Antenna, antenna base station and method of use

Abstract

Directional antenna (200) comprising a horn coupled orthomode transducer, comprising a horn (204) and an orthomode transducer (e.g planar OMT 201) including a first antenna element (206), comprising a

Description

Technical Field of the Invention This invention relates to the field of antennas, and antenna base stations, in particular to antennas that operate at dual polarisation and over a broad frequency range with consistent radiation patterns. Background to the Invention The development of antennas and associated technology has enabled wireless communications to become prevalent in modern society. The wireless signal environment is however becoming ever more contested with transmissions, with the demands on data transfer rates and bandwidth continually increasing. In an effort to meet these demands, additional communications 'channels' are being implemented in wireless communication systems through use of spatially separated or dual polarised antennas, and the use of new frequencies of operation for example, those in the 5G band. This can however come at the expense of having to design bespoke antennas and systems to operate within those frequency bands or certain modes of operation. Antennas used in communications devices which use dual polarisation offer two independent communications channels, which can help to improve the data transfer rate. A dual polarised antenna may be manufactured using multiple orthogonal antenna elements, however ensuring that these systems operate effectively over a wide frequency range or can be 'broadband' is complex. Devices exist, for example GB2598442A that utilise a conventional dual-polarised antenna design in a base station that provide a level of performance over a narrower frequency range. Therefore it is an aim of the present invention to provide an alternate dual polarised antenna and base station that mitigates these issues, in particular in the 5G band. Summary of the Invention According to a first aspect of the invention there is a directional antenna comprising a horn coupled orthomode transducer, comprising a horn and an orthomode transducer, wherein the orthomode transducer further comprises a first antenna element comprising a first antenna feed and coupling means, and a second antenna element comprising a second antenna feed and coupling means, wherein the first and second coupling means are arranged to couple a signal to the horn. A directional antenna has a directional radiation patterns, and is capable of sending or receiving signals at individual frequencies or more preferably across a range of frequencies or bands, for example those used across communications and telecommunications commonly within a typical range of around 300MHzto 5 GHz, including those standards often commonly referred to as 2G, 3G, 4G and more recently 5G. These are commonly known as RadioFrequency (RF) signals however, some frequencies of operation may also include frequencies considered to be in the microwave region of the electromagnetic spectrum. The inventor has shown that the antenna of the present invention is particularly advantageous when operating at the higher frequency range between 3GHz - 5GHz referred to as 5G. The radiation patterns of the antenna describe the directional or angular performance to both send and receive signals. Directional antennas have a radiation pattern such that they emit directionally, transmitting energy into a specific or preferred direction, the directionality is often referred to as the main lobe, the main lobe which provides the directionality and peak performance, will also have a beam width which defines how much of a geometric space or volume the main lobe or beam extends to. For example with a spherical coordinate system the energy may be directed into a hemispherical lobe, or may be further directed into a volume having a smaller solid angle, for example a truncated cone. Where more than one antenna is used individual antenna elements may have a different radiation patterns to each other, or may alternatively have substantially the same radiation patterns. The directional antenna comprises a horn coupled OrthoMode Transducer (OMT). An OMT is an antenna feed element capable of sending or receiving signals of orthogonal polarisations. The OMT comprises a first antenna element arranged to transmit or receive signals at a first polarisation and a second antenna element arranged to transmit or receive signals at a second polarisation. It is the relative arrangement of the two antenna elements which determine the performance or sensitivity in sending and receiving signals having orthogonal polarisation. It will be clear to the skilled person that this includes arrangements which are substantially orthogonal as these will still provide a level of performance in sending and receiving signals which are orthogonally polarised. However the inventor has shown that by arranging the antenna elements such as to be orthogonal, performance may be optimised as this has advantageously been shown to reduce interference or cross talk between the antenna elements. Each of the first and second antenna elements comprises a respective feed and signal coupling means. In this context the feed and coupling means are used in both transmit and receive modes. The feed may be any transmission line or cable suitable for transmitting the Radiofrequency signal. The coupling means may be any suitable means for coupling the signal to the horn. A horn coupled OMT differs from a conventional dual-polarised antenna, including dipole antennas in that the antenna elements are not fed from the centre of the antenna element, instead the antenna elements are designed to excite fields at the base of the horn, via the respective feeds and