GB2220303A

GB2220303A - Dual polarised phased array antenna

Info

Publication number: GB2220303A
Application number: GB8815439A
Authority: GB
Inventors: Peter John Gibson; Peter John Massey
Original assignee: Philips Electronic and Associated Industries Ltd
Current assignee: Philips Electronics UK Ltd
Priority date: 1988-06-29
Filing date: 1988-06-29
Publication date: 1990-01-04
Also published as: JPH0252508A; GB8815439D0; EP0349069A1

Description

2220303 1

DESCRIPTION

PHB33474 DUAL POLARISED PHASED ARRAY ANTENNA The invention relates to a dual polarised phased array antenna comprising two corresponding matrix arrays of antenna elements respectively providing orthogonal directions of polarisation. mounted on a support structure and energised by associated feeder means so as to form a phased antenna array of corresponding polarisation, said support structure comprising an assembly of two orthogonal sets of parallel insulating planar supports, the supports of one set intersecting and interengaging the supports of the other set to form a support structure of matrix form, the insulating planar supports of each set each being provided with a conductive surface pattern including a succession of said antenna elements distributed along a corresponding outward facing edge of the planar support. The respective orthogonal directions of polarisation are normally vertical and horizontal. Dual polarised phased array antennas of the kind specified can be employed in radar and other direction finding systems, and conventionally have the phase centres of their corresponding vertical and horizontal polarisation elements coincident with one another.

Such a dual polarised phased array antenna of the kind specified has been disclosed by L.R. Lewis. M. Fassett and J. Hunt, in a note entitled "A broadband stripline array elemenC, published in the IEWAP-S Symposium Program and Digest June 1974, Atlanta, Georgia, pages 335 to 337, which describes an antenna array the antenna elements of which comprise tapered notches. Figure la illustrates the form of dual polarised array therein disclosed and Figures 1b and lc respectively illustrate details of the vertical and horizontal insulated planar supports and the slots formed therein for the purpose of intersection and interengagement. Figure la shows a portion of the known dual polarised phased array antenna 1 described in the above reference which is said to 35 be a square steerable array consisting of 256 (16x16) antenna 2 PHB33474 elements 2. The support structure 3 of the antenna array 1 comprises an assembly of two orthogonal sets of parallel insulating planar supports 4.5. the supports of one set intersecting and interengaging the supports of the other set by means of corresponding co-acting slots 6, to form a support structure of matrix form. The horizontal and vertical supports 4,5, are each provided on both faces with a conductive surface in the form for example of copper cladding and a succession of antenna elements in the form of tapered notches are formed. for example by etching. so that they are distributed along a corresponding outward facing edge of the planar support 4,5, when assembled to form the matrix structure 3. In conventional manner. the phase centres 16 of the horizontally polarised antenna elements 2 on the parallel horizontal planar supports 4, are arranged to coincide with the phase centres 16 of the corresponding vertically polarised antenna elements 2 on the parallel vertical planar supports 5. This requires that the centre of each antenna element 2 must correspond to the centreline of a corresponding slot 6 in the respective planar support 4,5.

The tapered notch antenna arrays 2 are each fed by a triplate stripline feed 8 embedded in the dielectric forming the corresponding planar support, which traverses the slot and is effectively grounded to the surface conductor by an open circuit half wavelength extension on the far side. It will be apparent from Figures 1b and lc that the feeder coupling point for elements on the horizontal supports will be different in location and therefore in electrical characteristics than that for elements on the other support which means that, in general one of the arrays will not be operating under optimal conditions. one advantage of forming a dual polarised phased array antenna using a structure of interlocking planar supports which can for example comprise printed circuit boards employing a suitable dielectric such as glass fibre reinforced polytetrafluorethelene (PM) or a polyolefin, is ease and economy of manufacture. However a 3 PHB33474 significant further advantage of using circuit boards in a phased array would be the ease of mounting amplifying, receiving and phase changing circuitry on each board to control the passage of signals to and from the respective antenna elements carried on the board. However in the case of one set of boards, as will be apparent from Figure lc. the coincidence of the antenna elements 2 with the corresponding slot 6 will make it impossible to use the conductive cladding to carry interconnections along the boards from one antenna element to another and such interconnections would therefore have to be made external to the board adding to the expense of manufacture.

