Dual band antenna

Information

  • Patent Grant
  • 6396441
  • Patent Number
    6,396,441
  • Date Filed
    Tuesday, November 2, 1999
    25 years ago
  • Date Issued
    Tuesday, May 28, 2002
    22 years ago
Abstract
A dual band antenna is described which comprises a single band antenna surrounded by single band antenna elements. For example, the single band antenna may be a horn operating at a first frequency band and the single band antenna elements may be a flat plate array. In this case, the flat plate array contains an aperture through which the horn extends. The single band antenna and single band antenna elements are positioned such that a transmit and a receive antenna beam are created which have approximately equal phase centres and beamwidths. The single band antenna may also be an array of antenna elements, such as a flat plate array. Alternatively the single band antenna may be formed from dipole elements. As well as this the single band antenna elements may be dipole elements, flat-plate elements or any other suitable type of elements. The dual band antennas described may be used as feeds for reflector antennas or as antennas in their own right. The dual band antennas and feeds described are particularly useful for subscriber satellite communication systems such as satellite TV, with receive signals being in the Ku band and transmit signals being in the Ka band.
Description




BACKGROUND OF THE INVENTION




The invention relates to dual band antennas including but not limited to dual band feeds for reflector antennas. The invention also relates to a carrier casting for a dual band antenna.




Domestic satellite communication antennas are widely used to receive signals such as television broadcasts rather than to transmit as well as receive. However, demand for interactive services such as interactive television and use by small office/home office users has led to the requirement for domestic two-way satellite communication to be provided.




This is possible by using two antennas, one for an up-link or transmission signal and one for a down-link or reception signal. However, this increases the cost of the equipment needed by a subscriber and also increases installation, transport and maintenance costs. The space required for the antennas is also greater and this is a particular problem for domestic applications where space is at a premium.




The up-link and down-link signals are provided at different frequency bands in order that they are readily distinguishable and do not interfere. Antennas which provide two frequency bands are referred to as dual band antennas and a number of different types of dual band antennas are known. However, these suffer from a number of drawbacks when considering subscriber satellite communication systems.




For example, frequency selective surfaces can be used to provide dual bands as in earth station antennas.

FIG. 1

is a schematic diagram showing use of a frequency selective surface


131


. Signals from a transmitter


131


reflect from the frequency selective surface


133


and onto a reflector


130


. However, signals received at a different frequency and reflected from reflector


130


towards the frequency selective surface pass through that surface


131


towards a receiver


132


. That is, the frequency selective surface is arranged to reflect signals of a certain frequency range and transmit others. In this way dual band communication using only one main reflector


130


is possible. However, this type of system is difficult and expensive to install because four components, the transmitter


131


, receiver


132


, frequency selective surface


133


and reflector


130


, must all be correctly aligned. This is difficult to achieve at low cost. Another problem is that cabling must be provided to the transmitter and receiver separately because these have different locations. This also increases installation costs.




Another approach has been to provide a dual band feed for a reflector antenna. For example, this type of system is described in U.S. Pat. No. 4,740,795, Seavey. Two coaxial waveguides are used for the respective two frequency bands and in order that the beamwidth of each beam is similar (and arranged to cover the reflector surface) these waveguides are of different diameter. In order to accommodate this arrangement the design is complex and expensive. In addition, dual band feed systems such as that described in Seavey are not suitable for monopulse alignment methods or for distributed power amplification.




Monopulse alignment methods enable an antenna to be accurately aligned with respect to a satellite and this is particularly important in subscriber satellite communication applications where there is typically little room for alignment error and where costs for an operator to align an antenna are high. Distributed power amplification is advantageous because high power transmit amplifiers are not readily available at millimetric frequencies. In dual band feed systems such as the Seavey system, distributed power amplification is not possible because there is only one transmit antenna element.




U.S. Pat. No. 4,141,012, Hockham et al. describes a dual band waveguide radiating element for an antenna. Using this element an array antenna which operates at two frequencies can be provided. The waveguide element is excited by probe structures entering the guide perpendicular to the plane of the array face. This has significant cost and size implications because the antenna is not a “flat-plate”. Also, in terms of the number of elements being fed the approach described in U.S. Pat. No. 4,141,012 is inefficient.




A general rule in antenna design is that, in order to “focus” the available energy to be transmitted into a narrow beam, a relatively large “aperture” is necessary. The aperture may be provided by a broadside array, a longitudinal array, an actual radiating aperture such as a horn, or by a reflector antenna which, in a receive mode, receives a collimated beam of energy and focuses the energy into a converging beam directed toward a feed antenna, or which, in transmit mode, focuses the diverging energy from a feed antenna into a collimated beam.




Those skilled in the art know that antennas are reciprocal devices, in which the transmitting and receiving characteristics are equivalent. Generally, antenna operation is referred to in terms of either transmission or reception, with the other mode being understood therefrom.




A particular problem with respect to feeds for reflector antennas is that manufacturing costs are relatively high because many parts are required and the overall structure is complex. For example, the structure described in U.S. Pat. No. 4,740,795, Seavey, above is particularly complex and expensive. Often special connectors are required and complex shielding is necessary to prevent leak of electromagnetic radiation. Also, because many different parts are used, each of these has to be tested individually which increases manufacturing time and makes maintenance and repair difficult. These factors increase the cost of feeds which is particularly disadvantageous for domestic systems intended for mass production.




It is accordingly an object of the present invention to provide a dual band antenna which overcomes or at least mitigates one or more of the problems noted above.




Further benefits and advantages of the invention will become apparent from a consideration of the following detailed description given with reference to the accompanying drawings, which specify and show preferred embodiments of the invention.




SUMMARY OF THE INVENTION




According to one aspect of the present invention there is provided a dual band antenna comprising:




(i) a single band antenna arranged to operate in a first frequency band and with a first beamwidth; and




(ii) a plurality of single band antenna elements arranged to operate at a second frequency band; and wherein said single band antenna elements are positioned around said single band antenna such that they operate in use with a second beamwidth similar to said first beamwidth.




This has the advantage that a compact, low cost antenna is provided that operates at two frequency bands. In a preferred embodiment said single band antenna is a horn. This gives the advantage that a simple horn to waveguide transition is achieved which simplifies manufacture and thus reduces costs.




According to a second aspect of the present invention there is provided a dual band feed for a reflector antenna said feed comprising:




(i) a single band antenna arranged to operate in a first frequency band and with a first beamwidth; and




(ii) a plurality of single band antenna elements arranged to operate at a second frequency band; and wherein said single band antenna elements are positioned around said single band antenna such that they operate in use with a second beamwidth similar to said first beamwidth.




This has the advantage that a compact and low cost feed is provided that operates at two frequency bands. Also the feed is suitable for use with a reflector antenna in a subscriber outdoor unit, for example, for an interactive television system.




According to another aspect of the present invention there is provided a reflector antenna comprising a dual band feed, said feed comprising:




(i) a single band antenna arranged to operate in a first frequency band and with a first beamwidth; and




(ii) a plurality of single band antenna elements arranged to operate at a second frequency band; and wherein said single band antenna elements are positioned around said single band antenna such that they operate in use with a second beamwidth similar to said first beamwidth.




In this way a low cost, dual band, compact, reflector antenna is formed that can be used for subscriber satellite communication systems such as satellite television.




According to another aspect of the present invention there is provided a method of operating a dual band antenna as described above said method comprising the steps of:




(i) transmitting information input by a user to a satellite using said single band antenna; and




(ii) receiving signals from said satellite using said single band antenna elements, on the basis of said transmitted information.




This provides the advantage that using the dual band antenna a user is able to communicate with a satellite, for example, in a satellite television system. The user is then able to access communications systems to which the satellite is linked, such as the internet.




