Procédés et dispositifs de couplage de signaux

Abstract

 Signal coupling arrangements are described in which the effect of unwanted signals transferred between two antennas is compensated for. In one arrangement a microstrip edge coupler is used as a compensation network to provide a cross-coupling path for the transfer of a compensating signal between two antenna signal paths. In another arrangement, an antenna assembly includes cross-slots which, in association with a conductive ring, provide two mutually orthogonally polarised radiation signals and connections to the conductive ring have closely spaced portions which provide compensation for and minimise the effect of unwanted mutual coupling.

Description

[0001] This invention relates to signal coupling methods and arrangements which are particularly, though not exclusively, applicable to the coupling of signals to and from antennas.

[0002] One arrangement to be described below, by way of example in illustration of the invention, is directed to the provision of a coupling which has a comparatively small profile, and which operates with a comparatively wide bandwidth with good performance, including at microwave frequencies.

[0003] A feature of this arrangement is that it has a printed ring shaped conductor which is coupled to two signal ports at points which are approximately 90 apart on the conductor ring. The ring conductor is coupled to a printed cross-slot conductor pattern which, during operation develops across the respective slots, two electromagnetic fields at two mutually orthogonal polarisations. The use of a cross-slot pattern to match a patch antenna has previously been proposed, for instance by Edimo et al in Electronics Letters, 10 September 1992, Vol. 28, No. 19, but there was no suggestion that a circular ring-shaped or other shaped loop conductor should be used to provide the coupling with the cross slots. Since the two signal input ports excite orthogonal radiation modes, there is little or negligible interaction between them.

[0004] In particular arrangements to be described below, by way of example, in illustration of the invention, crossed slot fields excite 'fringing' electromagnetic fields around the edge of a metal patch, from which when the antenna is transmitting they radiate as two separate, but substantially coincident, conically shaped propagation patterns. The patch is not essential to the operation of the embodiments, but it results in the provision of more concentrated beams, i. e. beams having a narrower angle of propagation than they would otherwise have. Other parasitic elements may be used to provide other shapes of propagation pattern. On the other hand it is possible to employ embodiments having no parasitic element, such as a patch.

[0005] It is also possible to employ a reflector plate in order to confine the beams to one general direction of propagation. On the other hand, should propagation in two opposite directions be required, or not be objectionable, it is possible to omit a reflector plate.

[0006] Arrangements illustrative of the one arrangement described above and illustrative of the invention will now be described, by way of example, with reference to Figs. 1 to 4 of the accompanying drawings in which:

• Figs. 1 and 2 show respectively diagrammatic plan and side views of components of a first antenna, and
• Figs. 3 and 4 show respectively diagrammatic plan and side views of components of a second antenna.

[0007] Referring to Figs. 1 and 2, there are shown a square metal patch radiating element 51 and a reflector plate 55.

[0008] Between the patch element 51 and the reflector plate 55 there is a printed circuit board (pcb) 52. On one side of the printed circuit board 52, there is a metallised pattern in the shape of a ring 58 from which there extend two legs 59 which terminate in respective ports 57a and 57b at an edge of the board 52.

[0009] The legs 59 provide a coupling for signals passing to and from the ring 58 and the ports 57a and 57b, and the legs 59 are connected to the ring 58 at points which are nominally physically 90 apart around the ring 58. The nominal 90 spacing between the points of connection of the legs 59 to the ring 58 is related to the frequency at which the antenna is intended to operate. Having regard to the dielectric material of the printed circuit board 52, the nominal length of the loop of the ring is designed to constitute one wavelength of the operating frequency of the antenna. With this arrangement, any coupling between the connection points on the ring 58 to the legs 59, and thus between the ports 57a and 57b, is minimised because the two signal paths in opposite directions around the ring between the connection points effectively differ by one half a wavelength of the signal, and signals reaching each of the respective connection points after travelling in the opposite directions will be of equal and opposite polarity.