It is an object of the invention to provide an improved dual polarised phased array antenna which can be less costly to manufacture.

According to the invention there is provided a dual polarised phased array antenna of the kind referred to, characterised in that the phase centres of those antenna elements forming the matrix array relating to one polarisation direction, are offset from the phase centres of corresponding antenna elements forming the other matrix array. The respective phase centres of each of the antenna elements can be located on the corresponding planar support between successive intersections therewith of planar supports orthogonal thereto.

The antenna elements formed by the conductive surface pattern on the insulating planar supports, can each comprise a tapered slot antenna element formed by the conductive surface pattern on the associated insulating planar support. and preferably an exponential taper would be employed. It is however possible to employ other suitable printed circuit antenna elements such as a simple dipole or a Yagi array.

The insulating planar supports can be moulded from a suitable dielectric material or they can be formed from sheet dielectric material.by stamping, cutting or milling. The dielectric can be a suitable plastics material such as a polyolefin or preferably a glass fibre reinforced PTFE and the 4 PHB33474 conductive surface pattern can be formed, for example, from copper cladding on the insulating planar supports by means of any suitable printed circuit technique. Alternatively, the insulating planar supports can be formed of alumina or quartz and the conductive surface pattern can be formed on the surface thereof by a thick film.process or by vapour deposition, e.g. via a mask, of a suitable metallisation system, preferably nichrome-gold.

The invention provides an inexpensive method of assembling a dual polarised matrix array antenna from an assembly of component linear subarrays. The form of assembly ensures that the sub-arrays are located and maintained at the correct spacing from one another. The sub-arrays can be assembled and tested before inclusion in the assembled array, and the subarrays can be included or replaced in the complete array without introducing or removing any additional microwave wiring.

Where reference is made herein, explicitly or implicitly, to radiation of electromagnetic energy by an antenna, it should be understood to apply equally to the reception of electromagnetic energy thereby, since an antenna is a reciprocal device.

The invention is based on the realisation that in a dual polarised phased array antenna, the relative positioning accuracy of the beams of different polarisation is not significantly reduced when the phase centres relating to one direction of polarisation are displaced transversely relative to the phase centres relating to the other polarisation direction by a distance equal to about half the matrix element spacing, and that by such a displacement of the antenna elements and their associated feeders relative to intersections of interengaging insulating planar supports which form a corresponding matrix support structure for the antenna, it is possible to avoid undesirable restrictions and compromises in respect of circuit interconnections and feeder connections resulting from the presence of the interengagement slots located on the respective axes of some of the antenna elements when these are formed as PHB33474 printed circuit type conductive patterns on the insulating planar supports.

An embodiment of the invention will now be described by way of example, with reference to Figures 2,3 and 4 of the accompanying drawings, of which:- Figure 2 is a perspective diagram illustrating a portion of a dual polarised phased array antenna in accordance with the invention,, Figures 3a and 3b respectively illustrate diagrammatically the horizontal and vertical printed circuit boards employed to form the structure of Figure 2, and Figure 4 is a diagram illustrating one method of feeding an antenna element employed in the antenna of Figure 2.

Figure 2 illustrates diagrammatically and in perspective, a portion of a dual polarised phased array antenna in accordance with the invention in which a support structure 10 comprises an assembly of two orthogonal sets of parallel insulating planar supports, formed in the present example by horizontal and vertical dielectric plates 11. 12, respectively, the planar supports of one set intersecting and interengag"ing the planar supports of the other set so as. to provide the support structure 10 of matrix form. This interengagement is effected by providing each of the planar supports 11,12, at the respective points of intersection with the planar supports 12..11, of the other set, with a cooperating discontinuity in the form of a slot 14 formed, in the present example, to half way across the support from front to back.