According to another aspect of the present invention there is provided a method of operating a reflector antenna as described above said method comprising the steps of:




(i) transmitting information input by a user to a satellite using said single band antenna; and




(ii) receiving signals from said satellite using said single band antenna elements, on the basis of said transmitted information.




According to another aspect of the present invention there is provided a one piece carrier casting arranged to support a first single band antenna and a plurality of single band antenna elements and wherein said carrier casting is sized and shaped to support said single band antenna elements at positions around said first antenna. This provides the advantage that a one-piece structure is provided that is inexpensive to manufacture and which is compact. This structure provides support for component parts of a dual band antenna in a cost effective way.




According to another aspect of the present invention there is provided a dual band feed for a reflector antenna comprising:




(i) A single band antenna;




(ii) A plurality of single band antenna elements;




(iii) A one piece carrier casting arranged to support said single band antenna and said single band antenna elements such that said single band antenna elements are positioned around said single band antenna.




This provides a dual band feed that is compact and inexpensive to manufacture. Because a one piece carrier casting is used the positions of the antenna and antenna elements with respect to one another is easily ensured and this reduces manufacturing costs. The one piece carrier is inexpensive to manufacture using known methods.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

illustrates use of a frequency selective surface in a dual band reflector antenna according to the prior art.





FIG. 2

is an exploded view of a flat-plate antenna array according to the prior art.





FIG. 3

is a perspective view of a subscriber satellite antenna with a reflector and feed.





FIG. 4

is a schematic diagram of a satellite interface terminal.





FIG. 5

is a back view of a flat plate antenna mounted on a support.





FIG. 6

is a side view of the flat plate antenna of FIG.


5


.





FIG. 7

is an exploded schematic diagram of a flat plate array antenna.





FIG. 8

is an exploded schematic diagram of a flat plate array feed for a reflector antenna.





FIG. 9

shows a distribution network for use in the flat plate array antenna of FIG.


7


.





FIG. 10

shows a punched plate for use in the flat plate array antenna of FIG.


7


.





FIG. 11

shows a distribution network for use in the flat plate array antenna of FIG.


7


.





FIG. 12

shows a punched plate for use in the flat plate array antenna of FIG.


7


.





FIG. 13

shows a distribution network for use in the flat plate array antenna of FIG.


7


.





FIG. 14

shows a punched plate for use in the flat plate array antenna of FIG.


7


.





FIG. 15

is an exploded, schematic diagram of a flat plate array feed for a reflector antenna.





FIG. 16

is an exploded, schematic diagram of another flat plate array feed for a reflector antenna.





FIG. 17

is an exploded, schematic diagram of another flat plate array feed for a reflector antenna.





FIG. 18

illustrates the space required for one feed within another feed for a reflector antenna.





FIG. 19

shows a feed for a reflector antenna comprising a horn within another feed.





FIG. 20

is a schematic side view of a horn for use in the feed of FIG.


19


.





FIG. 21

is a schematic plan view of a horn for use in the feed of FIG.


19


.





FIG. 22

is a perspective view of a horn.





FIG. 23

is an end view of a horn.





FIG. 24

shows corner pieces for use in a horn.





FIG. 25

is a side view of a horn and waveguide for use in the feed of FIG.


19


.





FIG. 26

is a plan view of the horn and waveguide of FIG.


25


.





FIG. 27

is a front view of a feed assembly for a reflector antenna.





FIG. 28

is a longitudinal cross section through the assembly of FIG.


27


.





FIG. 29

is a longitudinal cross section through part of the assembly of FIG.


27


.





FIG. 30

is an exploded view of the feed assembly of FIG.


27


.





FIG. 31

is a schematic cross section through part of the feed assembly of FIG.


27


.





FIG. 32

is a block diagram of the components of a dual band antenna.





FIG. 33

shows possible configurations of slots in punched plates for use in feeds for reflector antennas.





FIG. 34

shows the relative positions of slot apertures in a punched plate.





FIG. 35

shows the result of duplicating the slot apertures of FIG.


34


and rotating the duplicate slots 90° with respect to the slots of FIG.


34


.





FIG. 36

shows the relative positions of slot apertures in a punched plate.





FIG. 37

shows slot apertures in a punched plate with cut away portions.





FIG. 38

shows another example of slot apertures in a punched plate with cut away portions.











DETAILED DESCRIPTION OF THE EMBODIMENTS




Embodiments of the present invention are described below by way of example only. These examples represent the best ways of putting the invention into practice that are currently known to the Applicant although they are not the only ways in which this could be achieved.




U.S. Pat. No. 6,175,333, also assigned to Nortel Networks Corporation, describes a dual band flat-plate array antenna for use in a subscriber satellite communication system and the contents of U.S. Pat. No. 6,175,333 are incorporated herein by reference. Whilst the antennas and feeds described in U.S. Pat. No. 6,175,333 are effective and useful, the present application advantageously extends the dual band antenna systems of U.S. Pat. No. 6,175,333 for use under certain circumstances.





FIG. 2

illustrates the structure of a flat-plate array antenna according to the prior art. A back-plate


211


is provided which is made from aluminium or other electrically conducting material. Above the back-plate


211


a power supply circuit plate


212


is placed. This power supply circuit plate


212


is formed from plastics material or other electrically insulating material. On the power supply circuit plate


212


a power supply circuit pattern, or distribution network,


214


of conducting strips is formed for connection to means for controlling the antenna. This pattern


21


forms a type of “tree” structure with many terminations


216


. Each termination


216


is called a “probe” and the probes are arranged in an array. Above the power supply circuit plate


212


a radiation plate


213


or top plate is provided. This is formed from electrically conducting material such as aluminium and contains a plurality of apertures


215


arranged in an array. The array of apertures


215


corresponds to the array of probes in the power supply circuit plate


212


so that when the radiation plate


213


is placed over the power supply circuit plate


212


each probe projects into a region below an aperture


215


. Each probe and aperture combination then forms an antenna element which enables radiation such as signals (of a certain frequency band) from a satellite to be received. That is, this type of flat-plate array only operates for one frequency band according to the size of the apertures


215


in these apertures. The back plate


211


, power supply circuit plate


212


and radiation plate


213


are typically spaced apart using plastic foam inserts (not shown). Downstream of the flat-plate antenna there is connected an electronic device, particularly a converter, which processes the signals according to the particular application. Coupling of the flat-plate antenna and the electronic processor device is in most cases by means of a hollow waveguide with capacitive coupling-in of the radiation summation signal.




The present invention provides a flat-plate antenna array which operates at two frequency bands. For example, a particular embodiment provides a flat-plate antenna for Ka−Ku band satellite communication access units where the transmit (Tx) band is about 29.5 to 30 GHz (Ka band) and the receive (Rx) band is about 10.7 to 12.75 GHz (Ku band).




In the antenna described in U.S. Pat. No. 6,175,333, two superimposed layers of probes and apertures are provided in order to enable a flat-plate antenna to operate at two frequency bands. The apertures in the different layers are effectively superimposed, aligned or positioned in register. However, to form a flat-plate antenna operating with a transmit frequency of 30 GHz and a receive frequency of 12 GHz it is difficult to arrange the required apertures such that they can be superimposed effectively. Also, each layer of probes requires its own distribution network or power supply circuit pattern


214


and this creates a problem because there is limited space. That is, only the probes


216


of the distribution networks should be exposed beneath an aperture


215


and the rest of the distribution network must be contained within the space between the apertures


215


. However, before now this has proved difficult to achieve especially because the spacing between the apertures is required to be less than 1 wavelength in order that grating lobes are not created. As well as this the apertures


215


themselves are preferably about ½ a wavelength in diameter for efficient operation of the antenna.




