. Such an equal spacing and/or displacement of the antenna elements from a straight line or a plane is compensated for effectively in accordance with the teachings of this invention by appropriately tailoring the delays imparted to the input signals by the delay lines.

In one embodiment of this invention, the antenna array may compose but a single row of antenna elements arranged in a straight line with adjacent radiating elements equal distant from one another, whereas in a further different embodiment of this invention, the antenna elements may be disposed on an irregular surface to form a three-dimensional array of elements in which adjacent elements are not equidistance from each other. In the latter illustrative embodiment, the matrix network may illustratively comprise a plurality of those networks as described in the previous paragraph whereby a signal applied to a single input of the network is distributed with appropriate delays to each element of the 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 accompanying drawings, in which:

FIG. 1 is a schematic drawing of a matrix network of the prior art;

FIG. 2 is a schematic drawing shown in perspective, of a beam forming matrix network in accordance with teachings of this invention particularly adapted for coupling a set of terminals to a single row of antenna elements; and

FIG. 3 is a schematic drawing of a further embodiment of this invention including a plurality of beam forming matrix networks for coupling a set of input terminals to an array of antenna elements disposed on a planar surface to provide a two-dimensional array.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With regard to the drawings and in particular to FIG. 2, there is shown a beam forming network in accordance with the teachings of this invention and particularly adapted for coupling a row of antenna elements 42a to 42h with a set of input/output ports 30a to 30h. It may be understood that the beam forming matrix network of this invention is suitable to receive waves and to provide an output signal at one of the ports 30a to 30h, dependent upon the direction of an input wave, as well as to accept a signal (S) for energizing the antenna elements 42a to 42h so that a composite wave or beam is radiated along a line at an angle with respect to the axis of the antenna array dependent upon which of the ports 30a to 30h the input energizing signal is applied to. In this latter case which involves the radiating mode of operation, an RF signal is applied to a selected one or more of the input ports 30a to 30h to produce an output wave of beam configuration along a selected direction in azimuth. The antenna array illustratively includes eight antenna elements 42a to 42h, each having a relatively low gain and being disposed in the order of one-half wavelength apart. A radiating or antenna element for the purpose of explanation is defined to include one or any group of antenna elements which are so connected that their combined input (or output) passes through one port and the total radiation pattern of that element or group of antenna elements cannot be varied as related to the signal at the one port. The RF signal is applied through a selected one or more of the eight input ports 30a to 30h to corresponding one(s) of a first set of manifolds 32a to 32h serving as signal interconnecting means. Each manifold of the first set is, in this illustrative embodiment, an 8:1 power divider that feeds an equal signal through eight different delay lines or elements 34. As shown in FIG. 2, the input manifold 32h comprises a plurality of couplers 32h.sub.1 to 32h.sub.7. For the sake of clarity, the couplers of each manifold are not shown, but are illustrated only for the single manifold 32h, now to be described in detail. The input signal applied to the port 30h is coupled to a coupler 32h.sub.1 which divides the power essentially equally between a second coupler 32h.sub.2 and a third coupler 32h.sub.5. In turn, the power is divided essentially equally by these couplers 32h.sub.2 and 32h.sub.5 to be applied, respectively, to couplers 32h.sub.3 and 32h.sub.4, and to couplers 32h.sub.6 and 32h.sub.7, whereby the power applied to the input port 30h is effectively divided into eight equal parts and applied to the delay lines 34h.sub.1 to 34h.sub.8. In an illustrative embodiment of this invention, the couplers employed could be considered from a functional point of view to be hybrid with their fourth port (not shown) terminated in a matched resistive load. These couplers may take the form of microstrip (or stripline) Wilkinson couplers, as described in IEEE Transactions on Microwave Theory and Technique in "A Class of Broad Band Three TEM-Mode Hybrid," E. J. Wilkinson, Vol. MIT-16, No. 2, pp 110-116, Feb. 1968. An advantage of incorporating Wilkinson couplers is that they are simple, non-critical structural devices that may be readily manufactured.