Each of the insulating planar supports 11,12, of each set is provided with a patterned conductive surface layer 15 which includes a succession of antenna elements 17 distributed along a corresponding outward facing edge of the planar support 11,12, which faces in the general direction to which or from which electromagnetic radiation is to be projected or received by the antenna structure 10. In the present example each antenna element 17 is in the form of an end-fire tapered slot antenna 6 PHB33474 comprising a slot in the planar conducting surface layer 15 and each slot has an exponential taper from the throat 18 (Figure 4) to the open end 22 of the tapered slot antenna element 17. This form of antenna is sometimes called a Vivaldi antenna and is described in United Kingdom Patent Number GB 1.601.441. That description is hereby assumed to be incorporated herein and for this reason the antenna element will not be further described in detail herein. The throat or narrow end 18 of the slot is connected to an open circuit loop 19 and is connected to a feeder 20 which can be a strip line or the central conductor of a triplate line when, in the latter case, the patterned conductive surface layer 15 is repeated on the other major surface of a layered dielectric sheet 11. A connecting pillar 21 connects the end of the line 20 to the conductive surface layer 15 forming the ground plane of the feeder, on the far side of the throat 18.

The Vivaldi antenna element provides an electrical polarisation direction which is coplanar with the plane of the dielectric plate on which it is formed. Thus the parallel assembly of the vertical planar supports 12 each with a linear array of Vivaldi elements 17 forms a matrix array of antenna elements with a vertical direction of polarisation and the parallel assembly of the horizontal planar supports 11 forms a corresponding matrix array of antenna elements with a horizontal direction of polarisation.

A conventional dual polarised phase array antenna. as illustrated for example in Figure 1, is arranged so that the phase centres of the corresponding vertically and horizontally polarised elements of the array are coincident.

In the antenna of Figure 2, however, in accordance with the invention, the phase centres 16 of those antenna elements 17 on the planar supports 11 forming the matrix array relating to one polarisation direction (horizontal), are offset from the phase centres 16 of corresponding antenna elements 17 on the planar supports 12 forming the matrix array relating to the other polarisation direction. In the embodiment shown in Figure 2, the 7 PHB33474 respective phase centre 16 of each of the antenna elements 17, is located on the corresponding planar support 11,12, between successive points of intersection therewith of planar supports 12.11. orthogonal thereto. which correspond to the locations of the slots 14. and in the present example the elements 17 are located midway between successive slots 14. This step is based on the realisation that the transverse offset displacement of the phase centres of the matrix array relating to one direction of polarisation relative to the corresponding phase centres of the matrix array relating to the other polarisation direction by a distance of about one half of the interelement spacing of either matrix.. will only affect the accuracy of coordinating and tracking the directions of the respective orthogonally polarised beams to a negligible extent. As a result of this displacement of the antenna elements from the plate intersections, the dual polarised phased antenna array can be constructed entirely from printed circuit boards which are then simply slotted together to form the matrix antenna structure 10. Each of the circuit boards 11,12, can include conventional amplifying, modulating, switching, phase shifting and timing means (not shown) associated with the individual antenna elements 17 of the linear array formed thereby in order to perform the function of a phased array. External electrical connections can readily be provided to each board 11,12, via printed circuit cable connectors attached to the rear edge of the board, and connected to conventional circuitry for further phasing the corresponding parallel assembled linear arrays forming the associated matrix for reception and/or transmission of signals in three dimensions and having the corresponding polarisation direction. The plates 11 and 12 can be formed from conventional microstrip or triplate boards.

The plates 11,12, can be moulded or they can be formed from sheet dielectric material by stamping, cutting or milling. A suitable sheet dielectric is glass fibre reinforced PTFE. The conductive surface pattern can be formed by a printed circuit 8 PHB33474 technique from copper cladding applied to the surface of the plates 11,12. Another suitable dielectric is alumina and the conductive surface pattern can be formed by a thick film technique or by vapour deposition of nichrome-gold or aluminium via a mask. Other suitable dielectric support materials are quartz, titanium dioxide, gallium arsenide or high- purity silicon.

