AU723272B2

AU723272B2 - Low profile linear polarised antenna

Info

Publication number: AU723272B2
Application number: AU14709/97A
Authority: AU
Inventors: Noel A. Mcdonald
Original assignee: Radio Frequency Systems Pty Ltd
Current assignee: Nokia Services Ltd
Priority date: 1993-04-02
Filing date: 1997-02-17
Publication date: 2000-08-24
Anticipated expiration: 2013-04-02
Also published as: AU1470997A

Description

4.T P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990 4

S

0* *s*

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "LOW PROFILE LINEAR POLARISED ANTENNA" The following statement is a full description of this invention, including the best method of performing it known to us:- This invention relates to a modification of a device claimed and described in our Australian patent number 662611, hereunder referred to as the main patent, which claims an antenna array for transmitting or receiving a radio signal of a given wavelength, the array comprising at least one array section of a predetermined plurality of at least partial substantially symmetrical loops of elongated electrical conductive material serially interconnected by connecting section/s of elongated electrical conductive material, wherein respective axes of symmetry of adjacent loops are normal to each other, and wherein each loop has an arc length of approximately one given wavelength, and each connecting section has a length of approximately one 10 quarter given wavelength.

preferred embodiments described in the main patent, the feed point of the antenna is arranged such that current in the antenna elements will approximate a single travelling wave and radiation from the array will be nearly circularly polarised.

In one embodiment (Figure two wires, each forming a succession of connected S. 15 loops, carry currents outwards from the feed point towards open circuit ends of the wires. The feed is a balanced feed, that is, at an instant when one wire is driven positive relative to a ground plane, the other is driven negative. Therefore at an instant when the current is flowing into one wire from the feed point it is flowing out of the other wire at the feed point, giving a continuous current flow in the same direction 20 through the feed. The resulting spiralling current flow in the live wires is in the same sense of rotation, giving a corresponding spiralling or elliptically polarised radiation field.

Furthermore, in the main patent, the loops are of approximately one wavelength circumference, with a relative rotation of 90', and the lengths of the interconnecting conductors are approximately one-quarter wavelength.

It has been found that a more general relationship is possible in that successive loops can be rotated about their normal axes by an arbitrary angle provided that is also the electrical length, expressed as an angle, of the interconnecting conductors between those successive loops (one wavelength 360 electrical degrees). For example, a configuration of three serially connected loops having a relative loop rotation of 120' and interconnecting wires approximately 1200 long, i.e. a third of a wavelength.

It is an object of the present modification to provide an antenna array of the aforementioned kind in which successive loops are rotated about their normal axes by an arbitrary angle, to provide various configurations.

According to a first aspect of the modification, there is provided an antenna array for transmitting or receiving a radio signal of a given wavelength, said array comprising at least one array section of a predetermined plurality of at least partially, substantially symmetrical loops of elongated electrical conductive material serially interconnected by connecting section/s of elongated electrical conductive material, wherein respective axes of symmetry of adjacent loops are rotated by a predetermined angle that is greater or less than 900, and wherein each said loop has an arc length of approximately one said given wavelength, and each said connecting section has an electrical length, expressed as an angle, substantially equal to said predetermined angle of rotation of said adjacent loops.

It is an object of the present modification to provide an antenna array of the 15 kind having a linear polarised radiation field.

According to a further aspect of the modification, there is provided an antenna array as claimed in claim 1, wherein said antenna array includes signal input/output 9eg* feed means comprising at least one feed point located on the array such that, when said array is operatively associated with a ground-plane means, signal currents in the 20 array are caused to spiral away from said at least one feed point in opposite senses of rotation, whereby rotational components of radiation/radiating fields of the array cancel and thereby produce substantially linear non-rotating components.

The modified feed arrangement of the present invention is an unbalanced feed which causes currents in the array to spiral away from the feed point in opposite sense of rotation, so that the rotational components of its radiated fields cancel, leaving the desired linear, non rotating component.

In order that the invention may be readily carried into effect, embodiments thereof will now be described in relation to the accompanying drawings, in which: Figure 1 is a top plan view of a first configuration of radiating conductors &Z-cording to the invention.

i P Figure 2 is a top plan view of a second configuration of radiating conductors according to the invention.

Referring to Figure 1, the configuration comprises a planar array of four serially connected loops BCDEF, GHIJK, LMNOP and QRSTU of wire or other conductive material, each approximately one wavelength in circumference, the relative rotation of the loops is 90' and the electrical length of the interconnecting wires FG, KL, PQ and BU is also 900 being a quarter of a wavelength or the same length as one side of the loops. The wire configuration so formed is mounted approximately parallel to a planar conducting reflector, and a radio frequency voltage is injected or derived between feed point A and the adjacent planar reflector.

In operation, the radiation in a direction normal to the plane in which the conductors lie, from the currents in the conductors AB and AU will cancel as they are opposing, whereas the radiation in the same normal direction from the currents in the wires BC and UT is additive. Similarly the radiation in the normal direction from the currents in the wires DE and SR is additive, and more particularly as the loop 15 circumference is approximately one wavelength the radiation from DE and SR is additive to that from BC and UT. With the adjacent loops having a relative rotation of 900 and the interconnecting wires being approximately 90' long, it is found that the .i radiation from all wire sections BC, UT, DE, SR, HI, ON, JK, and ML are all additive in the direction normal to the plane of the loops, whereas the radiation in the same direction from most of the other wire sections cancels.