In the present application, rather than creating dual band antenna elements by superimposing pairs of probes and apertures as in U.S. Pat. No. 6,175,333, two separate sets of single band antenna elements are used. One set of single band antenna elements operates at a transmit frequency band and the other set at a receive frequency band. Each set of single band antenna elements is arranged in a flat plate array structure and the two flat plate arrays are superimposed. However, the antenna elements are positioned within the flat plate arrays such that each antenna element in one flat plate array does not overlie any antenna elements in the lower flat plate array. Then, by removing regions of the upper flat plate array, the antenna elements in the lower flat plate array are able to operate through the upper flat plate array. For example, this can be achieved by making an aperture in the upper flat plate array above each antenna element in the lower flat plate array. Alternatively, regions of the upper flat plate array above antenna elements in the lower flat plate array are cut away.




Because two flat plate arrays are used, two distribution networks are required and both of these must be arranged such that they are confined to areas in-between any apertures in the flat plate arrays. Because more apertures are required to allow the lower flat plate to operate, this restricts the area available for the distribution networks.




In a preferred embodiment, the receive antenna elements are provided with two polarities, such as horizontal and vertically polarised elements, whereas the transmit antenna elements are provided at one polarity such as vertically polarised elements. In this case, three flat plate arrays of elements are provided, one for horizontally polarised receive elements, one for vertically polarised receive elements and one for vertically polarised transmit elements. The three flat plate arrays are superimposed and apertures are formed in the upper flat plate arrays to allow the lower flat plate arrays to operate through the upper layers. It is also possible to use four or more flat plate arrays, following the same principles. However, the number of flat plate arrays that can practically be accommodated is eventually limited by the requirements for the distribution networks and positioning of the antenna elements so that they do not overlie one another.




A dual band array feed for a reflector antenna is also provided using two superimposed arrays of antenna elements operating at different frequency bands, and with apertures (or removed regions) in the upper array allowing elements in the lower array to operate. In this case, the antenna elements must also be arranged such that the transmit and receive antenna beams are of approximately equal beamwidths and have approximately equal phase centres.




In all the embodiments involving feeds for reflector antennas described herein, the dual band feed is arranged to provide a transmit and a receive antenna beam with approximately equal beamwidths and approximately equal phase centres. These beamwidths are arranged such that the surface area of the reflector is effectively covered by each beam whilst at the same time minimising regions of the beam that do not fall onto the reflector in order to prevent loss of energy. It is not essential for the beamwidths to be exactly equal as long as they are arranged such the feed operates practically and effectively. Similarly, the phase centres of the beams do not have to be exactly equal as long as the feed is able to operate practically and effectively.




Referring now to the figures,

FIG. 3

shows a reflector antenna with a reflector


31


and an offset feed unit


32


. The offset feed unit


32


incorporates a dual band feed as described herein and any suitable antenna dish


31


may be used. The antenna dish has a diameter of about 75 cm in a preferred embodiment and the offset feed unit


32


is preferably a single enclosure containing the feed and its required electronics.





FIG. 4

shows an out door unit (ODU)


41


suitable for use at a domestic location to provide an interface to a satellite communication system. In this example, the ODU comprises a reflector antenna, although any suitable type of antenna may be used. An indoor unit


42


is provided that is connected to the ODU via an interface link IFL


43


. For example, the indoor unit may be a set-top box suitable for use with a television in the subscriber's home. By using this interface the subscriber is able to access any communications systems to which the satellite communication system is linked. For example, the internet.





FIGS. 5 and 6

show a flat plate antenna mounted on a support. The flat plate antenna may form the ODU of

FIG. 4

instead of the reflector antenna of FIG.


3


. Flat plate antennas may be housed with their required electronics in one enclosure and this gives the advantage of being aesthetically acceptable and resistant to wind.





FIG. 7

is an exploded view of a dual band flat plate array antenna. In order for the antenna to operate at two frequency bands, two sets of single band antenna elements are provided one for transmitting and one for receiving. Each set of single band antenna elements is provided as part of a flat plate array or triplate


79


,


80


.




Each triplate


79


,


80


comprises a power supply circuit plate


76


,


78


which is formed from plastic film or other suitable electrically insulating material and upon which probes and a distribution network are provided. Any suitable form of probes and distribution network can be used. The probes are connected to each other by stripline sections (not shown) and all the stripline sections are connected to a common stripline feed structure (not shown) in accordance with known techniques to effect reception or transmission of signals in the required frequency bands. Each triplate


79


,


80


also comprises a back plate


71


,


73


which acts to reflect radiation towards the upper layers and out of the flat plate array and a punched plate


72


,


74


which contains an array of apertures


81


. For example, the apertures may be slots or circular holes. The back plate


71


,


73


and punched plates


72


,


74


are ground planes and are formed from aluminium, copper clad Mylar (trade mark) or other suitable material. The plates within each triplate


79


,


80


are spaced apart using foamed plastic spacers


75


or spacers formed from any suitable dielectric material.




Each probe in a distribution network


76


,


78


is positioned so that it falls within one of the apertures in the punched plate


72


,


74


above it, in order to form a single band antenna element. If slots are used in the punched plates


72


,


74


, vertical slots operate for horizontally polarised radiation and horizontal slots operate for vertically polarised radiation.




As shown in

FIG. 7

the triplates


79


,


80


are positioned one above the other. However, this is done such that the antenna elements of one triplate do not overlie the antenna elements of the other triplate. In addition, regions


81


of the upper triplate


78


are removed in order that the antenna elements


83


of the lower triplate are able to radiate through the upper triplate


80


. This is described in more detail with reference to

FIGS. 9

to


14


below.




In a preferred embodiment both horizontally and vertically polarised receive antenna elements are provided together with vertically polarised transmit antenna elements. However, it is not essential to use horizontally and vertically polarised elements in this way. Other types of polarised elements may be used, such as circularly polarised elements. Referring to

FIG. 7

the lowest triplate


79


provides vertically polarised receive antenna elements by virtue of vertical slots


83


in the punched plate


72


. A third triplate or flat plate array is then provided


84


to give horizontally polarised antenna elements at the same frequency band and the antenna elements of the lowest triplate


79


. This is achieved as illustrated in

FIG. 7

by using the punched plate


72


of the lowest triplate


79


as the back plate of the third triplate


84


. A third distribution network is provided on plate


77


and punched plate


73


forms the upper layer of the third triplate


84


. Punched plate


73


contains both horizontal and vertical slots, with the vertical slots being identical to those in the punched plate


72


of the lowest triplate. This allows the antenna elements of the lowest triplate to radiate through the vertical slots in the punched plate


73


of the third triplate. The horizontal and vertical slots in punched plate


73


are of the same size and the array of horizontal slots when rotated 90° corresponds to the array of vertical slots.




As shown in

FIG. 7

the punched plate


74


of the uppermost triplate


80


contains horizontal and vertical slots that are identical to those in the lower triplates. However, it is not essential for these slots to be identical as long as the antenna elements of the lower triplates are able to operate through the upper triplate. In addition, the punched plate


74


of the uppermost triplate


80


contains vertical slots


84


which are smaller than the other slots and form part of the transmit antenna elements. Because the vertical slots


84


are smaller and have a different spacing that the other slots they form antenna elements which operate at a different frequency band.




The uppermost and lowermost triplates


79


,


80


differ from one another in the sizes of the apertures in the punched plates


72


,


74


in order that each triplate operates at a different frequency band. The centre-to-centre spacing between the apertures should be less that one wavelength in order that grating lobes are avoided. However, it is also required to increase the centre-to-centre spacing between the apertures as much as possible in order to increase the space available for the distribution network. For a given triplate, the apertures preferably have a length of about ½ a wavelength, although the apertures are designed to be as small as practically possible for efficient operation of the antenna.




