Antenna arrangement

An antenna arrangement 10 comprises a first elongate limb 12 and a second elongate limb 14. The first and second elongate limbs converge towards one another at a first electrical connection point 16 and a spaced anti-phase electrical connection point 18. The first and second limbs collectively forming a closed figure with a first appendage 22, a second appendage 24, a third appendage 26 and a fourth appendage 28 to the closed figure.

REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase of International Application PCT/IB2012/055827, filed Oct. 23, 2012, and claims priority to ZA Application No 2011/07758, filed Oct. 24, 2011. Each of the priority applications is hereby incorporated by reference in its entirety.

INTRODUCTION AND BACKGROUND

This invention relates to an antenna arrangement and to an antenna array comprising the arrangement, including a collapsible arrangement and array.

In radio direction finding applications, it is known to use loop-based Watson-Watt arrays or Adcock arrays. Loop-based Watson-Watt arrays are generally perceived to be inferior to Adcock arrays, mainly due to the inherent sensitivity of loop-based radiators to horizontal polarization (HP), which causes unavoidable estimation errors when the incoming wave is not purely vertically polarized (VP), and secondly, due to inaccuracy when waves are incident from high angles of elevation. These problems often come to the fore at low frequencies (in the HF band) with sky wave propagation, but not ground wave propagation. At higher frequencies, however, ground waves support appreciable HP and loops then suffer accuracy degradation due to cross-polarization making them unpopular for use in the upper HF and VHF regions and above. Adcock arrays suffer a disadvantage over loop elements from a sensitivity point of view when the arrays are small in size, which makes Adcock arrays less desirable for use in small tactical systems that are expected to work below 100 MHz.

OBJECT OF THE INVENTION

Accordingly it is an object of the present invention to provide an alternative antenna arrangement and array with which the applicant believes the aforementioned disadvantages may at least be alleviated or which may provide a useful alternative for the known arrangements and arrays.

SUMMARY OF THE INVENTION

According to the invention there is provided an antenna arrangement comprising:a first elongate limb and a second elongate limb;the first and second elongate limbs converging towards one another at a first electrical connection point and a spaced second anti-phase electrical connection point; andthe first and second limbs collectively forming a closed figure with first, second, third and fourth appendages to the closed figure.

In use, the first and second antenna arrangement connection points may be connected to first and second ports of electronic circuitry which are 180 degrees out of phase. The circuitry may comprise transmitter circuitry, so that the arrangement may act as a transmitting antenna arrangement. Alternatively, the circuitry may comprise receiver or detector circuitry, so that the arrangement may act as a receiving antenna arrangement.

Further alternatively, the circuitry may comprise both transmitter and receiver circuitry, so that the arrangement may act as a transceiving arrangement.

In one embodiment of the invention the closed figure and appendages are of an electrically conductive material and each of the appendages extends in spaced juxtaposition along a region of the closed figure adjacent thereto.

The closed figure may have any suitable shape, including but not limited to rectangular, square and rounded, such as elliptical or circular.

In another embodiment the first and second appendages form a first dipole and the third and second appendages form a second dipole.

In one form of this embodiment, the closed figure may be made of an electrically insulating material, so that the first dipole and the second dipole are spaced from one another adjacent opposite regions of the insulating closed figure.

In another form, the closed figure, the first appendage, second appendage, third appendage and fourth appendage are made of an electrically conductive material, so that there is provided a hybrid loop antenna comprising the closed figure forming a loop antenna and the first and second dipoles adjacent opposite regions of the loop antenna.

The antenna arrangement may comprise a first hinge and a second hinge connecting the first and second limbs to one another with the first hinge between the first and second appendages and the second hinge between the third and fourth appendages. A third hinge may be provided on the first limb between first and second hinges and a fourth hinge may be provided on the second limb between the first and second hinges, so that the arrangement is manipulatable between a first or deployed configuration and a second collapsed configuration wherein the first and second hinges are closer to one another than in the deployed configuration.