the signal coupling means, being fed from the outer edges or periphery of the antenna element. The horn may be any know in the art for directing signals away from or into the antenna elements. For example, being substantially funnel shaped or flared, typically having a first end with a narrower cross-section closest or adjacent the antenna element of the OMT and a second end having a wider section furthermost from the antenna elements of the OMT, referred to as the radiating aperture. Having a surface or wall formed between the two ends. It is known that horns may also have a conical shape, having circular cross section when viewed in a plan view, or pyramidal shape, having square or rectangular cross section in plan view, but variations of these are also well known. The angle or shape of the inner surface of the horn is commonly known as the flare angle, and may take a linear form between the two ends, such as the case of a conical or pyramidal cone, or non-linearly, for example the surface taking on a curved path, such as a parabolic, logarithmic or exponential curve. The inventor has shown that the combination of the Orthomode Transducer (OMT) with the horn has shown the advantage of increased data transfer rates for an antenna element, as a result of being dual-polarised, and having a directional radiation pattern with low levels of distortion across a broad frequency range or bands, useful to a range of communications applications including for example telecommunications, in particular the combination has been shown to provide improved performance in the 5G band over conventional antennas and base stations. In certain embodiments of the antenna the orthomode transducer (OMT) is substantially planar. Substantially planar, takes its normal meaning in that the antenna elements extend in a plane, having a finite thickness. The planar antenna element includes at least the first and second antenna elements and their respective feeds and coupling means, but may also include additional aspects of the device, for example an electrical isolation means or ground plane. This advantageously achieves an optimal low profile design for the antenna elements. In some embodimentsthe coupling means of the first and second antenna elements comprise first and second probe elements arranged with a separation gap therebetween. Each antenna element has a coupling means comprising a first and second probe, which may be a pair of substantially identical probes. The inventor has shown that substantially identical probes provide optimal performance. Probe elements are single ended antenna elements extending from the respective feed such that the radiated signals are coupled to the horn. The coupling is achieved by ensuring that the arrangement of the probes is such that they extend into a central aperture or hollow part of the antenna element. So for example given a conical horn, which when viewed in plan view would be a circle the probes would be arranged such that they extend beyond the inner circumference of the horn such that signals may be transmitted and received. The probes of the first and second antenna element are arranged to radiate signals of orthogonal polarisation, for example by being arranged such that each pair are substantially orthogonal with respects each other. Advantageously being able to alter the geometry of the probes simplifies manufacture and allows for configurability to the antenna with respect the frequencies of operation such as by altering or adjusting the dimensions and or shape of the probe elements. The probe may take any geometric shape, but are preferably elongated such as rectangular. The inventor has shown that elongate probes advantageously improve performance particularly in the 5G band. In preferred embodiments, the directional antenna further comprises an electrical isolation means, the electrical isolation means being arranged between the first antenna element and its respective feed and the second antenna element and its respective feed. The electrical isolation means ensures that there is no direct electrical pathway between the first antenna element's respective feed and coupling means and the second antenna element's respective feed and coupling means. It may be any suitable electrical isolation or insulation means such as a material with insulating properties, preferably the material has a dielectric constant less than 3, and may be a single isolation means or equally may be a plurality of isolation means. The electrical isolation means advantageously improves performance of the antenna by reducing unwanted interference. In some preferred embodiments the electrical isolation means comprises a layer of electrically insulating substrate. The layer of insulating substrate may be planar having a finite thickness. It may be entirely formed from insulating material or may alternatively be an insulating substrate deposited or attached to some other material. The isolation means may be a single layer of substrate or deposited material, or may be formed from multiple layers having other materials between. The use of an electrical insulating substrate provides the advantage that the substrate can be chosen to provide configurability to the antenna element with respect to the electrical and radiative performance of the antenna elements. A further advantage is that an electrically insulating substrate also provides a layer of material to which the respective feed elements and coupling means may be optionally attached. In certain embodiments of the invention comprising an isolation means, the directional antenna further comprises a ground plane arranged between the respective first antenna element and its respective feed and coupling means and the second antenna element and its respective feed and coupling