In the illustrative embodiment shown in FIG. 2, eight sets of delay lines 34 are provided, one set for each input port 30. More specifically, a first set of delay lines 34a is associated with the input port 30a. In a similar manner, the sets of delay lines 34b to 34h are associated respectively with input ports 30b to 30h. In particular, an input signal applied to the input port 30h is divided equally by the manifold 32h and applied to the set of delay lines 34h comprised of eight delay lines 34h.sub.1 to 34h.sub.8. In turn, a second set of manifolds 36, each coupled with one of the eight antenna elements 42, is associated with the sets of delay lines 34a to 34h. In particular, the manifold 36a is comprised of a plurality of couplers 36a.sub.1 to 36a.sub.7 for coupling the signal transmitted through the delay lines 34a.sub.1, 34b.sub.1 -34h.sub.1 to the antenna element 42a. As shown in FIG. 2, sets of RF amplifiers 38a to 38h and isolators 40a to 40h are provided, with a single RF amplifier 38 and isolator 40 interconnected between a single antenna element 42 and one of the second set of manifolds 36. In particular, the output of the manifold 36a is coupled through the RF amplifier 38a and the isolator 40a to an antenna element 42a; it is understood that each of the other manifolds 36b to 36h are coupled, respectively, through corresponding RF amplifiers and isolators to antenna elements 42b to 42h.

The delays of each delay element 34 are selected to be of a value so that the relative phase of the signals applied to the equally spaced antenna elements 42, are such that waves radiated by all eight elements add in-phase to provide a composite wave or beam radiated in a horizontal direction at various azimuth angles. If the RF amplifiers 38 are operated in their linear region, a signal fed to one of the input ports 30 independently produces a composite wave producing a beam shape directed along a line dependent upon which of the input ports 30 the signal is applied to. Though, significantly, the beam forming network of this invention is not limited to operation with antenna elements disposed in a linear array, for purposes of simplifying its explanation, the operation of the beam forming matrix network will be explained for the illustrative example where the antenna elements 42 are disposed in a linear array. If an input signal is applied to the input port 30d and the delay imparted by each of the delay lines 34d.sub.1 to 34d.sub.8 is substantially equal, energizing signals essentially in-phase with each other will be applied to the antenna elements 42a to 42h, whereby a composite wave or beam will be directed substantially along the axis of the antenna array, i.e., the zero degree line shown in FIG. 2. However, if it is desired to direct the composite beam along a line, e.g. a line disposed at an angle of approximately 60.degree. with respect to the array axis, an energizing signal is applied to the input port 30h and the delays of delay lines 34h.sub.1 to 34h.sub.8 decrease in a linear manner with delay line 34h.sub.1 being the smallest and 34h.sub.8 being the largest. As a result the signals applied to the antenna elements 42a to 42h produce a composite wave or beam radiated along a line having an angle of approximately 60.degree. with respect to the axis of the antenna array.

As discussed above, the matrix circuits of the prior art and in particular, a Butler matrix, require that the antenna elements fed directly to them are located in a straight line with uniform spacing between the elements. However, in accordance with the teachings of this invention, deviations from such an ideal arrangement where the antenna elements are disposed uniformly spaced in a linear array, are readily compensated for by varying the delays of the delay lines. As a result, in those applications where antenna elements cannot be placed in a linear array, the antenna elements may be disposed on an irregular surface with or without uniform spacing and the values of the delay lines 34 are varied selectively to compensate for the physical location of its corresponding antenna elements. Since the matrix network employs time delays, the directions of the beam peaks are essentially independent of frequency. On the other hand, if devices producing phase shifts tending to be independent of beam frequency were employed the direction of the beam would vary as the frequency of the input signal varies.

Losses encountered in the matrix network of this invention have been estimated to be in the order of 9db greater than that encountered by the Butler matrix. This additional loss is not considered to present a serious problem since the beam forming network of this invention operates at a relatively low signal level and with system performance fixed; this loss may be compensated for by an additional 9db gain in the RF amplifiers 38 and/or an increase in the input signal level without affecting the amplifier output power required, which is an important parameter in the amplifier specification.