The closed figure may have any suitable shape such as rectangular, square, rounded, such as elliptical or circular or even a non-canonical shape. Similarly the appendages may also have any suitable shape such as rectangular, square, triangular, rounded, such as elliptical or circular or even a non-canonical shape.

The invention also includes within its scope an antenna array comprising a first arrangement as as herein defined and/or described and a second similar arrangement in mutually orthogonal relationship relative to one another and with each arrangement connectable to its respective electronic circuitry.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

In the diagrammatic representation inFIG. 1, an antenna arrangement which may form part of an antenna array, is generally designated by the reference numeral10. An example embodiment of the array is generally designated100inFIGS. 11 and 12.

Referring toFIG. 1, the arrangement10comprises a first elongate limb12and a second elongate limb14. The first and second elongate limbs converge towards one another at spaced first and second anti-phase antenna arrangement connection points16,18, so that the first and second limbs collectively form a closed figure with a first appendage22, a second appendage24, a third appendage26and a fourth appendage28to the closed figure.

InFIG. 2, one form of the antenna arrangement10is shown wherein the arrangement forms an alternative loop antenna. The closed figure and appendages22,24,26and28are made of an electrically conductive material and each of the appendages extend in spaced juxtaposition along a region of the closed figure adjacent thereto. For example, appendage24extends away from the connection point16in spaced juxtaposition relative to the adjacent region of the close figure towards point16. More particularly, the closed figure or loop20is circular and the appendage24is in the shape of a circle segment extending in spaced juxtaposition relative to adjacent circle segment region20.1of the loop20. The appendages may come close to each other at their free ends, but do not meet at their free ends. In this topology, the appendages22,24,26and28interact electromagnetically as parasitic elements with the conductor of the close figure.

It has been found that the embodiment is resistant to cross polarization, and the folding back of the appendages towards the closed figure makes it feasible to make a practical implementation of the antenna arrangement.

InFIG. 3, there is shown a more detailed implementation of the antenna arrangement ofFIG. 2. In this case, the closed figure or loop is square and the appendages22,24,26and28extend parallel to the respective adjacent sides of the loop. First and second sides20.1and20.2of the loop are formed by outer conductors of first and second coaxial cables21and23respectively, which are bridged at adjacent ends25. The centre conductors are connected at one ends thereof to electronic circuitry27(which in this example embodiment is receiver or detector circuitry, but it may also be transmitter circuitry or transceiver circuitry) having a first port29and a second port31which are 180 degrees out of phase. At their other ends, the centre conductors are connected to the anti-phase connection points16and18respectively. The third and fourth sides10.3and20.4of the loop are connected to the aforementioned centre conductors at connection points16and18, to form the loop. The first appendage22is connected to the outer conductor of the second coaxial cable23and the second appendage24is connected to the centre conductor of the second coaxial cable. The third appendage26is connected to the centre conductor of the first coaxial cable21and the fourth appendage28is connected to the outer conductor of the first coaxial cable21. Although shown on the outside of the loop20, the appendages may alternatively extend in spaced parallel relationship with the sides of the loop, on the inside of the loop.

When the connection points16and18are fed in anti-phase and the antenna is transmitting, or when the antenna is receiving signals and the received signals at the connection points16and18are subtracted from each other, the antenna behaves as a stable loop antenna over a wide range of frequencies providing the following performance advantages: a) improved cross polarization discrimination over a wider band than a normal loop antenna as shown inFIG. 4; b) resistance to practical manufacturing tolerances compared to current state of the art topologies; and c) improved gain performance over a conventional loop antenna of the same size, as shown inFIG. 5.