means. The ground plane is an electrically conducting material which provides the electrical ground. The first and second antenna elements are separated from each other and the ground plane by the isolation means, such that there is no direct electrical pathway between the first and second antenna elements and or the ground plane. The ground plane has an aperture or hole through its surface configured to align to the position of the antenna signal coupling means such that the signals can pass freely through the ground plane without interference, as such the aperture may simply be a hole or alternatively may be formed from electrically transparent materials which do not interfere with the coupling of the signals with the horn. For example the ground plane may be formed from copper having a hole at its centre aligned with the OMT probes, or alternatively this hole may be filled with a dielectric medium with low relative permittivity, for example being less than 3. The ground plane may be a separate part or layer of the device or alternatively may be incorporated into other parts or layers of the device such as the isolation means. For example if the ground plane were a metal, for example a copper sheet, it could be coated with an isolation means or insulating layer on either or both sides. The ground plane advantageously reduces interaction of the two antenna elements and reduces cross-talk between the orthogonal states in the device, thus further improving performance of the system. In certain embodiments of the invention comprising an isolation means and ground plane, the respective feeds comprise a microstrip transmission line, this type of feed is known in the art. The two microstrip transmission lines on either side of the ground plane and electrically isolated from each other and the ground plane by the isolation means, advantageously allows for simplification of the circuit design as there is no requirement to design complex electrical bridging or crossing of feed lines or having to provide separate grounds for each feed element. In some embodiments of the directional antenna the orthomode transducer is arranged in a stacked configuration, arranged to have the first antenna element, comprising the first feed and coupling means, adjacent to a first electrical isolation means, adjacent to the ground plane, adjacent to a second electrical isolation means, adjacent to the second antenna element, comprising the second feed and coupling means. Stacked configuration means that each layer is adjacent the next. The respective feed and radiation means of each antenna element may be directly laid or attached to the respective isolation means. Furthermore the insolation means may be a separate individual layer or for example may be a layer or coating applied on or to the ground plane. The ground plane may be a single layer common between both the first and second antenna elements. This staked configuration advantageously provides for a compact antenna structure, with optimised performance, when used with the horn of the invention. In certain embodiments the directional antenna further comprises a backshort. The backshort blocks or prevents signals from being sent or received from one side of the device. Typically it is positioned to be on the opposite face of the directional antenna to the horn. The backshort can be dimensioned such as to optimise performance across the band or frequencies of expected operation of the antenna, by varying the height, depth or distance that the backshort is from the surface of the antenna element, typically having dimensions relating to a whole or fraction of the wavelengths and hence frequencies of operation. The use of a backshort advantageously means the signals are directed into a preferentially direction, further improving performance and efficiency. In certain embodiments the horn of the directional antenna comprises a substantially circular first end and a substantially rectangular second end connected by a peripheral wall, wherein the first end is located adjacent the first antenna element. The horn when viewed in plan, has a circular first end forming an opening closest or adjacent the directional antenna element, and a rectangular second end, furthest from the directional antenna element, often referred to as the horn aperture. The peripheral wall connects these two which may take a linear or curved shape, forms an internal surface through which the signals propagate and an external surface. This shape has advantageously been shown to produce larger beam widths or radiation patterns, which provide greater angular coverage, when compared with other horn designs used with the same antenna element configuration. In some embodiments the antenna further comprises an enclosure for screening the respective antenna feeds from directly emitting or receiving radiation, the enclosure further comprising at least a first aperture for receiving the horn. The enclosure is made from any material suitable for providing electromagnetic screening, for example it may be a material such as plastics coated or metalised to provide the required electrical properties. In this context screening means the prevention or reducing or blocking of signals either transmitted or received from directly interacting with the respective feeds of each antenna element. The enclosure may be formed in parts which are brought together, using suitable fastening means such as friction fit, adhesives or other suitable known fasting means, such that when complete, provide the required screening. The enclosure has at least a first aperture for receiving the horn, which allows for the signals from the coupling means to send or receive signals, such that the primary route for signal propagation is through coupling with the horn via the coupling