Further, the beam forming matrix network of this invention is particularly adapted to be constructed utilizing known techniques to provide a relatively small, easily manufactured assembly. In particular, the delay elements may be formed of reasonable lengths of suitable coaxial cable without connectors or with connectors for additional flexibility. Because of the relatively low power levels contemplated, the cables may be of relatively small diameter such as 0.034 inches and may be disposed in a compact configuration, especially so if connectors are not used. Even a greater reduction in size and cost and an increase in reliability may be realized by the use of microstrip (or stripline) delay lines integrated into the manifolds. In particular, the required delays may be distributed throughout the manifolds such that individual portions of those delay elements could be employed to produce a portion of the required delays in the signals to more than one radiating element.

The matrix network of this invention is not only applicable to an antenna array comprised of a single row of antenna elements, but also to those antenna arrays comprised of a plurality of antenna elements disposed in columns and rows and in particular, to those antenna arrays wherein the elements are disposed in a three-dimensional array on an irregular surface to provide a composite wave or beam controllable in azimuth and/or elevation. In FIG. 3, an illustrative embodiment of this invention is shown comprising a plurality of beam forming matrix networks 52, 54, 56 and 58 for coupling a plurality of terminals or input/output ports 50a to 50d to a like number of antenna elements 70a to 70d capable of being disposed in a non-planar surface. For the sake of clarity, only a limited number of antenna elements has been shown; it is understood that a large number of such antenna elements may be coupled to a matrix network system similar to that as shown in FIG. 3. The antenna elements 70a to 70d are disposed in horizontal rows and vertical columns with equal spacing between the rows and columns and are each connected to a corresponding one of the isolators 57a to 57d and of the amplifiers 59a to 59d. In the illustrative example as shown in FIG. 3, the number of antenna elements in each row equals the number in each column and the total number n equals the total number of different independent beams that can be radiated by feeding a signal(s) to a selected terminal(s), which also equals n in number. The number of matrix networks are indicated by the value 2.sqroot.n. However, in practice, the number of radiating elements in each row does not necessarily have to equal the number in each column and the number of beams does not necessarily equal the number of radiating elements. Of course, the number of matrix networks and the number of input terminals of such a system must be appropriately changed. It is contemplated within the teachings of this invention that the antenna elements 70 could be of a much larger number than that shown in FIG. 3 and could be disposed to cover an area other than rectangular, on an irregular surface with unequal spacings between the adjacent antenna elements. The beam forming matrices serve, in a manner similar to that described with regard to FIG. 2, the purpose of receiving an input signal and for dividing that input signal into a number of output signals selectively delayed.

In the illustrative example of FIG. 3, the matrix networks 52, 54, 56 and 58 serve, in a radiating mode, to divide the input signal applied to one input port 50 into four substantially equal signals delayed selective amounts to be applied to each of the antenna elements 70. In an illustrative embodiment of this invention, the matrix network 52 includes a power divider 60b associated with the input port 50b for dividing the input signal and for applying the divided input signal to delay lines 62d and 62c. In a similar manner, the input signal applied to the port 50a is divided by divider 60a and applied to delay lines 62a and 62b. The delayed signals derived from the delay lines 62c and 62a are coupled by a divider 64a to be transmitted along line 66a to a similar matrix network 58, whereas the output signals of delay lines 62b and 62d are applied by a divider or manifold 64b along a line 66c to a matrix network 56. By employing a plurality of the matrix networks similar to that of matrix network 52, a signal applied to one of the ports 50 is divided and delayed by selective amounts to be applied, in turn, through an RF amplifier with or without an isolator to each of the antenna elements 70a to 70d to radiate a wave or beam in the shape of a beam along a line displaced from the axis of the antenna array. In FIG. 3, the waves are depicted in a highly idealized form wherein an input signal applied to a terminal 50 identified by a particular letter causes an output wave producing a beam indicated by a similar letter to be radiated from the antenna array. Of course, when this system is employed for receiving, the signal derived from one of the ports 50 is indicative of a received wave from an emitter with a receiving beam identified by the same letter.

Thus, there has been shown a matrix network specially adapted to be used in a receiving or radiating antenna system whereby the antenna elements may be disposed in an array not limited to a linear or planar configuration, but wherein the antenna elements may be disposed with an equal spacing on an irregular surface and the element displacement from the ideal compensated for by tailoring the values of time delay imparted by the time delay elements of the matrix network.

