WO2002084797A1

WO2002084797A1 - Antenna

Info

Publication number: WO2002084797A1
Application number: PCT/IB2002/001170
Authority: WO
Inventors: Marius Du Plessis; William Ian George; Pierre Steyn
Original assignee: Marius Du Plessis; William Ian George; Pierre Steyn
Priority date: 2001-04-12
Filing date: 2002-04-11
Publication date: 2002-10-24

Abstract

An antenna capable of creating a steerable circularly polarized directive beam is disclosed. It includes a plurality of circularly polarized radiator elements adapted to receive and emit electro-magnetic signals; a conductive base plane; and mounting means for each radiator element relative to the base plane. The antenna may include moving means adapted to rotate at least part of the radiator elements independently and angularly to obtain a phase shift relative to an unrotated radiator element or a differently rotated radiator element and the mounting means may be adapted to allow independent rotation of each radiation element relative to the plane.

Description

Antenna.

FIELD OF INVENTION

The present invention relates to an antenna.

More particularly, the invention relates to a phased array antenna with phase shifters or adjustment means for adjusting the signal phase associated with individual radiators.

BACKGROUND TO INVENTION

Antennas are designed to transmit and receive electro-magnetic waves.

Antennas for various purposes are continuously being further researched and developed.

A phased array antenna is an antenna with a directive radiation pattern which can be controlled by controlling the individual radiator elements or groups of radiator elements. In general, the steering direction of the directive antenna radiation pattern is determined by control of the phases of the signal to or from the radiator elements. The phase control is achieved by phase shifters which have the major requirements of low transmission loss, low cost, and in the case of transmission, capability to withstand high signal power. In addition the power consumption of the phase shifter must also preferably be low.

In particular in the field of aircraft antennas compactness is a major factor.

It is an object of the invention to suggest a new type of antenna with improved characteristics. SUMMARY OF INVENTION

According to the invention, an antenna capable of creating a steerable circularly polarized directive beam includes

a) a plurality of circularly polarized radiator elements adapted to receive and emit electro-magnetic wave signals;

b) a conductive base plane; and

c) mounting means for each radiator element relative to the base plane.

The antenna may include moving means adapted to rotate at least part of the radiator elements independently and angularly to obtain a phase shift relative to an unrotated radiator element or a differently rotated radiator element, and the mounting means may be adapted to allow independent rotation of each radiation element relative to the plane.

Also according to the invention, a phased array antenna includes

a) a plurality of radiator elements adapted to receive and transmit electro-magnetic signals, each radiator element being circularly polarized;

b) a conductive base plane;

c) mounting means for each radiator element mounting -it swivelably and/or rotatably relative to the base plane;

d) a feed structure adapted to transmit signals from and to the radiator elements and combining the signals to enable connection of the radiator elements to at least one coaxial connector; e) a plurality of rotating means adapted to independently rotate or swivel the radiator elements relative to the base plane, thereby varying the phase shift of the signal associated with each radiator element relative to another unrotated or differently rotated radiator element; and

f) electronic means adapted to control the rotating means and associated phase shift.

The mounting means may include a rotary joint.

The rotary joint may be adapted to make use of slip joints or non-ohmic capacitive coupling to achieve a low loss transmission means for the signal to or from a radiator element.

The antenna may be of modular construction.

The base plane may have a planar structure.

The base plane may be conformal (non-planar).

The base plane may have a circular circumference.

The base plane may have an elliptical circumference.

The base plane may be rectangular with rounded corners.

The feed structure may be made up of signal transmission line sections designed to achieve desired distribution of the signals to and from the radiator elements.

The Hne sections may be microstrip, stripHne or coaxial type feed structures.

A corporate or series feed structure, or combination thereof, may be used. The feed structure may connect all the radiator elements to a single coaxial connector for interfacing to coaxial cable or directly to associated communication equipment.

Each radiator element may be a helix radiator element.

The radiator element may be a circularly polarized radiator element consisting of a crossed dipole radiator, a spiral radiator, a microstrip patch radiator, a quadrafilar helix, or any other suitable radiator element.

Any two radiator elements may be adjusted to have up 180 degrees phase difference between them.

Each radiator element may include a conductive housing in which may be provided rotatably a conductive ground plane disc on which a feed network circuit is provided, a lower radiator metal disc, operatively connected by way of feed pins to the feed network circuit, mounted on the conductive ground plane disc, the housing being closed by an upper conductive radiator disc. In this case, only a portion of the rotating element is rotated to achieve a phase shift relative to an unrotated or differently rotated radiator element.

The upper radiator disc may be a cross-slot radiator disc.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described by way of example with reference to the accompanying schematic drawings.