The beamwidth associated with each triplate is related to the wavelength and it is not necessary for these beamwidths to be equal. For example, the transmit beamwidth for a subscriber satellite communication system can be smaller than for the receive beamwidth.




In a particular embodiment the thicknesses of the components in each triplate


79


,


80


,


84


are as follows:






















Back plate




0.6




mm







Plastic foam spacer




1




mm







Power supply circuit layer




0.1




mm







Plastic foam spacer




1




mm







punched plate




0.6




mm















In the example shown in

FIG. 7

, four transmit elements are shown for about every receive element and in this way the gain of the transmit beam exceeds that of the receive beam.




In the embodiment being discussed, the Tx band is about 30 GHz and the Rx band about 12 GHz. This gives a 2:5 ratio in wavelengths between the two bands. This means that the element spacing for the receive elements and the transmit elements should be in approximately the same ratio in order that the spacing is always just less than one wavelength. The grid illustrated in

FIG. 7

has a ratio of 2:1 which is approximately 2:5 and operates satisfactorily. The transmit elements


84


are arranged in a square grid within a larger grid formed by the receive elements


81


,


82


.





FIGS. 9

to


14


illustrate the structure of the triplate layers for one example of a flat plate antenna array.

FIG. 9

shows the form for a first distribution network suitable for use in a lower most triplate of an antenna, for example, layer


76


in FIG.


7


. This first distribution layer


76


is located above a back-plate


71


with a layer of foam


75


in-between. As described above a plurality of probes


90


are provided (sixteen in

FIG. 7

) and these are connected together by stripline sections


91


. In the example shown in

FIG. 7

each probe


90


is positioned parallel with the vertical axis of the page and together the probes form an array. The distribution network is supported on a dielectric sheet or film for example, of plastics material.




Above the first distribution network layer


76


another foam spacer


75


is provided and then a first punched plate


72


which acts as a ground plane. The first punched plate is formed of metal such as aluminium, or alternatively material such as copper clad Mylar (trade mark). An array of apertures


110


is formed in the first punched plate


72


, as shown in FIG.


10


. Each aperture


110


is in the form of a slot but other suitable shapes of aperture may be used as is known in the art. The apertures


110


are positioned such that each one overlaps a probe


90


in the first distribution layer


76


below. This can be see by superimposing

FIGS. 9 and 10

. The slot apertures


110


are positioned parallel to the horizontal axis of the page or flat plate array and so are at 90° to the probes


90


in the lower first distribution layer


76


. Also, in this example, each slot aperture


110


is positioned so that it crosses or overlaps a probe at a location along that probe of approximately ¼ of a wavelength from its end. In this way, each slot aperture


110


and the probe


90


that it overlies form an antenna element that is vertically polarised.




Above the first punched plate


72


illustrated in

FIG. 10

, a foam spacer


75


is provided and above that a second distribution layer


77


. This second distribution layer is illustrated in FIG.


11


and provides sixteen probes ill positioned parallel to the horizontal axis of the page. As for the first distribution layer


76


the probes


111


are connected together by stripline sections and the whole distribution network is supported on a film such as a plastics sheet.




Apertures


112


are provided in the second distribution layer. These apertures


112


correspond in shape, size and position to the apertures


110


in the first punched plate


72


. The second distribution network


77


is arranged so that it does not overlie apertures


110


in the first punched plate. This is achieved by positioning the second distribution network


77


between the apertures


112


in the second distribution layer.




Above the second distribution layer


77


a foam spacer


75


is provided and then a second punched plate


73


. This second punched plate


73


contains slot shaped apertures


113


,


114


and is formed of suitable material in the same way as for the first punched plate


72


. Two sets of slot shaped apertures are provided


113


,


114


with one set


113


corresponding in shape, size and position to the apertures


112


in the second distribution layer and also to the apertures


110


of the first punched plate. The other set


114


of slot shaped apertures is an array of apertures with their longitudinal axes parallel to the vertical axis of the page. This array has the same spacing as the array of the first set of apertures


113


and together the two arrays form a grid structure. The size and shape of the apertures in the two sets


113


,


114


are approximately the same.




The second set of apertures


114


cross over probes


111


in the second distribution network


77


. As for the first triplate


79


, each aperture


114


crosses over a probe


111


with the aperture


114


and probe


111


at 90° to each other. In this way, each aperture


114


and probe


111


together form an antenna element that is horizontally polarised. The second punched plate


73


, second distribution network layer


77


and the first punched plate


72


together form a second triplate


84


. The first punched plate


72


acts as a back plate for this second triplate


84


.




Above the second punched plate


73


a foam spacer


75


is placed and above this a third distribution network


78


which is illustrated in FIG.


13


. An array of probes


115


are provided, again connected by stripline sections. Each probe is positioned with its longitudinal axis parallel to the horizontal axis of the page and in the example shown in

FIG. 13

,


64


probes are provided. This gives four times as many probes as in either of the first or second triplates


79


,


84


. The probes of the third distribution network are also shorter than those of the first and second distribution networks in order the required frequency band is achieved.




Two sets of slot shaped apertures


116


,


117


are provided in the third distribution network


78


. The apertures


116


of one set correspond in shape size and position to the apertures


110


in the first punched plate


72


and the apertures of the other set


117


correspond in shape size and position to the vertically oriented apertures


114


of the second punched plate


73


. As for the first and second distribution networks, the third distribution network is arranged so that it is located between the apertures


116


,


117


.




Above the third distribution network


78


a foam spacer


75


is located and then a third punched plate


74


. This third punched plate contains slot shaped apertures, for example, as shown in FIG.


14


. Of these apertures a plurality


118


,


119


correspond in shape, size and position to those apertures in the second punched plate


73


. The remaining apertures


120


are positioned with their longitudinal axes parallel to the vertical axis of the page. Each of these remaining apertures


120


crosses over a probe


115


in the third distribution network below and is positioned at 90° to the probe


115


that it crosses over. Together each of the remaining apertures


120


and the probe


115


that it crosses over form an antenna element that is horizontally polarised. In a preferred example, these horizontally polarised antenna elements operate at about 30 GHz and the slot size is approximately 5 mm×0.5 mm with a spacing of 9.5 mm.




The third punched plate


74


, third distribution network


78


and second punched plate


73


together form a third triplate


80


. Here the second punched plate


73


acts as a back plate in a flat plate array antenna.




The antenna elements of the first triplate


79


are able to operate through the second and third triplates


84


,


80


because apertures corresponding to those in the first punched plate


72


are provided through the second and third triplates. Similarly, the antenna elements of the second triplate


84


are operable through the third triplate


80


because apertures corresponding to those in the second punched plate


73


are provided through the third triplate.




The arrays of antenna elements in the three triplates


79


,


80


,


84


can be increased by simply extending the arrays as long as the distribution networks can be accommodated in the space available between the required apertures.




The particular sizes, spacings and locations of the apertures and probes in the example discussed above are only one possibility. Alternative arrays of antenna elements may be used according to the frequency bands required. Also, it is not essential to include the second triplate


84


if antenna elements of only one polarisation are required.




Dual Band Feeds for Reflector Antennas




Examples of dual band feeds for reflector antennas are now described. These dual band feeds may also all be used as antennas in their own right. The examples all involve using an array of single band antenna elements of a first frequency band arranged around an antenna with a similar beamwidth as the surrounding array of antenna elements. The central antenna operates at a second frequency band, different from that of the outer array of elements. For example, the central antenna may be a flat plate array, an array of dipole elements, a horn or any other suitable antenna. The outer array of antenna elements may be flat plate elements, dipole elements or any other suitable type of antenna elements. Also, by virtue of the arrangement of the central antenna and the surrounding antenna elements, the two antenna beams produced are approximately concentric such that the dual band antenna operates effectively.