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

Claims

What is claimed is:

1. A matrix network for intercoupling a plurality of terminals and a plurality of antenna elements disposed in an antenna array having any suitable axis, said matrix network comprising:

a. a plurality of sets of fixed time delay means;

b. a first set of signal interconnecting means including a plurality of power dividers forming a first corporate feed, each for interconnecting one of the said terminals and each of said delay means of one of said sets; and

c. a second set of signal interconnecting means including a plurality of power dividers forming a second corporate feed, each for interconnecting at least one delay means of each set of said plurality of sets and one of said antenna elements, whereby a signal present at one of said terminals corresponds to signals at each of said antenna elements;

d. each delay means imparting a time delay to a signal passing therethrough, selected such that a beam oriented in a selected direction with respect to said axis of said antenna array is associated with one of said terminals.

2. A matrix network as claimed in claim 1, adapted to radiate a composite beam from said antenna array along the selected direction with respect to said antenna axis of said array dependent upon which of said terminal elements an energizing signal is applied.

3. A matrix network as claimed in claim 2, wherein the delay of each of said delay means is selected to impart relative phasing to the signals applied to said antenna elements such that the waves radiating from each of said antenna elements adds in-phase to provide the composite beam in the selected direction.

4. A matrix network as claimed in claim 3, wherein each of said signal interconnecting means of said first set divides the energizing signals applied to said terminals substantially equally and applies substantially equal signals to said delay means of its corresponding set of delay means.

5. A matrix network as claimed in claim 1, wherein selected of said antenna elements are displaced from a planar surface by varying amounts, and the time delays imparted by said delay means are selected to compensate for the positional variations of said antenna elements from said planar surface.

6. A matrix network as claimed in claim 1, wherein said antenna elements are disposed in a row.

7. A matrix network as claimed in claim 5, wherein there is included amplifier means interconnected between one of said signal interconnecting means of said second set and one of said antenna elements.

8. A matrix network as claimed in claim 1, wherein there is included amplifier means interconnected between one of said signal interconnecting means of said second set and one of said antenna elements.

9. A matrix network as claimed in claim 8, wherein isolator means is interconnected between one of said amplifier means and one of said antenna elements.

10. A matrix network as claimed in claim 1, wherein said signal interconnecting means comprises a manifold.

11. A matrix network as claimed in claim 1, wherein said antenna elements are disposed in an array of columns and rows of antenna elements, said plurality of sets of fixed time delay means including first and second groups of said sets, said first set of signal interconnecting means interconnecting one of said terminals to each of said delay means of one set of said first group, a third set of interconnecting means interconnecting a delay means of each set of said first group to each delay means of a set of said second group, and said second set of signal interconnecting means interconnecting at least one delay means of each set of said second group and one of said antenna elements.

12. A matrix network as claimed in claim 11, wherein said rows and columns of elements are disposed in a two-dimensional array.

13. A matrix network as claimed in claim 11, wherein said antenna elements are disposed in a three-dimensional array, and the time delay imparted by each of said time delay means is fixed at an amount in accordance with the position of each antenna element within said three-dimensional array to orient a beam with respect to said three-dimensional array such that a signal present at one of said terminals is associated with a single beam oriented selectively with respect to said array axis.

14. A matrix network as claimed in claim 1, wherein each of said antenna elements is disposed in a row and is connected by said second set of interconnecting means of said second set to corresponding delay means of each set, the time delays imparted by said delay means of a first set increasing progressively in a first direction and of a second set increasing progressively in a second, opposite direction whereby at least two beams may be emitted from said antenna array at two different orientations thereto in response to input signals applied to first and second terminals coupled respectively by said interconnecting means of said first set to said first and second sets of delay means.

15. A matrix network as claimed in claim 11, wherein there is included amplifier means interconnected between one of said signal interconnecting means of said second set and one of said antenna elements.

16. A matrix network as claimed in claim 15, wherein isolator means is interconnected between one of said amplifier means and one of said antenna elements.