means. The aperture may be matched in dimension and shape to that of the base of the horn, so that the horn may be received into said aperture, for example where the horn has a circular base end, the end closest the antenna element, the aperture in the enclosure would also have a circular cross section. The enclosure may optionally have a second aperture for receiving the optional backshort of the directional antenna. The enclosure advantageously reduces the coupling of the respective feeds of each antenna element to the transmitted and received signals but also provides physical protection to the antenna elements to prevent damage. In certain embodiments of the antenna the horn and at least a first part of the enclosure are formed as a single piece. Formed means that the horn and the at least first part of the enclosure are a single piece. For example where the horn and enclosure were made of metal they could be stamped, pressed or drawn from a single sheet of metal, or may be made using additive or 3D printing techniques with a suitable material. This advantageously simplifies the manufacturing process, and having components with fewer joints provides a more robust and reliable device. In some embodiments of the antenna the backshort and at least a first part of the enclosure are formed as a single piece. Formed means that the backshort and the at least first part of the enclosure are a single piece. For example where the backshort and enclosure were made of metal they could be stamped, pressed or drawn from a single sheet of metal or may be made using additive or 3D printing techniques with suitable material. This advantageously simplifies the manufacturing process, and having components with fewer joints provides a more robust device. More preferably the enclosure is formed from metal. Metal has been shown to provide both good screening and grounding properties also having good strength to weight properties. Metals have conductive properties which mean they are particularly suited to the purpose. In some embodiments of the antenna the enclosure contains the orthomode transducer. This provides the advantage of a packaged antenna element where the often fragile elements are protected from environmental effects. "Contains" take its normal meaning in that the orthomode transducer and their respective elements are substantially held within or covered by the enclosure. In this context "substantially" refers to the fact that features such as an electrical connection means may be on the periphery or external to the enclosure to allow the antenna elements to be powered and controlled, without having to open or access the internal parts of the antenna, furthermore it also refers to the fact that the enclosure may have an aperture or hole to allow the signals to couple to the horn. In preferred embodiments having an enclosure, the enclosure further comprises support means for supporting the first and second antenna elements. This advantageously helps to fix or hold the antenna elements of the OMT in place ensuring their alignment to provide predictable and consistent performance. The support means are any suitable means within the enclosure which restrict the motion of the antenna elements and help locate them within the enclosure. They may be formed directly in the enclosure or may be separate parts or fixing means. In some embodiments the antenna further comprises powering means for powering the directional antennas. Any suitable powering means may be considered which provide an input signal into the antenna. This may be through a suitable connector or cable. According to a second aspect of the invention there is a base station antenna comprising a plurality of directional antennas of the first aspect of the invention. Base station antennas provide a hub or base for wireless signals to be sent and received, they may operate at a single frequency or may be switchable between a plurality of frequencies covering one or many bands or groups of frequencies. A base station includes a plurality of antenna elements to improve performance. The antenna elements are arranged such that the direction of peak performance or main lobe is substantially away from a base station central axis, the central axis being defined as that which is substantially between the antenna elements. For example with a base station having four directional antennas of the first aspect of the invention each having a main lobe the distributed array would position the antenna elements so they are substantially at 90 degrees to their neighbouring antenna element, with the lobe direction away from the base station central axis, such that the beams overlap and thus the radiation patterns would provide substantially omnidirectional performance 360 degrees around and away from the central axis when measured in the plane. It will be clear that the arrangement of the directional antenna in a distributed array can be configured for any given radiation pattern or number of antenna such as to optimise the performance. The inventor has shown that three directional antennas comprising horn coupled OMTs of the first aspect of the invention, arranged equidistantly around the central axis advantageously provides omnidirectional performance whilst minimising the number of the antenna elements required, thus minimising complexity, cost and space required for the overall base station. In certain embodiments of second aspect each of the directional antennas of the first aspect are arranged in an array around and having their respective horns pointing away from, an axis central to the base station, the directional antennas having radiation patterns such that when combined, deliveran overall omnidirectional performance. A base station contains a plurality of directional antennas to improve