In each of these examples, two antenna beams are created using the array feed, one for an up-link communication channel and one for a down-link communication channel. These antenna beams must have approximately co-incident phase centres and approximately equal beamwidths in order to illuminate a reflector effectively and efficiently. As well as this the array feed should be low cost, enable monopulse alignment methods and distributed power amplification to be used and also be small in size.




Dual Band Flat-plate Array Feed for a Reflector Antenna





FIG. 15

illustrates a dual band flat plate array feed for a reflector antenna that is suitable for providing horizontal and vertical polarised antenna elements for operation at about a 12 GHz receive band and vertical polarised antenna elements for operation at about 30 GHz transmit band. Two triplates are effectively provided


151


,


152


one for receive antenna elements of one polarisation and the other for receive antenna elements of another polarisation and transmit antenna elements.




A first triplate comprises a back-plate


153


, a first distribution network layer


155


and a first punched plate


157


with these layers being spaced apart using foam spacers


15


in a similar way as for the flat plate array antenna described above. The first distribution network provides, for example, six probes connected together using stripline sections. As for the flat plate array antenna described above the probes are of the same size and shape and are arranged in an array with their longitudinal axes being parallel.




The first punched plate


157


contains slot shaped apertures, one for each probe in the first distribution network. The slot shaped apertures are of the same size and shape and are arranged in an array with their longitudinal axes at 90° to the longitudinal axes of the probes in the first distribution network. As for the flat plate array antenna described above the slot shaped apertures cross over probes in the first distribution network to form first antenna elements of either horizontal or vertical polarisation.




Above the first punched plate


157


is a foam spacer


154


and above this a second distribution network


156


. The second distribution network contains one set of probes to form antenna elements which operate at the same frequency but opposite polarisation to the first antenna elements. A second set of probes is also provided in the second distribution network. This second set of probes form part of second antenna elements which operate at a different frequency band from the first antenna elements. As described above for the flat plate array antenna, the second distribution network contains apertures which correspond to those in the first punched plate.




Another foam spacer is placed over the second distribution network and above this a second punched plate


158


. The second punched plate


158


contains slot shaped apertures which correspond to those in the first punched plate. In addition, apertures are provided, to form antenna elements of the same frequency range as the first antenna elements but of an opposite polarisation. Also, apertures are provided to form antenna elements of a different frequency to the first antenna elements.




In one embodiment the slot shaped apertures in the first punched plate are positioned as shown in

FIG. 34

with the horizontal spacing between the centres of the pairs of slot shaped apertures being 0.45 wavelengths and the vertical spacing between the centres of pairs of slot shaped apertures being 0.49 wavelengths. This array design was analysed using LINPLAN (trade mark). The slot dimensions were nominally 1 mm×11 mm and the frequency specified at 12.75 GHz. For the example illustrated in

FIG. 34

, a 3×4 element array was simulated in LINPLAN with an amplitude variation as shown below:











For the azimuth radiation pattern cut LINPLAN indicated that the 10 dB beamwidth was 59° and the highest sidelobe level−18.97 dB. For the elevation radiation the 10 dB beamwidth was 61° and the highest sidelobe level −23.86 dB. The directivity was 13.64 dBi.




These slots in the first punched plate are used to form either horizontally or vertically polarised receive elements. In order to form antenna elements of the opposite polarisation, slots are provided in the second punched plate. These slots in the second punched plate form an array which corresponds to the array of apertures in the first punched plate with a 90° rotation.

FIG. 35

shows the result of repeating the array of slots from the first punched plate, rotating these 90° and combining these with the first array of slots. It can be seen that the slots overlap one another as shown at A in FIG.


35


. This is not desirable because any antenna elements in a triplate below the punched plate will not radiate through the covering slots efficiently. The inter-slot spacing was adjusted to remove the overlapping regions and also to maximise the space between the slots which is available for accommodating the distribution or beamformer network. In this way the arrangement shown in

FIG. 36

was obtained. Here the horizontal distance between the central vertical slots has been increased from 0.45 wavelengths to 0.55 wavelengths. Similarly, the vertical distance between the central horizontal slots has been increased from 0.45 wavelengths to 0.55 wavelengths. In order to maintain the outer dimensions of the array, and consequently the beamwidth, these increases in spacing are counteracted by decreases in spacing between the outer vertical elements (the horizontal distance between these is now 0.4 wavelengths) and between the outer horizontal elements (the vertical distance between these is now 0.4 wavelengths).




In a preferred embodiment of the flat plate array feed, the arrangement of slots shown in

FIG. 36

is used for the horizontally and vertically polarised receive antenna elements. An amplitude taper (in volts) is applied to this array as follows:























0




0.85




0.85




0







1




0




0




1







0




0.85




0.85




0















Using LINPLAN to analyse the arrangement illustrated in

FIG. 36

, together with the amplitude taper described above, the following results were obtained for a frequency of 12.75 GHz. For a pattern cut of 0° the 10° beamwidth was 55° and the highest sidelobe level −18.72 dB. For a pattern cut of 90° the 10° beamwidth was 55° and the highest sidelobe level−11.05 dB. The directivity was 13.22 dBi. With a frequency of 11.725 GHz the 10° beamwidths were 59° for both the 0° and 90° pattern cuts. This illustrates the effect of frequency on the beamwidth.




In the embodiment where the arrangement of slots for the receive antenna elements is as shown in

FIG. 36

, the slots for the transmit band antenna elements are conveniently located within the centre of the array of receive antenna slots. This is illustrated schematically in

FIG. 15

on the second punched plate


158


. That is, the arrangement of slots for the receive antenna elements as shown in

FIG. 36

is particularly advantageous because it allows room for transmit band antenna elements. It is not essential to use slot shaped apertures; any suitable shape of apertures such as circular apertures can be used in the arrangement shown in FIG.


36


. The receive (or transmit) antenna elements are positioned in a cross like formation such that the elements do not overlap and such that a region in the centre of the cross is available for transmit (or receive) band antenna elements.




Other arrangements for the receive and transmit element slots are possible.

FIGS. 33

A to D shows possible arrangements for horizontal and vertically polarised antenna element slots. Arrangement C has already been discussed above. In each of these arrangements, slots for the transmit elements need to be incorporated whilst allowing enough space to accommodate the required distribution networks. Also, the transmit element slot array should be arranged such that it is approximately concentric with the receive element slot array in order that the antenna beams have co-incident phase centres.





FIG. 16

illustrates an alternative embodiment of the flat plate array feed for a reflector antenna.

FIG. 16

shows a flat plate array feed which is similar to that of

FIG. 15

except that three triplates,


161


,


162


,


163


are used. Also, the upper two triplates


162


,


163


contain a central aperture


16


extending through their centres. The antenna elements of the lowest triplate


161


are positioned below the central aperture


164


in order that the lowest triplate


161


is operable through the other triplates. In this way the size of the lowest triplate


161


can be varied as long as its antenna elements are below the central aperture


164


. One upper triplate


162


provides antenna elements that are polarised in one direction and the other upper triplate


163


provides antenna elements that are polarised in the other direction. Also, as in the flat plate antenna array discussed above, apertures in upper triplates are used to allow antenna elements in lower triplates to operate through the upper layers. The same positioning of slot shaped apertures in the punched plates may be used as for the embodiment of

FIG. 15

except that the antenna elements of different frequencies are separated into separate triplates.





FIG. 17

illustrates another embodiment of a flat plate array feed for a reflector antenna. This is similar to the embodiment of

FIG. 16

but with the order of the triplates changed. Again three triplates


171


,


172


,


173


are used. This time, the lower triplates


172


,


173


contain a central aperture


164


extending through these plates. The upper triplate


171


is positioned above the central aperture


164


and thus is not practically affected by antenna elements in the lower triplates.