In the drawings there is shown in:

Figure 1 a schematic representation of a linear, equispaced phased array antenna, with corporate feed, in accordance with the invention; Figure 2 a side view of a first embodiment of a radiator element included in the antenna referred to in Figure 1;

Figure 3 a plan view seen along arrow III in Figure 2;

Figure 4 a view from below seen along arrow IV in Figure 2;

Figure 5 a perspective view of the radiator element shown in Figures 2 to 4 when rotated;

Figure 6 a perspective view of the radiator element shown in Figures 2 to 4 when in unrotated condition;

Figure 7 a plan view of a second embodiment of a radiator element included in the antenna referred to in Figure 1;

Figure 8 a view from below of the radiator element illustrated in Figure 1; and

Figure 9 on an enlarged scale, a sectional side view of portion of the antenna seen along arrows IX-IX in Figure 8.

DETAILED DESCRIPTION OF DRAWINGS

Referring to Figure 1, an antenna in accordance with the invention, generally indicated by reference numeral 10, includes a number of radiator elements 12.1

... 12.5 operatively joined as shown. i i

The antenna 10 operates both as a receiving antenna as well as a transmitting antenna.

The incoming or outgoing radiation signals indicated by lines 14.1 ... 14.5 and the angle of these lines to the radiator elements 12.1 . .. 12.5 is indicated by the angle φ. Radiator element mounting structures (including rotary joints) 16.1 ... 16.5 are provided allowing rotation of the radiator elements 12.1 ... 12.5 about their axes of symmetry above a conductive base plane 17. Rotation control means 18.1 ... 18.5 for controlling the radiator element mounting structures 16.1 ... 16.5 are also provided.

The radiator elements 12.1 .. . 12.5 can individually be rotated on their mounting means 16.1 ... 16.5. This is achieved by the control means 18.1 .. . 18.5.

The feed network is indicated by reference numeral 20, and the feed port by reference numeral 22.

Assume that the feed network 20 provides a signal of equal phase between the feed port 22 and each of the radiator mounting means 16.1 ... 16.5. In order to achieve beam steering in the direction 14.1 ... 14.5, a progressive phase shift would be have to be applied to each adjacent radiator element 12.1 ... 12.5. This is achieved by controlled progressive rotation of the individual radiator elements 12.1 ... 12.5, thereby the phase of radiation of each radiator element 12.1 ... 12.5 is shifted in relation to the amount of rotation of the other radiator elements 12.1 ... 12.5.

For example, radiator element 12.1 could be rotated by 0 degrees, radiator element 12.2 by x degrees, radiator element 12.3 by 2x degrees and so forth. The relationship between the beam direction (φ) and the required phase shift (x) in a phased array is well documented in the literature.

Any radiator element 12.1 . .. 12.5 required to be rotated by more than 180 degrees could be rotated in the opposite direction by an amount of less than 180 degrees and thereby achieve the same result. N times 360 degrees can also be subtracted from any required angle larger than N times 360 degrees (N = 1, 2, . . .) In Figures 2 to 4 one example of a radiator element 12.1 is shown.

The radiator element 12.1 includes a cylindrical foam body 24 around which a helically wound conductor strip 26 and on which a coupled disc radiator 27 (see Figure 3) is provided.

By means of the arrangement in accordance with the invention, as a result of the rotation of the radiator element 12.1 about its axis of symmetry, a phase shift is provided mechanically relative to an unrotated or differently rotated radiator element.

The coupled disc radiator 27 can either be rotated with radiator element 12.1 or remain stationary without influencing the phase shift.

The phase shift achieved by the present invention can be constructed to have all the simultaneous advantages of low cost, low loss, high power handling capabilities, and allow continuous (non-discrete) phase adjustment to any phase setting.

Furthermore, the phase shifters utilized can result in a very compact antenna construction as they have very little impact on the feed structure. The control and mechanical means of rotation may be implemented within unused volume between radiator elements and therefore may have very little impact on the total array thickness.

The compactness and potential low relative cost of the phase shifters allows small inter-element spacing. This feature, together with the unlimited amount of ' phase shifter control allowed by this invention, may also allow the array to be used in an endfire mode. The choice of a radiator element with suitable low elevation coverage may then allow extremely good low elevation coverage when compared to planar phase steered arrays using larger element spacing or larger apertures to achieve the required low elevation directivity and coverage. The axis of rotation of the radiator element 12.1 is indicated by reference numeral 28.

In Figure 4 the connector 30 between the helix conductor strip 26 and the radiator element 12.1 and the feed network 20 is shown. This connector 30 may serve as a rotary joint or be connected to a rotary joint.

Figure 5 shows a rotated radiator element 12.1 and Figure 6 an unrotated radiator element 12.1 having respectively output signals "a" and "b". The output signal a has an x degree phase difference relative to signal "b".

In one embodiment the antenna 10 can be adapted as an aircraft antenna.

In Figures 7 to 9 an alternative embodiment of a radiator element is shown.

The illustrated radiator element 32 includes a housing 34 having a conductive base 36 and circumferential side wall 38. Inside the housing 34 there is provided a composite disc 40, including a conductive ground plane disc 42 on which a micro strip feed network circuit 44 is located on a substrate 45, and below it a bottom insulating sheet 46.