performance with respect to coverage, and radiated power output. When designing and powering an antenna there is typically a trade-off between coverage (also referred to as directionality) and sensitivity (or related, gain). For example, a given amount of radiative power can either be used to provide broad geometric or spatial coverage, with a certain level of gain, or alternatively higher gain with increased directionality (reduced spatial coverage). As such in the present invention omnidirectional performance in a base station is achieved by physically arranging or positioning each of the plurality of directional antennas in an array around an axis central to the base station, such that their respective radiation patterns in combination provide omnidirectional performance. In this context omnidirectional is taken to mean that radiative performance is substantially equal for a given angle around the central base station axis as measured within a horizontal plane. So for example a base station may provide an output having a spherical output, or alternatively hemispherical output. Furthermore it may have when viewed in three dimensions, a toroidal output, all of these outputs would satisfy being omnidirectional. A base station comprising Horn coupled OMTs of the first aspect of the invention shows the 11 advantage of having good omnidirectional performance across multiple frequencies important to wireless communications, in particular those in the 5G band. In certain embodiments of second aspect, the base station comprises three directional antennas of the first aspect arranged equally spaced array around and having their respective horns pointing away from, an axis central to the base station. The inventor has shown that this advantageously provides omnidirectional performance whilst keeping the number of antenna required to a minimum, hence reducing cost and complexity of the system. According to a third aspect of the invention there is provided a method of using the base station of the first aspect, the method comprising the steps of, providing the base station of any one of the first aspect of the invention and then transmitting or receiving a signal using at least one of the directional antennas. This use advantageously allows for the base station to provide consistent performance over a wide range of frequencies, particularly in the 5G band, whilst also allowing the base station to operate like a directional antenna. This allows the user to selectively send or receive signals in certain directions. The antenna elements of the base station may be used individually or in combination to achieve different levels of angular coverage or directionality. In preferred embodiments of the third aspect the method step of transmitting or receiving a signal comprises transmitting or receiving a signal using all of the directional antennas such that the signal is transmitted or received in an omnidirectional manner. This may be achieved, for example by providing signals having no time delay between them. This advantageously provides a base station with omnidirectional performance across a broad range of frequencies, especially those in 5G band. According to a forth aspect of the invention there is a method for manufacturing a base station antenna comprising the steps of, providing a plurality of directional antennas comprising horn coupled orthomode transducers, arranging each of the plurality of the directional antennas in an array around and having their respective horns pointing away from, an axis central to the base station antenna. This method has been shown to provide a base 12 station having good omnidirectional performance or coverage, across a broad frequency range, in particular the 5G band. In certain embodiments of the forth aspect, the step of providing each of the plurality of directional antennas further comprises, arranging a first feed and coupling means onto an insulating layer to form a first planar antenna element, arranging a second feed and coupling means onto a second insulating layer to form a second planar antenna element, providing a planarground plane and arranging the first planar antenna element, ground plane and second planar antenna element in a stacked configuration, such that feed and coupling means of the respective first and second planar antennas are electrically isolated from each other and the ground plane, providing a horn and arranging said horn to be adjacent the coupling means of the first antenna element. The stacked configuration has the ground plane arranged between the first and second planar antenna, such that the insulating layer or material is adjacent to the ground plane and the feed and coupling means are electrically isolated from each other and the ground plane. This method of manufacture has been shown to produce a compact antenna for use in the base station having good omnidirectional performance across a broad frequency range, in particular the 5G band. In certain embodiments the method of manufacture further comprises providing an enclosure and arranging the first and second planar antenna element and ground plane within said enclosure. This method has been shown to produce a robust antenna element for use in the base station. Any feature in one aspect of the invention may be applied to any other aspects of the invention, in any appropriate combination. In particular device aspects may be applied to method or use aspects and vice versa. The invention extends to a device, use and method of manufacture, substantially as herein described, with reference to the accompanying description. In all aspects, the invention may comprise, consist essentially of, or consist of any feature or combination of features. Brief Description of the Drawings Embodiments of the invention will now be