In the flat plate feeds discussed above, it is also possible to use cut away portions in the punched plate of the uppermost triplate. For example, in the example shown in

FIG. 15

, the uppermost punched plate


158


may take the form illustrated in

FIG. 37

or that illustrated in FIG.


38


. In

FIG. 15

the six vertical slots of the outer array do not form antenna elements as such but rather allow antenna elements from the lower triplate to operate. However, the six horizontal slots of the outer array do form antenna elements. These six horizontal slots


3700


are present in the punched plates shown in

FIGS. 37 and 38

. However, instead of providing vertical slots as such the punched plates of

FIGS. 37 and 38

have cut away portions


3701


which extend over the area that the vertical slots would have been in. These cut away portions can also be thought of as regions of the upper punched plate that have been removed.




In the flat plate feeds discussed above, tapering of the illumination may be employed in order to equalise the beamwidths, as is known in the art.




For the flat plate feeds discussed above the problem of providing enough space between the antenna elements in order to accommodate the distribution network arises again as for the flat plate antenna array described above. However, this problem is not quite so acute because the array feed is small so that the distribution network can be accommodated to some extent in the area around the outside of the array feed. As for the flat plate antenna array the spacing between the elements should be less that one wavelength in order that grating lobes are not created. Because the array feed is smaller than the array for the flat plate antenna discussed above, grating lobes occur for element spacings that are further from one wavelength than would otherwise have been the case. As for the flat plate antenna the aperture sizes are preferably about ½ a wavelength but again should be as small as possible to accommodate the distribution network.




Although the examples of dual band array feeds for reflector antennas discussed above have been described for providing frequency bands of about 30 GHz and 12 GHz, the arrangements can be used for any combination of frequency bands.




Monopulse alignment is possible with the antennas described above because multiple receive antenna elements are available. Also, distributed power amplification is possible with the reflector antennas described above because multiple transmit antenna elements are available.




Dual Band Array Feed for a Reflector Antenna Comprising Dipole Antenna Elements




It is also possible to replace some or all of the flat-plate antenna elements in the array feeds discussed above with dipole or other suitable antenna elements. For example, an array of six dipole elements arranged in the positions of the slots in

FIG. 36

may be used with a further array of dipole elements of a different frequency located in the centre of the arrangement of six dipole elements. Dipole elements are stood off from a ground plane as is known in the art. Similarly, an array of six dipole elements arranged in the positions of the slots in

FIG. 36

may be used with a further array of single band flat plate antenna elements located in the centre of the arrangement of six dipole elements. Alternatively, an array of dipole elements may be used in the centre with an array of six flat plate elements in the positions of the slots in FIG.


36


. Any suitable type of antenna element may be used in place of some or all of the dipole elements in these examples. Also, it is not essential to use only six elements in the outer array. More than six elements may be used. In these examples involving dipole elements it is not essential to use six elements; other numbers and arrangements of elements may be used as discussed above for the dual band flat plate array feeds. Also, the feeds which include dipoles may be used as antennas in their own right.




Combined Horn and Flat Plate Array




It is also possible to combine a horn antenna with a flat plate array to produce a dual band antenna or a feed for a dual band reflector antenna. In the arrangement of slots in

FIG. 36

it can be seen that a relatively large rectangular space is available in the centre of the array of slots. In the feeds for reflector antennas discussed above, this space was exploited to locate an array of flat plate antenna elements of a different frequency. However, this space also accommodates a horn as illustrated in

FIGS. 18 and 19

.




The arrangement of slots from

FIG. 36

is repeated in

FIGS. 18 and 19

.

FIG. 18

illustrates the size of the space in the centre of the array of slots in one example where X′=11.94 mm; Y′=13.94 mm and Z′=13.94 mm. Rectangle


180


represents the aperture of a rectangular horn whose width, Y=14.5 mm and height, Z=20.3 mm. It can be seen from

FIG. 18

that the corners of the horn overlap the slot apertures at A. In order to avoid this, the horn


181


is shaped to fit around the slot apertures as illustrated in FIG.


19


.




In one example, a horn and waveguide for operation at about 30 GHz are used. In this case the dimensions of the horn and waveguide are given below with reference to FIGS.


20


and


21


: b=3.55 mm; b


1


=14.5 mm; ρ


e


=42.68 mm; ρ


1


=42.05 mm; Ψ


e


=9.78°; p


e


=p


h


=31.76 mm; a=7.1 mm; a


1


=20.3 mm; ρ


h


=42.68 mm; Ψ


h


=11.7°.




A comparison of the performance of a horn with these dimensions and an equivalent horn with the corners adapted to fit around the slot elements was made. These horns were soldered together in parts as illustrated in FIG.


22


and to one horn, corner pieces were added.

FIG. 23

shows the front face of a horn with added corner pieces


190


. These corner pieces


190


were machined into the horn and formed as wedge shaped pieces positioned to taper into the horn aperture.

FIG. 24

shows the form of the tapered corner pieces


190


.

FIGS. 25 and 26

show the form of the horn and illustrate how each horn is fed by a waveguide


191


which terminates with a flange


192


. Radiation pattern cuts were obtained for the two horns in an anechoic chamber and it was found that little difference in performance resulted from modifying the corners of the horn. Good sidelobe performance was obtained with an acceptable 10 dB beamwidth at approximately 60°.




As mentioned above coupling of a flat-plate antenna and its electronic processor device is in most cases by means of a hollow waveguide with capacitive coupling-in of the radiation summation signal. In the arrangement discussed above, using a horn combined with a flat plate array, the advantage of a relatively simple transition from the horn to a hollow waveguide is obtained.




The combined horn and flat plate array arrangement discussed above may either be used as a dual band antenna in its own right or as a feed for a dual band reflector antenna.




In a preferred embodiment the horn is used for the transmit band at about 30 GHz and the flat plate array is used for a receive band at about 12 GHz. Because the flat plate array comprises a plurality of receive antenna elements the advantage of being able to use monopulse alignment methods is attained.




Combined Horn and Dipole Array




It is also possible to create a dual band feed for a reflector antenna using a horn and a dipole array. In this case, an array of single band dipole antenna elements are arranged around a horn of a second frequency band. The horn and array of dipole elements are arranged to give similar beamwidths and to have coincident phase centres. This arrangement is also functional as a dual band antenna in its own right rather than as a feed. In a preferred example, the flat plate antenna elements in the example discussed above are replaced by dipole elements. For example, the slot elements of

FIG. 19

are replaced by dipole elements. This enables more space within the arrangement of dipole elements to be obtained so that it is not essential to remove the corners of the horn as described above. Similarly, other types of antenna element besides dipole and flat plate elements may be used in combination with a horn.




In the examples discussed above which use triplates, it is possible to include connections between two ground planes of a triplate. For example, in the case shown in

FIG. 7

, the lowermost triplate


79


has a back plate


71


and a punched plate


72


which are two ground planes of the triplate. The connections act as short circuits between two ground planes and provide suppression of parallel plate modes as is known in the art. It is not essential to include these connections however. The connections are most effective when positioned in the vicinity of slot or other apertures of antenna elements in the triplate but it is not essential to locate the connections near apertures.





FIG. 8

shows a dual band antenna which comprises an antenna


85


arranged to operate at in a first frequency band and with a first beamwidth; and a plurality of single band antenna elements


86


arranged to operate at a second frequency band; and wherein said single band antenna elements


86


are positioned around said antenna


85


such that they operate in use with a second beamwidth similar to said first beamwidth.




Construction of Feed Assembly





FIGS. 27

to


31


illustrate how the combined horn and flat plate array are incorporated into a feed assembly for a reflector antenna such as that illustrated in

FIG. 3. A

cylindrical housing


270


is provided for the feed assembly and a top view of this housing is shown in FIG.