The feed at A can be replaced by dual feeds in the vicinity of B and U, or between B and U.

The wire at the point X opposite the feedpoint A can be opened with a gap, as from symmetry considerations no current will flow in the wire at the point.

Alternatively the wire at X can be connected to the ground plane either directly or through a load impedance.

The configuration can be fed at both A and X, each relative to the ground plane or relative to each other.

The feedpoint location A is not unique. For example feeding in the vicinity of D, in which case N will be the corresponding opposite point, will give similar desirable properties. In such a case the plane of polarisation of the radiation will be rotated by 450 compared with the case where A is the feedpoint, and instead of the radiation from several wire sections adding in the desired direction and from others cancelling, components of radiation from most sections are additive in the desired direction.

Referring to Figure 2, the configuration comprises a planar array of three serially connected loops BCDEFGH, IJKLMNO and PQRSTUV having a relative loop rotation of 1200 and interconnecting wires approximately 1200 long, or a third of a wavelength. Suitable feed points are at A or L.

The modified array described in the present specification is mounted as described in the specification of main patent No. 662611. As described in the main patent, the array may be mounted in a predetermined spaced relationship with a conductive ground plane element. The array of loops and interconnecting linear conductors may be mounted on a support base of insulating material and may be advantageously in the form of conductive tracks of a printed circuit board.

.:i The shape of the loops may be circular, square or polygonal, and may be oooo° partial loops, full loops or both.

15 The interconnecting conductors may be linear or curved.

oooo Although the improvement has been described in terms of a transmitting antenna, it will be understood that the improvement can be applied to a receiving antenna.

Further, as would be clear to those skilled in the art, the present antenna array 20 may be used as a sub-assembly in a larger array.

The antenna array of the present invention can be advantageously utilized in so-called wireless local loop telecommunication arrangements, a wireless local loop being an arrangement in which a radio link substitutes a twisted pair linking a subscribers telephone to a distribution pillar or the like in the street, thereby eliminating the need to run; cable across private property.

Claims

1. An antenna array for transmitting or receiving a radio signal of a given wavelength, said array comprising at least one array section of a predetermined plurality of at least partially, substantially symmetrical loops of elongated electrical conductive material serially interconnected by connecting section/s of elongated electrical conductive material, wherein respective axes of symmetry of adjacent loops are rotated by a predetermined angle that is greater or less than 900, and wherein each said loop has an arc length of approximately one said given wavelength, and each said connecting section has an electrical length, expressed as an angle, substantially equal to said predetermined angle of rotation of said adjacent loops.

2. An antenna array as claimed in claim 1, wherein said antenna array includes signal input/output feed means comprising at least one feed point located on the array such that, when said array is operatively associated with a ground-plane means, signal currents in the array are caused to spiral away from said at least one 15 feed point in opposite senses of rotation, whereby rotational components of radiation/radiating fields of the array cancel and thereby produce substantially linear non-rotating components.

3. An antenna array as claimed in claim 1 or 2, wherein said predetermined angle of rotation of adjacent loops is 1200, and wherein the electrical length of each ooo° 20 said connecting section is substantially

1200. °o

4. An antenna array as claimed in any one of the preceding claims, including a conductive ground-plane means arranged in a predetermined spaced relationship with said array.

5. An antenna array as claimed in any one of the preceding claims, wherein the symmetrical loops are full loops.

6. An antenna array as claimed in any one of claims 1 5, wherein at least one but not all loops are partial loops.

7. An antenna array as claimed in claim 1, comprising two said array sections.

8. An antenna array as claimed in any one of the preceding claims, wherein said 3~I trical conductive material is wire.

9. i An antenna array as claimed in claim 8, wherein said loops and said cting section/s of each array section are formed from a single length of said wire. An antenna array as claimed in any one of the preceding claims, wherein said loops and said connection section/s are co-planar. 11. An antenna array as claimed in claim 10, wherein said loops and said connecting sections are supported in an electrically insulated manner on a support means. 12. An antenna array as claimed in claim 11, wherein said support means is in the form of a planar panel. 13. An antenna array as claimed in any one of claims 1 to 7, wherein said loops and said connecting section/s are formed by a conductive track on a printed circuit board. 14. An antenna array as claimed in any one of the preceding claims, wherein said symmetrical loops are circular. An antenna array as claimed in any one of claims 1 to 13, wherein said 15 symmetrical loops are square or rectangular. coo• 16. An antenna array as claimed in any one of claims 1 to 13, wherein said symmetrical loops are polygonal. 17. An antenna array as claimed in any one of the preceding claims, wherein said connecting sections are straight. 20 18. An antenna array as claimed in any one of the preceding claims, wherein said 4.o. see loops and said connecting sections are integral. 19. An antenna array as claimed in any one of the preceding claims, operatively associated with another array. An antenna array substantially as herein described with reference to Figure 2 of the accompanying drawings. 21. An antenna array as claimed in any one of the preceding claims, operatively associated with a terminal of a satellite based mobile communications system. 22. An antenna array as claimed in claim 20, wherein said terminal is in the form of a portable suitcase terminal. N) -v Lu) 8 23. An antenna array as claimed in any one of Claims 1 to 20, operationally associated with a wireless local ioop telecommunications system. DATED THIS SECOND DAY OF JUNE 2000 RADIO FREQUENCY SYSTEMS PTY. LIMITED 004 686 097) .00 of** 9 a 1000