described byway of example only and with reference to the accompanying drawings, in which: Figure 1 illustrates a prior art dual polarised base station. Figure 2 illustrates an exploded view of an embodiment of the directional antenna of the first aspect of the invention Figure 3a illustrates the three dimensional illustration of an embodiment of the directional antenna as arranged in a base station of the second aspect of the invention. Figure 3b illustrates the same embodiment of figure 3a but in plan view. Figure 4a illustrates a typical performance of an embodiment of the base station antenna of the second aspect of the invetion, operating in directional mode. Figure 4b illustrates a typical performance of the same embodiment of 3a in omnidirectional mode. Figure 5a illustrates a three dimensional illustration of two embodiments of the first aspect of the invention having different horn designs. Figure 5b illustrates the performance of the same embodiments of figure 5a. Detailed Description Figure 1 illustrates a prior art base station antenna (100) with three dipole antennas (101a, 101b, 101c) having dual polarisation, the dipoles are driven from centre feeds. The antenna elements are arranged around a central axis, at higher frequencies uniformity or consistency of performance is reduced, the prior art provides an alternative approach to providing performance at higher frequencies by use of parasitic beam focussing element (103). Figure 2 shows an exploded view of an embodiment of the horn coupled OMT(200) of the directional antenna of the first aspect. The OMT (201) comprises an enclosure formed from metal, having been made in two halves, an enclosure top (202) and enclosure bottom (203), the enclosure is approximately 155mm in diameter. The enclosure top (202) has a circular aperture to which the horn (204), also been formed from metal, is attached by interference fit. The horn (204) has a circular first end and a second end having a square cross section with a width of about 70mm. The first end substantially matches the aperture in the enclosure top (202). Between the two ends of the horn is a wall which takes a non-linear shape. The bottom enclosure (203) similarly has an aperture to which a backshort (218) has been fixedly attached. The OMT (201) is a planar OMT having a first (206) and second (207) planar antenna element arranged orthogonally such that they emit / receive orthogonally polarised radiation. Each of the first (206) and second (207) planar antenna elements comprises a coupling means in the form of a first and second pair of probe elements (205) with respective first (210) and second feeds (211) arranged on respective first isolation means (213) and second isolation means (214). Each pair of probe elements (205) have a gap therebetween (212) of approximately 35mm and the probe element (205) end sections have a width of approximately 10mm and length of about 15mm. The OMT (201) has a first (213) and second (214) substrate layer being approximately 0.5mm thick and having a dielectric constant of about 2.2, which acts as an isolation means. The OMT (201) further comprises a ground plane (215) made from metal arranged between the first and second planar antenna elements. The first (213) and second (214) substrate layers have arc cuts (216) which allow the backshort (218) and horn (204) to be in contact with the ground plane (215). The top (202) and bottom (203) enclosure has a raised lip (217) or edge such as to hold the first and second substrate when the device is constructed. Figure 3a illustrates the three dimensional illustration of an embodiment of the horn coupled OMT (301) as arranged in a base station (300) of the second aspect of the invention. The horn coupled OMT (301) of figures 3a are shown having an enclosure made of metal (302), a horn (303) with a circular first end and a square second end connected via a non-linear wall. A first pair of probe antenna elements (304) can be seen with the substrate behind (305). Also shown are the connectors (306) for the input / output signals. Figure 3b illustrates the same arrangement as figure 3b, similarly numbered features are the same as 3a. The metal backshort (310) is also illustrated. Figure 4a shows the performance of the embodiment of 3a and 3b when the base station antenna is used in a directional mode (400). Here only two of the three horn coupled OMTS are used at the same time in combination. Shows operation in a radial plot over 3GHz (401), 4GHz (402) and 5GHz (403) which are relevant to the 5G band. Figure 4b shows the performance of the embodiment of 3a and 3b when the base station antenna is used in an omni-directional mode (420). Here the output in a radial plot of all three horn coupled OMTs are combined. Shows operation over 3GHz (421), 4GHz (422) and 5GHz (423) which are relevant to the 5G band. Figure 5a illustrates a three dimensional illustration of two embodiments having different horn designs, the first OMT (500) having a horn (501) where the first (502) and second (503) end are circular and the joining wall (504) or surface is substantially linear. The second OMT (520) having a horn (521) with a first circular end (523) and a square second end (522) and the joining wall (524) or surface is non-linear, taking a curved path. Figure 5b illustrates the performance of the same embodiments of figure 5a. The first illustration (550) shows the omnidirectional performance of the OMT (not shown) having a horn (not shown) with a circular second end (552) and the OMT (not shown) having a horn with a square second end (551). The second illustration (560) shows the directional performance of same embodiments of figure 5a, again having a horn (not shown) with a circular second end (561) and a horn (not shown) with a square second end (562).

