Dual polarisation antennas

Description

[0001] This invention relates to dual polarisation antennas.

[0002] Today, increasingly many wireless telecommunication systems employ a polarisation diversity scheme to overcome the undesirable effect of multipath fading which is caused by multiple reflection of radio signals in a mobile radio environment. Multipath fading introduces unpredictable changes to the phase and polarisation characteristics of the signals and often results in an amplification, or in some cases a cancellation, of signals at specific locations. This random and large fluctuation of signal strength caused by multipath fading can therefore severely affect system performance and reliability, and in extreme cases leads to momentary loss of communication between mobile units and base stations.

[0003] In a polarisation diversity system, the uncorrelated radio paths are provided by two orthogonal polarisations, which are commonly either polarisations in vertical and horizontal planes or in slant planes at +45° and -45°. One of the main advantages of employing polarisation diversity is that the antenna elements needed to provide the two polarisations can be physically integrated and manufactured as a single antenna unit. This type of antenna is commonly referred to as a dual polarisation antenna.

[0004] A dual polarisation antenna has to meet certain electrical specifications, among which the port-to-port isolation between the two polarisations is of particular importance to system operators due to the advantage of lowering the performance required on other expensive system components in a base station.

[0005] Published PCT patent specification No. WO99/05754 shows various dual polarisation antenna arrays in which port-to-port isolation is improved using parasitic elements which surround or flank the antenna elements, which are laterally spaced from the antenna elements and which have an open frame-like structure, and discloses the preamble of independent claim 1.

[0006] Many dual polarisation antennas are designed using microstrip transmission lines to form the feed/reception network, which carries signals of the two polarisations to and from the radiating elements in the antenna. The radiating elements that are capable of radiating and receiving dual polarisation signals are designed with patch technology due to the associated lower manufacturing cost and the desirable slim profile of the antenna. These radiating patches are associated with the feed/reception channels using aperture coupling techniques or other forms of coupling.

[0007] According to the invention there is provided an antenna for transmission/reception of dual polarised radio signals, the antenna comprising feed lines, a radiating patch, a panel and a parasitic element, wherein said feed lines feed rf signals to and from said radiating patch, said radiating patch being of square or circular shape, and said patch mounted parallel to said panel, wherein said panel, or a conductive surface thereon, acts as ground plane, and wherein said parasitic element acts as a radiating element for cancelling unwanted cross-couplings by radiation in the vicinity of the patch, characterised in that the parasitic element is disposed in the volume between said radiating patch.

[0008] Preferably, the patch and the parasitic element are defined by metal areas formed on mutually opposite surfaces of a patch panel which is conveniently mounted on the support panel in spaced parallel relationship therewith.

[0009] The metal area defining the parasitic element is preferably in the shape of an elongated strip, conveniently a curved strip. In a preferred embodiment the parasitic element is a part-circular metal strip, subtending an angle of about 270° symmetrically disposed with relation to the radiating patch.

[0010] The metal area of the patch is preferably capacitively coupled, by uncoated metal areas, to two metal coated areas aligned along orthogonal axes for handling the orthogonally polarised radio signals, the two metal coated areas forming part of the feed/reception means.

[0011] The radiating patch and the parasitic element may form a patch assembly and the antenna may have a plurality of such patch assemblies, in which case the feed/reception means preferably take the form of a feed/reception network in the form of conductive tracks formed by conductive metal areas deposited on the support panel.

[0012] The provision of the parasitic element achieves high port-to-port isolation of a dual polarisation antenna.

[0013] A preferred antenna comprises an array of four separated radiating and receiving patch assemblies, which are capable of handling two independent and orthogonally polarised signals simultaneously. There are two input ports for each patch assembly and the ports that correspond to the two polarisations are capacitively coupled to the corresponding tracks of the feed/reception network. The parasitic elements, which form part of the patch assemblies, provide a mechanism which effectively reduces the undesirable cross-polarisation couplings created by radiation in the vicinity of the patch assemblies.

[0014] An antenna according to the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is an isometric view of the antenna,

Figure 2 shows the antenna with its main components in exploded view but with certain detail omitted for clarity,

Figure 3 is a view of the lower panel and upper panel of a patch assembly of the antenna of Figures 2, and

Figure 4 shows a detail of one patch assembly of the antenna.

Figure 5 is a plan view of the antenna, looking in the direction of arrow II in Figure 2 but with certain detail omitted for clarity, and

Figure 6 illustrates, in exploded view, the parts of a simplified antenna, also in accordance with the invention.