[0010] Although in the particular arrangement being described, where the preferred transmitting or receiving radiation pattern associated with the antenna is along an axis perpendicular to the plane of the ring, the length of the ring 58 is nominally equal to one wavelength of the signal, it is possible where, for example, other radiation patterns are required for the circular length of the ring 58 to be a multiple of the nominal signal wavelength. It is also possible for the ring 58 to be of some other shape than circular, for example, it may be square, or oval, or even follow an irregular shape, according to the antenna sensitivity or the radiation pattern required.

[0011] On the other side of the printed circuit board 52 from the ring 58, there is a conductive sheet having two slots 54a and 54b therein. The slots 54a and 54b cross one another at 90 , and have a common centre which is aligned with the centre of the ring 58. One arm of the slot 54a coincides with a point on the ring 58 which is angularly mid-way between the connection points on the ring 58 of the legs 59.

[0012] The connections between the ring 58 and the ports 57a and 57b are thus at points on the ring 58 which are respectively nominally spaced from the apparent point of coincidence of the one arm of the slot 54a with the ring 58 by angles of 45 .

[0013] The slots 54a and 54b, which are each nominally one half wavelength in length at the operating frequency in the embodiment being described, extend to points which are beyond and outside the projection on them of the ring 58. As a result, two fields of resonance, which are exited in the slots 54a and 54b, together with the fields associated with the ring conductor 58 create a pattern of sensitivity or radiation which extends in a cone shape outwardly around the edges of the patch 51, where such a patch is provided.

[0014] On the other side of the printed circuit board 52 from the radiating plate 51, there is a reflector plate 55 which extends beyond the projections of the other components of the antenna. Although the use of such a reflector is preferred in the embodiment being described, it is not essential. The reflector 55 need not be flat, it may have upstanding side walls, or be dish shaped. Its effect is either to make the antenna more sensitive to radiations received by the antenna components 51 and 52, or to restrict the emission of radiations from these components to directions away from the reflector.

[0015] Advantages of the structure which has been described with reference to Figs. 1 and 2 are that it is capable of operation over a wide bandwidth, is compact, and has a comparatively small edge to edge dimension so that it has a relatively small profile when in use.

[0016] Since the excitation of the antenna described above is symmetrical, the resulting patterns for the two orthogonal polarisations will be nominally identical giving good tracking between the signals from the two ports 57a, 57b. Previous proposals having similar objects, such as those featured in the specification of the European patent application published under number 605338 on July 6 1994, do not have this feature of symmetry, so that the patterns are not similar, and the antenna pattern tracking is inferior.

[0017] The particular arrangement described above utilizes only one substrate layer for the connections to the feed ports 57a, 57b, which simplifies the production of the antenna, as well as simplifying the electrical symmetry. The proposed construction discussed in the Electronics Letters reference mentioned above employed an insulating layer to separate two orthogonal microstrip lines, which would make the volume manufacture of the antenna proposed in that publication more difficult.

[0018] Referring to Figs. 3 and 4, there is shown a slightly different conductor track geometry, which follows a symmetrical pattern. The arrangements of ports 57c and 57d are on opposite edges of the printed circuit board 52 and are connected to the ring 58 via an edge coupled microstrip, indicated at 59a by closely spaced lengths of the two legs 59, so arranged that residual mutual coupling, particularly between the antenna ports 57c and 57d, can be minimised.

[0019] The dielectric between the elements of the antenna may be other than the material of the printed circuit board 52, for example, it may be air, and the ring 58 may be spaced from the slots 54a and 54b in some other way. It will be appreciated that the dimensions of the components of the antenna will depend not only upon the frequency of operation but also upon the characteristics of the components, including that of the dielectric.