Claims

1. A directional antenna comprising a horn coupled orthomode transducer, comprising a horn and an orthomode transducer, wherein the orthomode transducer comprises a first antenna element, comprising a first antenna feed and coupling means, and a second antenna element comprising a second antenna feed and coupling means, wherein the first and second coupling means are arranged to couple a signal to the horn.

2. The directional antenna of claim 1 wherein the orthomode transducer is substantially planar.

3. The directional antenna of any preceding claim wherein each coupling means of the first and second antenna elements comprise first and second probe elements arranged with a separation gap therebetween.

4. The directional antenna of any preceding claim comprising an electrical isolation means, the electrical isolation means being arranged between the first antenna element and its respective feed and coupling means and the second antenna element and its respective feed and coupling means.

5. The directional antenna of claim 4 wherein the electrical isolation means comprises a layer of electrically insulating substrate.

6. The directional antenna of claims 4-5, further comprising a ground plane, arranged between the respective first antenna element and electrical isolation means and the second antenna element.

7. The directional antenna of claim 6, wherein the orthomode transducer is arranged in a stacked configuration, arranged to have the first antenna element, comprising the first feed and coupling means, adjacent to a first electrical isolation means, adjacentto the ground plane, adjacent to a second electrical isolation means, adjacent to the second antenna element, comprising the second feed and coupling means.

8. The directional antenna of any preceding claim, wherein the horn comprises a substantially circular first end and a substantially rectangular second end connected by a peripheral wall, wherein the first end is located adjacent the first antenna element.

9. The directional antenna of any preceding claim wherein the directional antenna further comprises an enclosure for screening the respective antenna feeds from directly emitting or receiving radiation, the enclosure further comprising at least a first aperture for receiving the horn.

10. The directional antenna of claim 9 wherein the enclosure is formed from metal.

11. The directional antenna of any claims 9 or 10 wherein the enclosure contains the orthomode transducer of the directional antenna.

12. The directional antenna of claims 9-11, wherein the enclosure further comprises support means for supporting the first and second antenna elements.

13. A base station antenna comprising a plurality of the directional antenna of any preceding claim.

14. The base station antenna of claim 13, wherein each of the plurality of directional antennas are arranged in an array around and having their respective horns pointing away from, an axis central to the base station, the directional antennas having radiation patterns such that when combined, deliver an overall omnidirectional performance.

15. A method of using the base station of claims 13-14, the method comprising the steps of:a) Providing the base station of any of claims 13-14; and thenb) Transmitting or receiving a signal using at least one of the directional antennas.

16. The method of claim 15, wherein the step of transmitting or receiving a signal comprises:a) Transmitting or receiving a signal using all of the directional antennas, such that the signal is transmitted or received in an omnidirectional manner.

17. A method of manufacturing the directional antenna of claims 7 or 8a) arranging a first feed and coupling means onto a first insulating layer to form a first planar antenna element;b) arranging a second feed and coupling means onto a second insulating layertoform a second planar antenna element;c) arranging the first planar antenna element to be orthogonal to the second planar antennas element;d) providing a planar ground plane; ande) arranging the first planar antenna element, ground plane and second planar antenna element in a stacked configuration, such that feed and coupling means of the respective first and second planar antennas are electrically isolated from each other and the ground plane;f) providing a horn and arranging said horn to be adjacent the coupling means of the first antenna element.19

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