[0015] The antenna shown in the drawing is a wide-band low profile dual polarisation antenna capable of receiving and transmitting (either sequentially or simultaneously), orthogonally polarised radio signals. The antenna comprises an array of four patch assemblies 1, 2, 3, 4 and an elongated, grounded panel 5. Panel 5 and patch assemblies 1, 2, 3, 4 are dielectric materials clad with copper in pre-determined patterns on one or both surfaces, preferably by an etching process. Panel 5 and the four patch assemblies 1, 2, 3, 4 are mounted on an elongated supporting base panel 6 of aluminium.

[0016] The patch assemblies 1, 2, 3 and 4 are identical in this case and each comprises a stack of two circular panels. Alternatively, the panels could be either square or a combination of circular and square. The lower circular panel 11 is held in spaced parallel relationship with respect to the panel 5 next beneath it by means of an insulating spacer. The lower surface of the lower circular panel 11 has a parasitic radiating element 12 formed by a copper track deposited on the lower surface of the panel 11. The upper surface of the lower circular panel 11 is coated with copper in a circular shape except for two arc-shaped slots 13, 14. The two slots 13, 14 are uncovered areas on the otherwise copper coated surface, which separate the two copper areas 15, 16 defined by the two slots 13, 14 from the remaining area 17 of the copper coating. The two slots 13, 14 are located near the edge of the circular panel and are disposed symmetrically at 45° with respect to the axis of symmetry which passes centrally between the two areas 15 and 16. The parasitic element 12 is also symmetrical with respect to this axis, subtending an angle of 135° on each side of the axis. Moreover, the element 12 is disposed wholly within the volume defined between the coating area 17 and the panel 6. In this case, the element 12 is wholly within the volume defined between the coating area 17 and the panel 5, and lies within the plan area or "footprint" of the area 17.

[0017] The upper circular panel 18 of each patch assembly is held in spaced parallel relationship with respect to the lower circular panel 11 next beneath it by means of an insulating spacer. The upper circular panel 18 is made of dielectric material with a circular pattern of copper coating 19 on the lower surface of the panel. This upper circular panel could be made of a solid metal, such as aluminium.

[0018] It will be appreciated that both the surface 19 and the area 17 act as radiating patches.

[0019] The upper surface of the panel 5 is copper coated while the lower surface has a feed/reception network comprising two channels 20 and 21 each terminating in a respective terminal 22 or 23. The channels 20 and 21 are essentially mirror images of each other and are formed by copper tracks deposited on the lower surface of the panel 5. Each channel divides into four separate feed lines 20a, 20b, 20c, 20d and 21a, 21b, 21c, 21d respectively. Each feed line terminates in an open circuit whereby a small metal pin 24 is used to connect the corresponding feed line, through the panel 5, to the lower circular panel of a patch assembly. The patch assemblies 1, 2, 3, 4 and panel 5 are supported on the support base panel 6 by means of spacer 25 (Figure 4).

[0020] In use as a transmitting antenna, input signals are applied to the terminals 22 and 23, with signals polarised in one plane being applied to the terminal 22 and signals polarised in the orthogonal plane being applied to the terminal 23. The input signals are conducted along the feed channels 20 and 21 to the feed lines 20a, 20b, 20c, 20d and 21a, 21b, 21c, 21d respectively. At the open end of each feed line, the conductive pin 24 conducts the signals from the corresponding feed line to the area 15 or 16. By means of capacitive coupling through the slots 13, 14, signals are coupled to the area 17 of the copper coating on the upper surface of the lower circular panel. The position (i.e. distance from the edge) and dimension (i.e. arc length) of the two slots 13, 14 are selected for best impedance matching. The relative permittivity, thickness and, dimensions of the lower panel and the upper circular panel of the patch assembly are selected for optimal broadband impedance matching, the upper circular panelling electro magnetically coupled to the area 17.

[0021] Unwanted cross-couplings created by radiation from within the patch assemblies 1, 2, 3, 4 are significantly reduced by the parasitic elements 12 formed on the lower surfaces of the lower circular panels. Each parasitic element 12 acts as a radiating element which radiates energy of the two polarisations into the vicinity of the patch assembly. This radiation, when adjusted properly, can actively cancel the unwanted cross-coupling radiation in the region, which results in high isolation between the polarisations. The position, shape, length and width of each parasitic element are selected for optimal isolation at the frequencies of interest.