On top of the composite disc 40 a lower radiator metal disc 48 is provided, which disc 48 is in contact by way of feed pins 50, 52 to the radiator feed network circuit 44.

The housing 34 is closed off by means of an upper metallic cross-slot radiator disc 54 in which slots 55 are provided.

A rotary joint 56, having an inner conductor 58 and an outer conductor 60, is provided. The inner conductor 58 is connected at one end to the feed network circuit 44 of the radiator element 32 and at its Opposite end to the feed network

20 (see Figure 1). The outer conductor 60 is connected at one end to the conductive ground plane disc 42 and at its opposite end to the conductive base plane 17 (see Figure 1).

An electric drive motor 62 is located at the base 36 of the housing 34 and is drivingly coupled to the disc 42. The driving coupling can be by way of a suitable gear mesh drive.

In use, the radiator micro strip network circuit 44 is caused to excite the lower radiator disc 48 in such a way as to produce a circularly polarized mode and in turn the cross-slot radiator 54 is excited.

By operation of the motor 62 the disc 42 is rotated, and therewith the composite disc 40 and the radiator disc 48 are also rotated relative to the conductive base plane 17, and consequently the phase of the radiator element 32 is changed relative to other radiator elements, whose composite discs 40 are unrotated or are rotated differently.

Claims

PATENT CLAIMS

1. An antenna capable of creating a steerable circularly polarized directive beam, which includes

b) a conductive base plane; and

c) mounting means for each radiator element relative to the base plane.

2. An antenna as claimed in claim 1, which includes moving means adapted to rotate at least part of the radiator elements independently and angularly to obtain a phase shift relative to an unrotated radiator element or a differently rotated radiator element, and the mounting means being adapted to allow independent rotation of each radiation element relative to the base plane.

3. A phased array antenna, which includes

a) a plurality of radiator elements adapted to receive and transmit electro-magnetic wave signals, each radiator element being circularly polarized;

b) a conductive base plane;

c) mounting means for each radiator element mounting it swivelably and/or rotatably relative to the base plane;

d) a feed structure adapted to transmit signals from and to the radiator elements and combining the signals to enable connection of the radiator elements to at least one coaxial connector;

e) a plurality of rotating means adapted to independently rotate or swivel the radiator elements relative to the base plane, . thereby varying the phase shift of the signal associated with each radiator element relative to another unrotated or differently rotated radiator element; and

4. An antenna as claimed in any one of the preceding claims, in which the mounting means includes a rotary joint.

5. An antenna as claimed in claim 4, in which the rotary joint is adapted to make use of slip joints or non-ohmic capacitive coupling to achieve a low loss transmission means for the signal to or from a radiator element.

6. An antenna as claimed in any one of the preceding claims, which is of modular construction.

7. An antenna as claimed in any one of the preceding claims, in which the base plane has a planar structure.

8. An antenna as claimed in any one of claims 1 to 6, in which the base plane is conformal (non-planar).

9. An antenna as claimed in any one of the preceding claims, in which the base plane has a circular circumference.

10. An antenna as claimed in any one of claims 1 to 8, in which the base plane has an elliptical circumference.

11. An antenna as claimed in any one of claims 1 to 8, in which the base plane is rectangular with rounded corners.

12. An antenna as claimed in any one of claims 2 to 11, in which the feed structure is made up of signal transmission line sections designed to

5 achieve desired distribution of the signals to and from the radiator elements.

13. An antenna as claimed in claim 12, in which the line sections are microstrip, stripline or coaxial type feed structures.

14. An antenna as claimed in any one of the preceding claims, in which a 10 corporate or series feed structure, or combination thereof, is used.

15. An antenna as claimed in any one of claims 2 to 14, in which the feed structure connects all the radiator elements to a single coaxial connector for interfacing to coaxial cable or directly to associated communication equipment.

15 16. An antenna as claimed in any one of the preceding claims, in which each radiator element is a helix radiator element.

17. An antenna as claimed in any one of the preceding claims, in which the radiator element is a circularly polarized radiator element consisting of a crossed dipole radiator, a spiral radiator, a microstrip patch radiator, a 0 quadrafϊlar helix, or any other suitable radiator element.

18. An antenna as claimed in any one of the preceding claims, in which any two radiator elements are adjusted to have up 180 degrees phase difference between them.

19. An antenna as claimed in any one of claims 1 to 3, in which each radiator 5 element comprises a conductive housing in which are provided rotatably a conductive ground plane disc on which a radiator feed network circuit is provided, a lower radiator metal disc, operatively connected by way of feed pins to the feed network circuit, the housing being closed by an upper conductive radiator disc.

10 20. An antenna as claimed in claim 19, in which the upper radiator disc is a cross-slot radiator disc.

21. An antenna substantially as hereinbefore described with reference to and as illustrated in the accompanying schematic drawings.

22. A radiation element for an antenna substantially as hereinbefore described 15 with reference to and as illustrated in the accompanying schematic drawings.