Although Figure 2 shows only part of the antenna array embodying the invention, the remainder of the antenna will be substantially identical in construction to that shown in Figure 2, and in one example each component polarised array comprised a matrix of 8 x 8 antenna elements. In practice, a dual polarised phased array antenna having a larger number of antenna elements can readily be constructed in accordance with the invention.

The invention is not limited to the use of tapered slot antenna elements, and if elements having a wider beamwidth were required, tapered notch elements similar to those described in the previously mentioned paper by Lewis et at., can be employed. The advantages of the invention can also be realised when employing other forms of end-fire printed circuit antenna elements such as a dipole element or an end-fire array of dipole elements, for example a Yagi array.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the design, manufacture and use of dual polarised phased array antennas and component parts thereof and which may be used instead of or in addition to features already described herein. Although claims have been formulated in this application to particular combinations of features. it should be understood that the scope of the disclosure of the present application also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it 9 PHB33474 mitigates any or aLL of the same technicaL probLems as does the present invention. The appLicants hereby give notice that new cLaims may be formuLated to such features and/or combinations of such features during the prosecution of the present appLication or of any further appLication derived therefrom.

PHB33474

Claims

CLAIM (S)

1. A dual polarised phased array antenna comprising two corresponding matrix arrays of antenna elements respectively providing orthogonal directions of polarisationo mounted on a support structure and energised by associated feeder means so as to form a phased antenna array of corresponding polarisation, said support structure comprising an assembly of two orthogonal sets of parallel insulating planar supports, the supports of one set intersecting and interengaging the supports of the other set to form a support structure of matrix form. the insulating planar supports of each set each being provided with a conductive surface pattern including a succession of said antenna elements distributed along a corresponding outward facing edge of the planar support. characterised in that the phase centres of those antenna elements forming the matrix array relating to one polarisation direction, are offset from the phase centres of corresponding antenna elements forming the other matrix array.

2. An antenna as claimed in Claim 1.. characterised in that the respective phase centre of each of said antenna elements is located on the corresponding planar support between successive intersections therewith of planar supports orthogonal thereto.

3. An antenna as claimed in Claim 1 or Claim 2, characterised in that each said antenna element comprises a tapered slot antenna element formed on the associated insulating planar support.

4. An antenna as claimed in Claim 3, characterised in that the respective longitudinal slot forming each tapered slot antenna element is provided with a substantially exponential taper.

5. An antenna as claimed in any one of the preceding claims.. characterised in that the insulating planar supports are formed from sheet dielectric.

6. An antenna as claimed in any one of the preceding claims, characterised in that the insulating planar supports are formed from a polyolefin.

11 PHS33474

7. An antenna as claimed in any one of Claims 1 to 5, characterised in that said sheet dielectric is glass fibre reinforced PTFE.

8. An antenna as claimed in any one of the preceding claims,, characterised in that the conductive surface pattern is formed from copper cladding applied to the insulating planar supports, by means of a printed circuit technique.

9. An antenna as claimed in any one of Claims 1 to 4, characterised in that the insulating planar supports are formed of alumina.

10. An antenna as claimed in any one of Claims 1 to 4, characterised in that the insulating planar supports are formed of quartz.

11. An antenna as claimed in any one of the preceding claims, characterised in that the conductive surface pattern is formed by a thick film process.

12. An antenna as claimed in Claim 9 or Claim 10, characterised in that the conductive surface pattern is formed by vapour deposition.

13. A dual polarised phased array antenna, substantially as herein described with reference to Figures 2,3 and 4 of the accompanying drawings.

Published 1989 atThe patent Office, State House, 66/171 HighHolborn, London WCIR4TP. Further copies maybe obtained from The PatentOffice. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Com 1/87