[0022] Figure 6 illustrates a simplified antenna having only one patch assembly which in structure corresponds to one of the patch assemblies 1 to 4 of Figures 1 to 4. The antenna of Figure 6 is devoid of the panel 5 and the feed/reception tracks, signals being conducted to the respective areas 15, 16 by conductive cables rods or pins 26. As before, the areas 15, 16 are capacitively coupled to the main conductive area 17 on the upper surface of the lower panel 11, the lower surface of which has an arcuate parasitic element 12 subtending an angle of about 270° symmetrically arranged with respect to the areas 15 and 16. The parasitic element 12 lies wholly within the volume defined between the coating area 17 and the 6, and within the plan area or "footprint" of the coating area 17.

Claims

1. An antenna for transmission/reception of dual polarised radio signals, the antenna comprising feed lines (20-23, 15, 16)) a radiating patch (17), a panel (5, 6), and a parasitic element (12), wherein said feed lines (20-23, 15, 16) feed rf signals to and from said radiating patch (17), said radiating patch being of square or circular shape, and said patch mounted parallel to said panel (5, 6), wherein said panel (5, 6), or a conductive surface thereon, acts as ground plane, and wherein said parasitic element (12) acts as a radiating element for cancelling unwanted cross-couplings by radiation in the vicinity of the patch (17) characterised in that the parasitic element is disposed in the volume between said radiating patch (17) and said panel (5, 6)

2. An antenna according to claim 1 in which the panel (5, 6) comprises a support panel on which the radiating patch (17) is mounted.

3. An antenna according to either of the preceding claims, in which the radiating patch is either one of a first radiating patch (17) situated immediately adjacent the first panel and a second radiating patch (19) which is mounted adjacent the first patch (17) so that the first patch (17) is interposed between the second patch and the panel; the first radiating patch (17) being capacitatively coupled to the feed/reception means, the second patch (19) being electromagnetically coupled to the first patch.

4. An antenna according to any of claims 1 to 3, wherein the patch (17) and the parasitic element (12) are defined by metal areas formed on mutually opposite surfaces of a patch panel (11).

5. An antenna according to claim 4 when appended to claim 2, wherein the patch panel (11) is mounted on the support panel (6) in spaced parallel relationship therewith.

6. An antenna according to claim 4 or 5, wherein the metal area defining the parasitic element (12) is in the shape of an elongated strip.

7. An antenna according to claim 6, wherein the elongated strip (12) is a curved strip.

8. An antenna according to any of claims 4 to 7, wherein a metal area (17) defining the patch is capacitively coupled, by uncoated areas (13, 14), to two metal coated areas (15, 16) aligned along orthogonal axes, the areas being operable to handle the orthogonally polarised radio signals, the two metal coated areas forming part of the feed/reception means (20, 21, 22, 23, 15, 16).

9. An antenna according to claim 8, when appended to claim 7, wherein the parasitic element (12) is an arcuate metal strip, subtending an angle of about 270° symmetrically disposed with relation to an axis of symmetry of the radiating patch, which axis passes centrally between said metal coated areas (15, 16) which form part of the feed/reception means (20, 21, 22, 23, 15, 16).

10. An antenna according to any of the preceding claims, wherein the radiating patch (17) and the parasitic element (12) form a patch assembly (1) and the antenna has a plurality of such patch assemblies (1, 2, 3, 4).

11. An antenna according to claim 10, wherein the feed/reception means take the form of a feed/reception network having conductive tracks (20, 21, 22, 23) formed by conductive metal areas deposited on the panel.

12. An antenna according to claim 11 and comprising an array of four separated radiating and receiving patch assemblies (1, 2, 3, 4), which are capable of handling two independent and orthogonally polarised signals simultaneously, there being two input ports (15, 16) for each patch assembly and the ports that correspond to the two polarisations capacitively coupling the patch assemblies to the corresponding tracks (20, 21, 22, 23) of the feed/reception network.

13. An antenna according to any of the preceding claims, in which the parasitic element (12) is interposed between the radiating patch and the panel.

Ansprüche

1. Antenne für die Übertragung/den Empfang von doppelt-polarisierten Funksignalen, wobei die Antenne Speiseleitungen (20-23, 15, 16), ein abstrahlendes Feld (17), eine Tafel (5, 6) und ein parasitäres Element (12) umfaßt, wobei die Speiseleitungen (20-23, 15, 16) HF-Signale zu dem abstrahlenden Feld (17) hin speisen und von diesem weg, wobei das abstrahlende Feld von quadratischer oder kreisförmiger Gestalt ist und das Feld parallel zu der Tafel (5, 6) befestigt ist, wobei die Tafel (5, 6) oder eine leitende Oberfläche darauf als eine Masseebene wirkt und wobei das parasitäre Element (12) als ein abstrahlendes Element zum Aufheben unerwünschter Kreuzkopplungen durch Strahlung in der Nähe des Felds (17) wirkt, dadurch gekennzeichnet, daß das parasitäre Element in dem Volumen zwischen dem abstrahlenden Feld (17) und der Tafel (5, 6) angeordnet ist.