[0020] In summary, there have been described above antenna arrangements which operate at two mutually orthogonal polarisations, and which have two input ports, respective feed paths from the ports to two spaced points on a conductive ring, a pair of cross slots in a conductive sheet located in a plane spaced from that of the conductive ring and centralized with respect to it, such that two coincident radiation paths at crossed polarisations are created generally along an axis perpendicular to the plane of the ring, in one or both directions, and wherein the spaced points on the ring, the ring itself and the slots are so located and dimensioned, that a higher degree of isolation is achieved between the two radiation signals of orthogonal polarisation, than the isolation provided by virtue of their orthogonal polarisation alone. There may be a patch plate or other parasitic radiating element arranged about the axis which is normal to the plane of the ring. The spaced points on the ring 58 may each be at a respective point which is nominally 45° around the ring in a direction opposite to that of the other relative to one of the two slots, according to the frequency of operation, and having regard to the particular dielectric employed. The circumference of the ring 58 in the examples is nominally one wavelength of the operating frequency.

[0021] The slots 54a, 54b are nominally one half wavelength in length at the operating frequency and they cross at their mid points perpendicularly to each other. Other slot geometries are possible. For example, each main slot may have a slot at each of its ends which is perpendicular to the main slot, thereby forming t- junctions at the ends of the main slot. The conductive ring 58 and/or the slots 54a, 54b may be applied to opposite surfaces of the printed circuit board 52. A conductive rear reflector or reflecting cavity 55 may be located on the opposite side of the printed circuit board 52 from a patch plate 51. The cross slots 54a, 54b may be voids in a conductive sheet printed on the surface of the printed circuit board 52 facing the rear reflector 55, or on the surface remote from the reflector.

[0022] An edge coupler may be provided over chosen lengths of the feed paths or legs 59, to couple between microstrip feed paths 59a for improved isolation.

[0023] It will be understood that although particular arrangements, illustrative of the invention have been described, by way of example, variations and modifications thereof, as well as other arrangements employing the invention may be made.

[0024] For example, the ring 58 which has been described has a physical length of either one wavelength or a multiple thereof at the operating frequency, and feed connections, are provided which are separated by 90 in one direction and 270 in the other direction around the ring, in order to provide signals at the connection points which cancel or are at null points. It will be understood that by making the ring 58 of a different relative length compared to the operating frequency, feed points may be chosen at different angular positions than those described in order to provide a similar effect.

[0025] For example the length of the ring 58 may be λ/2.

[0026] It has been explained that the geometry of the ring 58 may be other than circular, for example square, or oval, or even have an irregular meandering shape. It is also possible for the ring 58 not to be physically continuous. For example, there may be a physical interruption in the length of the ring 58 which introduces a desired electrical, for example, capacitive characteristic, though it is electrically continuous.

Claims

1. A signal coupling arrangement including antennas which operate at two mutually orthogonal polarisations, two input ports, feed means from the ports to two spaced points on a conductive ring, a conductive sheet having a pair of cross slots therein in a plane spaced from that of the conductive ring and centralized with respect to it, for providing two radiation paths at crossed polarisations substantially perpendicular to the plane of the ring, the spaced points on the ring, the ring, and the slots being so arranged that a higher degree of isolation between two radiation signals of orthogonal polarisation may be obtained than the degree of isolation provided by virtue of the orthogonal polarisation of the radiation signals alone.

2. A signal coupling arrangement as claimed in claim 1 in which the spaced points on the ring are each at a point which is substantially 45 around the ring in opposite directions from one another from a point at which a slot overlaps the ring.

3. A signal coupling arrangement as claimed in claim 2 in which the ring is circular and has a circumference which is substantially one wave wavelength of the operating frequency of the antennas.

4. A signal coupling arrangement as claimed in claim 1 including a parasitic radiating element in a plane parallel to and on one side of the conductive ring and conductive sheet and a reflector in a plane parallel to and on the other side of the conductive ring and conductive element from the parasitic radiating element.

5. A signal coupling arrangement as claimed in claim 1 in which the respective connection means from the ports include legs having closely spaced portions this arrangement being positioned at a distance from the ring connection points in order to provide a cancellation signal for minimizing the effect of unwanted mutual coupling

6. A signal coupling arrangement as claimed in claim 1 in which the conductive ring is electrically and physically continuous.

Dessins