InFIG. 6there is shown a more detailed presentation of another form of the antenna arrangement10inFIG. 1. The first elongate limb12comprises a first linear and rigid part12.1and a second linear and rigid part12.2. The second elongate limb comprises a first linear and rigid part14.1and a second linear and rigid part14.2. The first antenna arrangement connection point16is at a first hinge where the first part12.1of limb12and the first part14.1of second limb14are hingedly connected to one another. The second antenna arrangement connection point18is at a second hinge where the second part12.2of limb12and the second part14.2of second limb14are hingedly connected to one another. The first and second parts of the first limb12are hinged together at third hinge34and the first and second parts of limb14are hinged together at fourth hinge36.

The arrangement is manually or automatically manipulatable between a first or deployed configuration and a second or collapsed configuration by manually manipulating the hinges34and36as shown at A between a first position wherein the connection points16and18are spaced form one another and a second position wherein the connection points are closer to one another than in the deployed configuration. It has been found that in at least some embodiments, the array functions as an antenna array throughout a substantial part of the continuously variable range of movement that the hinges and geometry allow between the collapsed and deployed configurations. However, it is expected that performance may degrade closer to the collapsed configuration.

Referring toFIG. 7, in some embodiments, the parts of limbs12and14collectively form the closed figure, namely parts12.12,14.12,14.21and12.21are made of an electrically insulating material whereas the parts12.11,14.11,14.22and12.22forming the appendages22,24,26and28are made of an electrically conductive material. In such embodiments, the arrangement10comprises two spaced dipole antennas30and32adjacent opposite regions of the closed figure.

In other embodiments, all of the parts of the limbs12and14are made of an electrically conductive material, so that the arrangement is a hybrid comprising a loop antenna20with the two spaced dipole antennas30and32adjacent opposite regions of the loop.

Referring toFIG. 8, in this embodiment there is provided an angle α of about 153° between the first and second parts of each of the first and second parts12.1and12.2of the elongate limb12. Similarly, the angle α is also provided between the first and second parts of each of the first and second parts14.1and14.2of the elongate limb14.

In one form of the embodiment ofFIG. 8, the parts12.12,12.21,14.21and14.12are about 145 mm in length. The appendages12.11,14.11,14.22and12.22are about 180 mm in length. When collapsed, the appendages12.11,14.11,14.22and12.22are parallel to one another. When deployed, the parts12.12,12.21,14.21and14.12are at 45° to the vertical and the first and second connection points16and18are about 204 mm apart.

A more detailed diagram of the electrical connections of the embodiment inFIG. 8is shown inFIG. 9and is self explanatory, when read with the description ofFIG. 3above.

InFIG. 10, there is shown in the solid line, a graph of sensitivity against frequency for the antenna inFIG. 9wherein all the parts12.12,12.21,14.21and14.12are made of a conductive material, to form a loop antenna20between the opposed dipoles. Also shown, but in dotted lines, is a similar graph for a prior art Adcock arrangement. An improved sensitivity at lower frequencies of the arrangement inFIG. 9is apparent. In another form of the embodiment ofFIG. 9, the appendages12.11,14.11,14.22and12.22are shortened to about 150 mm in length. The advantage of this configuration is that when collapsed, the dipoles30,32are only 30 cm high.

The antenna array100shown inFIGS. 11 and 12comprises first and second arrangements10.1and10.2as herein defined and/or described, arranged in mutually orthogonal relationship relative to one another. The dipoles30.1and32.1of the first arrangement10.1are diametrically opposite one another and the dipoles30.2and32.2of the second arrangement10.2are also diametrically opposite one another and orthogonally to the dipoles of the first arrangement. The arrangements10.1and10.2are each connectable via its connection points16.1,18.1and16.2,18.2to its respective electronic circuitry.

InFIG. 12the antenna array100is shown in the collapsed and portable configuration with only appendages22.1and24.1of arrangement10.1and appendages26.2and28.2of arrangement10.2visible.

It will be appreciated that the arrangement may alternatively be driven or fed in phase, thereby to create an omni-directional antenna arrangement.