2. Antenne nach Anspruch 1, bei der die Tafel (5, 6) eine Stütztafel umfaßt, auf der das abstrahlende Feld (17) angebracht ist.

3. Antenne nach einem der vorhergehenden Ansprüche, bei der das abstrahlende Feld ein erstes abstrahlendes Feld (17) unmittelbar neben der ersten Tafel oder ein zweites abstrahlendes Feld (19) ist, das neben dem ersten Feld (17) angebracht ist, so daß das erste Feld (17) zwischen dem zweiten Feld und der Tafel angeordnet ist; wobei das erste abstrahlende Feld (17) kapazitiv an das Speise-/Empfangsmittel gekoppelt ist, wobei das zweite Feld (19) elektromagnetisch an das erste Feld gekoppelt ist.

4. Antenne nach einem der Ansprüche 1 bis 3, wobei das Feld (17) und das parasitäre Element (12) definiert sind durch auf zueinander gegenüberliegenden Oberflächen einer Feldtafel (11) ausgebildete Metallbereiche.

5. Antenne nach Anspruch 4, bei Anhang an Anspruch 2, wobei die Feldtafel (11) auf der Stütztafel (6) in einer beabstandeten parallelen Beziehung dazu angebracht ist.

6. Antenne nach Anspruch 4 oder 5, wobei der das parasitäre Element (12) definierende Metallbereich in Gestalt eines länglichen Streifens vorliegt.

7. Antenne nach Anspruch 6, wobei der längliche Streifen (12) ein gekrümmter Streifen ist.

8. Antenne nach einem der Ansprüche 4 bis 7, wobei ein das Feld definierender Metallbereich (17) durch unbeschichtete Bereiche (13, 14) kapazitiv an zwei metallbeschichtete Bereiche (15, 16) gekoppelt ist, die entlang orthogonaler Achsen ausgerichtet sind, wobei die Bereiche dahingehend betätigt werden können, die orthogonal polarisierten Funksignale zu verarbeiten, wobei die zwei metallbeschichteten Bereiche Teil der Speise-/Empfangsmittel (20, 21, 22, 23, 15, 16) bilden.

9. Antenne nach Anspruch 8, bei Anhang an Anspruch 7, wobei das parasitäre Element (12) ein gekrümmter Metallstreifen ist, der einem Winkel von etwa 270°, symmetrisch angeordnet in Bezug auf eine Symmetrieachse des abstrahlenden Felds, die Zentral zwischen den metallbeschichteten Bereichen (15, 16) hindurchläuft, gegenüberliegt, wobei die metallbeschichteten Bereiche Teil der Speise-/Empfangsmittel (20, 21, 22, 23, 15, 16) bilden.

10. Antenne nach einem der vorhergehenden Ansprüche, wobei das abstrahlende Feld (17) und das parasitäre Element (12) eine Feldanordnung (1) bilden und die Antenne mehrere derartiger Feldanordnungen (1, 2, 3, 4) aufweist.

11. Antenne nach Anspruch 10, wobei die Speise-/Empfangsmittels die Form eines Speise-/Empfangsnetzes mit Leiterbahnen (20, 21, 22, 23) annimmt, die durch auf der Tafel abgeschiedene leitende Metallbereiche gebildet werden.

12. Antenne nach Anspruch 11 und ein Array aus vier getrennten abstrahlenden und empfangenden Feldanordnungen (1, 2, 3, 4) umfassend, die in der Lage sind, gleichzeitig zwei unabhängig und orthogonal polarisierte Signale zu verarbeiten, wobei es zwei Eingabeports (15, 16) für jede Feldanordnung gibt und die den beiden Polarisationen entsprechenden Ports die Feldanordnungen kapazitiv an die entsprechenden Bahnen (20, 21, 22, 23) des Speise-/Empfangsnetzes koppeln.

13. Antenne nach einem der vorhergehenden Ansprüche, bei der das parasitäre Element (12) zwischen dem abstrahlenden Feld und der Tafel angeordnet ist.