27


. The housing


270


is formed of plastics material or any other suitable material. The dimensions shown in

FIGS. 27 and 28

are examples only; other dimensions may be used.





FIG. 28

is a longitudinal cross section through the assembly of

FIG. 27. A

connector


271


is provided at one end on the cylindrical housing for connecting the feed assembly to a cable which in turn is connected to an indoor unit such as a set-top box in a subscriber's premises. The cylindrical housing


270


has a cover


272


below which a feed assembly


273


is located.

FIG. 29

is a longitudinal cross section through this feed assembly and shows a flat plate array


274


positioned to lie parallel to the housing cover


272


, and a horn


275


with a waveguide


276


connected to it. Two further waveguides


277


are provided for connection to the flat plate array


274


although only one of these is visible in FIG.


29


. The waveguide


277


that is not visible in

FIG. 29

is located underneath the visible waveguide that connects to the flat plate array. One of these waveguides provides a connection between antenna elements of one polarisation in the flat plate array


274


and the other waveguide for antenna elements of another polarisation. Thus it is not essential to use two such waveguides. Probes for connecting the flat plate array


274


to the two waveguides are provided, as is known in the art, but are not shown in the Figures. Also “top hats” (not shown) are positioned over these waveguides


274


(as known in the art) to prevent these emitting radiation out of the cover of the feed assembly.





FIG. 30

is an exploded view of the feed assembly of FIG.


27


. This shows how the feed assembly


273


is inserted into the housing


270


and the cover


272


positioned. The flat plate array


274


is also shown as being supported on a carrier casting


278


within which the horn


275


and waveguides


276


,


277


are supported. Each waveguide


276


,


277


is connected to a printed circuit board via a probe. The printed circuit boards


279


are positioned parallel to the waveguides as shown and screening cans


280


are placed around the printed circuit boards to prevent escape of electromagnetic radiation.





FIG. 31

is a schematic cross section through part of the feed assembly of FIG.


27


. It shows way in which the printed circuit boards


279


and screening cans


280


may be fitted directly to the carrier casting


278


. Also, the waveguide probes


281


are shown.




By using a single casting


278


to carry the horn


275


, waveguides


276


,


277


, flat plate array


274


and printed circuit boards


279


a simple design is achieved which is easy to manufacture and which is low cost. The one part casting is compact and can be quickly tested compared to alternative structures which use several components. The casting provides a dual function of supporting both the dual band antenna and its associated electronics and using the carrier casting


278


it is ensured that the horn


275


and flat plate array


274


are correctly positioned with respect to one another. The carrier casting


278


is easily formed as a single piece and holes or apertures are then drilled into this single piece using known manufacturing methods which are inexpensive. No special connectors are required to connect the horn, waveguides or flat plate array to the carrier casting; rather conventional low cost fixing means are used where required. As well as this, once the flat plate array


274


, horn


275


, waveguides


276


,


277


and electronics are carried by the casting these items are easily slipped into a protective cover or housing


270


as illustrated in FIG.


30


.




Another advantage is that by positioning the screening cans


280


over the printed circuit boards


279


and by using the protective housing


270


and cover


272


, unwanted electromagnetic emissions from the assembly are reduced.




Components of Dual Band Antenna





FIG. 32

is a block diagram of the components of a dual band antenna and is applicable to the flat plate array embodiments, the flat plate array feed embodiments and the combined horn and flat plate array embodiments discussed above. Although

FIG. 32

includes a block labelled “reflector and mounting”, this block is not essential.




A flat plate array block


340


is shown and this represents either a flat plate array or a flat plate array and horn combination as described above. The flat plate array block


340


is connected to a low noise block


341


by two waveguides


342


, one for horizontally polarised signals and one for vertically polarised signals. The low noise block is used as known in the art, to convert the amplitude of the signals received by the flat plate array block


340


in order to make these signals suitable for input to a subscriber indoor unit. The low noise block


341


is located towards the front of the assembly, near the flat plate array block


340


, in order to reduce signal losses.




The low noise block


341


is in turn connected to an interface


343


which further converts the signals from the flat plate array block


340


in order to make these compatible with a subscriber's indoor unit, such as a TV receiver. Output from the interface to the subscriber's indoor unit is via a cable


345


, for example, an F-type, coaxial cable connector. The interface


343


also has a connection


346


to a power supply, for example this may be a DC connector.




The assembly also contains a reference oscillator


347


, a control unit


348


and a power unit


349


which are conventional units used as is known in the art.




The interface


343


also has another output which connects to a transmitter unit


350


which in turn is connected to the flat plate array block


340


. In the case that a subscriber wishes to transmit a signal, for example, to request a web page or to request a particular television programme, the subscriber makes an input to the indoor unit. For example, this may be done using a remote control unit for a television set, which sends information about the user input via a set-top box and connection


345


to the interface


343


. The user input is sent to the transmit unit


350


and converted into the appropriate type of signal before being transmitted using the flat plate array block


340


. The transmitted signal is received by a satellite communication or other type of communication system.




In the event that signals are receive at the flat plate array block


340


, for example, from a satellite communication system, these signals are processed by the low noise block


341


, interface


343


and other units in the assembly before being passed to the subscriber's indoor unit via cable


345


.




A range of applications are within the scope of the invention. These include situations in which it is required to form a dual band flat plate array antenna or a dual band flat plate array feed for a reflector antenna. These antennas and feeds may be used for two-way satellite communication such as interactive television. The range of applications also includes terrestrial communication systems and any application where it is required to provide dual band communication for example, two-way satellite communication.