Revendications

1. Antenne d'émission/réception de signaux radio à double polarisation, l'antenne comprenant des lignes d'alimentation (20 à 23, 15, 16), un répartiteur rayonnant (17), un panneau (5, 6) et un élément parasite (12), dans laquelle lesdites ligne d'alimentation (20 à 23, 15, 16) alimentent des signaux rf vers et depuis ledit répartiteur rayonnant (17), ledit répartiteur rayonnant étant d'une forme carrée ou circulaire, et ledit répartiteur étant monté parallèlement audit panneau (5, 6), dans laquelle ledit panneau (5, 6), ou une surface conductrice sur celui-ci, sert de plan de masse, et dans lequel ledit élément parasite (12) sert d'élément rayonnant pour supprimer des couplages réciproques indésirables par rayonnement au voisinage du répartiteur (17) caractérisée en ce que l'élément parasite est disposé dans le volume entre ledit répartiteur rayonnant (17) et ledit panneau (5, 6).

2. Antenne selon la revendication 1, dans laquelle le panneau (5, 6) comprend un panneau de support sur lequel est monté le répartiteur rayonnant (17).

3. Antenne selon l'une ou l'autre des revendications précédentes, dans laquelle le répartiteur rayonnant est soit l'un d'un premier répartiteur rayonnant (17) situé à proximité immédiate du premier panneau et d'un deuxième répartiteur rayonnant (19) qui est monté à proximité du premier répartiteur (17) de telle sorte que le premier répartiteur (17) soit interposé entre le deuxième répartiteur et le panneau ; le premier répartiteur rayonnant (17) étant couplé capacitivement aux moyens d'alimentation/réception, le deuxième répartiteur (19) étant couplé électromagnétiquement au premier répartiteur.

4. Antenne selon l'une quelconque des revendications 1 à 3, dans laquelle le répartiteur (17) et l'élément parasite (12) sont définis par des zones métalliques formées sur des surfaces mutuellement opposées d'un panneau de répartition (11).

5. Antenne selon la revendication 4, dépendant de la revendication 2, dans laquelle le panneau de répartition (11) est monté sur le panneau de support (6) espacé parallèlement à celui-ci.

6. Antenne selon la revendication 4 ou 5, dans laquelle la zone métallique définissant l'élément parasite (12) a la forme d'une bande allongée.

7. Antenne selon la revendication 6, dans laquelle la bande allongée (12) est une bande courbe.

8. Antenne selon l'une quelconque des revendications 4 à 7, dans laquelle une zone métallique (17) définissant le répartiteur est couplée capacitivement, par des zones non revêtues (13, 14), à deux zones métalliques revêtues (15, 16) alignées de long d'axes orthogonaux, les zones étant exploitables pour prendre en charge les signaux radio polarisés orthogonalement, les deux zones métalliques revêtues faisant partie des moyens d'alimentation/réception (20, 21, 22, 23, 15, 16).

9. Antenne selon la revendication 8, dépendant de la revendication 7, dans laquelle l'élément parasite (12) est une bande métallique arquée, sous-tendant un angle d'environ 270° disposée symétriquement par rapport à un axe de symétrie du répartiteur rayonnant, lequel axe passe centralement entre lesdites zones métalliques revêtues (15, 16) qui font partie des moyens d'alimentation/réception (20, 21, 22, 23, 15, 16).

10. Antenne selon l'une quelconque des revendications précédentes, dans laquelle le répartiteur rayonnant (17) et l'élément parasite (12) forment un ensemble répartiteur (1) et l'antenne comporte une pluralité de tels ensembles répartiteurs (1, 2, 3, 4).

11. Antenne selon la revendication 10, dans laquelle les moyens d'alimentation/réception ont la forme d'un réseau d'alimentation/réception comportant des pistes conductrices (20, 21, 22, 23) formées par des zones métalliques conductrices déposées sur le panneau.

12. Antenne selon la revendication 11 et comprenant un réseau de quatre ensembles répartiteurs rayonnants et récepteurs séparés (1, 2, 3, 4), lesquels sont capables de prendre en charge deux signaux indépendants et polarisés orthogonalement, deux ports d'entrée (15, 16) étant prévus pour chaque ensemble répartiteur et les ports qui correspondent aux deux polarisations couplant capacitivement les ensembles répartiteurs aux pistes correspondantes (20, 21, 22, 23) du réseau d'alimentation/réception.

13. Antenne selon l'une quelconque des revendications précédentes, dans laquelle l'élément parasite (12) est interposé entre le répartiteur rayonnant et le panneau.

Drawing