Claims
  • 1. A dual band antenna comprising:(i) a single band antenna arranged to operate in a first frequency band and with a first beamwidth; and (ii) a plurality of single band, directly radiating, antenna elements arranged to operate at a second frequency band; and wherein said single band antenna elements are positioned around said single band antenna such that they operate together in use with a second beamwidth approximately equal to said first beamwidth; and wherein said plurality of single band antenna elements comprise a flat-plate array comprising a distribution network layer comprising a plurality of probes co-planar with the distribution network layer; said distribution layer being positioned under, substantially parallel to, and spaced apart from a plate of electrically conducting material comprising a plurality of apertures positioned such that each aperture is above a probe; said single band antenna and single band antenna elements having substantially co-planar radiating apertures together forming an aperture of the dual band antenna, and said flat-plate array and distribution network layer being substantially parallel to said aperture of the dual band antenna.
  • 2. A dual band antenna as claimed in claim 1 wherein said single band antenna comprises a horn.
  • 3. A dual band antenna as claimed in claim 1 wherein said single band antenna comprises an array of antenna elements.
  • 4. A dual band antenna as claimed in claim 1 wherein said single band antenna comprises a flat-plate array.
  • 5. A dual band antenna as claimed in claim 1 wherein said plurality of single band antenna elements are dipole elements.
  • 6. A dual band antenna as claimed in claim 1 wherein said flat plate array contains an aperture and wherein said single band antenna is a horn extending through said aperture.
  • 7. A dual band antenna as claimed in claim 1 wherein said single band antenna elements comprise a first plurality of single band antenna elements polarised in a first direction and a second plurality of single band antenna elements polarised in a second direction different from the first direction.
  • 8. A dual band antenna as claimed in claim 1 wherein said flat plate array comprises a first flat plate array of first single band antenna elements polarised in a first direction and a second flat plate array of second single band antenna elements polarised in a second direction.
  • 9. A dual band antenna as claimed in claim 8 wherein said first and second flat plate arrays are superimposed such that antenna elements of one flat plate array overlie regions of the other flat plate array between antenna elements.
  • 10. A dual band antenna as claimed in claim 9 which further comprises one or more apertures or cut-away regions in one of said flat plate arrays, said apertures or cut-away regions being positioned over antenna elements in the other flat plate array.
  • 11. A dual band antenna as claimed in claim 1 wherein said single band antenna is arranged to transmit signals and said single band antenna elements are arranged to receive signals.
  • 12. A dual band antenna as claimed in claim 1 wherein said single band antenna is operable in the Ka frequency band and said single band antenna elements are operable in the Ku frequency band.
  • 13. A dual band antenna as claimed in claim 1 which comprises a one piece carrier casting arranged to support said single band antenna and said single band antenna elements.
  • 14. A method of operating a dual band antenna as claimed in claim 1 said method comprising the steps of:(i) transmitting information input by a user to a satellite using said single band antenna; and (ii) receiving signals from said satellite using said single band antenna elements, on the basis of said transmitted information.
  • 15. A dual band feed for a reflector antenna said feed comprising:(i) a single band antenna arranged to operate in a first frequency band and with a first beamwidth; and (ii) a plurality of single band, directly radiating, antenna elements arranged to operate at a second frequency band; and wherein said single band antenna elements are positioned around said antenna such that they operate together in use with a second beamwidth approximately equal to said first beamwidth; and wherein said plurality of single band antenna elements comprise a flat-plate array comprising a distribution network layer comprising a plurality of probes co-planar with the distribution network layer; said distribution network layer being positioned under, substantially parallel to, and spaced apart from a plate of electrically conducting material comprising a plurality of apertures positioned such that each aperture is above a probe; said single band antenna and single band antenna elements having substantially co-planar radiating apertures together forming an aperture of the dual band antenna, and said flat-plate array and distribution network layer being substantially parallel to said aperture of the dual band antenna.
  • 16. A feed as claimed in claim 15 wherein said single band antenna comprises a horn.
  • 17. A feed as claimed in claim 15 wherein said single band antenna comprises an array of antenna elements.
  • 18. A feed as claimed in claim 15 wherein said single band antenna comprises a flat-plate array.
  • 19. A feed as claimed in claim 15 wherein said plurality of single band antenna elements are dipole elements.
  • 20. A feed as claimed in claim 15 wherein said flat plate array contains an aperture and wherein said single band antenna is a horn which extends through said aperture.
  • 21. A feed as claimed in claim 15 wherein said single band antenna elements comprise a first plurality of single band antenna elements polarised in a first direction and a second plurality of single band antenna elements polarised in a second direction different from the first direction.
  • 22. A feed as claimed in claim 15 wherein said flat plate array comprises a first flat plate array of first single band antenna elements polarised in a first direction and a second flat plate array of second single band antenna elements polarised in a second direction.
  • 23. A feed as claimed in claim 22 wherein said first and second flat plate arrays are superimposed such that antenna elements of one flat plate array overlie regions of the other flat plate array between antenna elements.
  • 24. A feed as claimed in claim 23 which further comprises one or more apertures or cut-away regions in one of said flat plate arrays said apertures or cut-away regions being positioned over antenna elements in the other flat plate array.
  • 25. A feed as claimed in claim 15 wherein said single band antenna is arranged to transmit signals and said single band antenna elements are arranged to receive signals.
  • 26. A feed as claimed in claim 15 wherein said single band antenna is operable in the Ka frequency band and said single band antenna elements are operable in the Ku frequency band.
  • 27. A feed as claimed in claim 15 which comprises 12 single band antenna elements.
  • 28. A feed as claimed in claim 15 wherein the geometric arrangement of said single band antenna and single band antenna elements is such that in use a receive and a transmit antenna beam are provided with approximately equal phase centres.
  • 29. A feed as claimed in claim 15 which further comprises a one piece carrier casting arranged to support said single band antenna and said single band antenna elements.
  • 30. A feed as claimed in claim 29 wherein said one piece carrier casting comprises a hollow region arranged to support said single band antenna.
  • 31. A reflector antenna comprising a dual band feed, said feed comprising:(i) a single band antenna arranged to operate in a first frequency band and with a first beamwidth; and (ii) a plurality of single band, directly radiating, antenna elements arranged to operate at a second frequency band; and wherein said single band antenna elements are positioned around said antenna such that they operate together in use with a second beamwidth approximately equal to said first beamwidth; and wherein said plurality of single band antenna elements comprise a flat-plate array comprising a distribution network layer comprising a plurality of probes co-planar with the distribution network layer; said distribution network layer being positioned under, substantially parallel to, and spaced apart from a plate of electrically conducting material comprising a plurality of apertures positioned such that each aperture is above a probe; said single band antenna and single band antenna elements having substantially co-planar radiating apertures together forming an aperture of the dual band antenna, and said flat-plate array and distribution network layer being substantially parallel to said aperture of the dual band antenna.
  • 32. A method of operating a reflector antenna as claimed in claim 31 said method comprising the steps of:(i) transmitting information input by a user to a satellite using said single band antenna; and (ii) receiving signals from said satellite using said single band antenna elements, on the basis of said transmitted information.
  • 33. A one piece carrier casting arranged to support a first single band antenna and a plurality of single band, directly radiating, antenna elements and wherein said carrier casting is sized and shaped to support said single band antenna elements at positions around said first antenna such that they operate together in use with a second beamwidth approximately equal to said first beamwidth; and wherein said plurality of single band antenna elements comprise a flat-plate array comprising a distribution network layer comprising a plurality of probes co-planar with the distribution network layer; said distribution network layer being positioned under, substantially parallel to, and spaced apart from a plate of electrically conducting material comprising a plurality of apertures positioned such that each aperture is above a probe; said single band antenna and single band antenna elements having substantially co-planar radiating apertures together forming an aperture of the dual band antenna, and said flat-plate array and distribution network layer being substantially parallel to said aperture of the dual band antenna.
  • 34. A casting as claimed in claim 33 which comprises a mouthed hollow region arranged to support said first single band antenna.
  • 35. A casting as claimed in claim 34 which comprises a substantially flat surface around the mouth of said hollow region wherein said substantially flat surface is arranged to support said single band antenna elements.
  • 36. A dual band feed for a reflector antenna comprising:(i) a single band antenna; (ii) a plurality of single band, directly radiating, antenna elements which comprise a flat-plate array comprising a distribution network layer comprising a plurality of probes co-planar with the distribution network layer; said distribution network layer being positioned under, substantially parallel to, and spaced apart from a plate of electrically conducting material comprising a plurality of apertures positioned such that each aperture is above a probe; said single band antenna and single band antenna elements having substantially co-planar radiating apertures together forming an aperture of the dual band antenna, and said flat-plate array and distribution network layer being substantially parallel to said aperture of the dual band antenna; and (iii) a one piece carrier casting arranged to support said single band antenna and said single band antenna elements such that said single band antenna elements are positioned around said single band antenna and such that they operate together in use with a second beamwidth approximately equal to said first beamwidth.
  • 37. A dual band feed as claimed in claim 36 wherein said single band antenna is a horn.
  • 38. A dual band feed as claimed in claim 37 wherein said one piece carrier casting comprises a hollow region arranged to support said horn.
  • 39. A dual band feed as claimed in claim 36 further comprising a printed circuit board and wherein said one piece carrier casting is arranged to support said printed circuit board.
  • 40. A dual band feed as claimed in claim 36 further comprising a waveguide connected to said single band antenna and wherein said one piece carrier casting comprises a hollow region arranged to support said waveguide.
  • 41. A dual band feed as claimed in claim 36 wherein said one piece carrier casting comprises a substantially flat surface arranged to support said single band antenna elements.
US Referenced Citations (3)
Number Name Date Kind
4141012 Hockham et al. Feb 1979 A
4623894 Lee et al. Nov 1986 A
4740795 Seavey Apr 1988 A
Foreign Referenced Citations (2)
Number Date Country
0463649 Jan 1992 EP
2241832 Mar 1994 GB