Self-grounded antenna arrangement

Abstract

A self-grounded antenna arrangement includes a base or central portion in a first plane and a number of arm sections associated with the central portion that taper toward a respective end tip. Each arm section is adapted to form a transition from the central portion and being bent backward toward the central portion by more than 180 degrees so that its end tip approaches a first side of the central portion, at an opening in the central portion. The end tip is connected to a feeder configured to feed, via an arm-section-specific port, one specific port for each arm section. Each arm section has a mixed functionality of a curved monopole antenna and a loop antenna, and the antenna arrangement provides substantially uncoupled ports with far-field functions that are almost orthogonal in polarization, direction, or shape. The arrangement finds use in multiple-input multiple-output antenna systems for statistical multipath environments.

Claims

1. A self-grounded antenna arrangement, comprising: at least one central portion arranged in a first plane and configured to operate as a ground; and at least one arm section associated with the at least one central portion, each arm section tapering toward a respective end tip, comprising an electrically conducting material, being adapted to form a transition from the at least one central portion, being bent backward toward the at least one central portion by more than 180, and having its end tip approaching the at least one central portion on a side thereof at an opening in the at least one central portion, the end tip further being adapted to be connected to a feeding port, a respective feeding port being provided for each arm section, whereby the arrangement has a mixed functionality of a curved monopole antenna and a loop antenna; wherein the arrangement comprises at least two first arm sections; tips of the at least two first arm sections approach the at least one central portion on a same side of the at least one central portion at a distance from each other; the feeding ports for each of the at least two arm sections are substantially uncoupled such that their far-field patterns are substantially orthogonal in either polarization, direction, or shape; and the first arm sections are diametrically symmetrically disposed for reducing coupling between the feeding ports.

2. The antenna arrangement of claim 1, wherein the arrangement comprises a respective central portion for each arm section, thereby forming a combination of a single monopole antenna and a loop, each respective central portion forming a ground plane of the respective monopole antenna.

3. The antenna arrangement of claim 1, wherein the at least one central portion forms a ground plane of the arrangement, one central portion of the at least one central portion is common for a plurality of arm sections, and the at least one central portion comprises a circuit board.

4. The antenna arrangement of claim 1, wherein the arrangement comprises at least one set of three arm sections having tips which approach a central portion on a same side of the central portion, the central portion being triangular.

5. The antenna arrangement of claim 1, wherein the arrangement is an ultra-wideband antenna arrangement.

6. The antenna arrangement of claim 1, wherein the arrangement is included in a wireless communication system.

7. The antenna arrangement of claim 1, wherein the feeding ports of the first arm sections are located either on a side of the at least one central portion that is the same as the side of the at least one central portion that the first arm sections are located or on a same free outer edge of the central portion, and a central conductor connecting the tips and the feeding ports is arranged on the opposite side of the at least one central portion.

8. The antenna arrangement of claim 1, wherein the arrangement comprises at least one second arm section, the tip of which is adapted to approach the at least one central portion at a side that is opposite to the side on which the tips of the at least two first arm sections approach the at least one central portion; for the first and second arm sections, separate ports are arranged on the same or different sides of the at least one central portion or at the same or different outer edges of the at least one central portion.

9. The antenna arrangement of claim 1, wherein the arrangement is configured for attachment to a mast and has a substantially spherical combined radiation pattern.

10. The antenna arrangement of claim 1, wherein the arrangement has a substantially hemispherical combined radiation pattern.

11. The antenna arrangement of claim 1, wherein each arm section is integral with a respective central portion.

12. The antenna arrangement of claim 1, wherein an arm section comprises an element connected to a central portion.

13. The antenna arrangement of claim 1, wherein each arm section symmetrically tapers towards its end tip, with outer edges tapering along respective straight lines substantially as an isosceles triangle, bent to a location at a first distance from a first plane formed by the at least one central portion where the end tip ends from a top limiting plane at a second distance from the at least one central portion forming the first plane, the second distance being larger than the first distance.

14. The antenna arrangement of claim 1, wherein each arm section tapers towards its end tip, with outer edges tapering along curved lines, in a manner of a spherical or hyperbolic triangle, from a top limiting plane at a first distance from and parallel to a first plane formed by the at least one central portion to an end tip location at a second distance from the first plane that is smaller than the first distance.

15. The antenna arrangement of claim 1, wherein a space between the at least one central portion and either a conductor or an arm section on a respective side of the at least one central portion is filled with a dielectric material.

16. A multiple self-grounded antenna arrangement, comprising at least two antenna arrangements of claim 1, the at least two antenna arrangements being adjacent one another substantially in a same plane or along a surface and so that the feeding ports are at outer side edges of respective at least one central portions.

17. A self-grounded antenna arrangement, comprising: at least one central portion arranged in a first plane and configured to operate as a ground; and at least one arm section associated with the at least one central portion, each arm section tapering toward a respective end tip, comprising an electrically conducting material, being adapted to form a transition from the at least one central portion, being bent backward toward the at least one central portion by more than 180, and having its end tip approaching the at least one central portion on a side thereof at an opening in the at least one central portion, the end tip further being adapted to be connected to a feeding port, a respective feeding port being provided for each arm section, whereby the arrangement has a mixed functionality of a curved monopole antenna and a loop antenna; wherein the feeding ports comprise coaxial connectors with center conductors that connect microstrip transmission lines to respective end tips, the microstrip transmission lines are arranged on a printed circuit board located on a side of the at least one central portion that is opposite to the side on which an arm section corresponding to the at least one central portion is bent backward, and either arm section end tips are fed via respective openings in the at least one central portion or a plurality of arm section end tips are fed via a common opening in the at least one central portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will in the following be further described in a non-limiting manner, and with reference to the accompanying drawings, in which:

(2) FIG. 1 is a view of an antenna arrangement according to a first embodiment of the present invention with four antenna ports,

(3) FIG. 1A is a side view of the arrangement in FIG. 1,

(4) FIG. 1B shows an arrangement as in FIG. 1 which is slightly modified,

(5) FIG. 2 shows a second embodiment of an antenna arrangement according to the invention,

(6) FIG. 3 is a view of a third embodiment of an arrangement according to the invention here, also with four antenna ports,

(7) FIG. 3A is a top view of the arrangement of FIG. 3,

(8) FIG. 4 is a view of a fourth embodiment comprising an antenna arrangement with two antenna ports,

(9) FIG. 5 is a schematic view of a fifth embodiment comprising an arrangement with two arms,

(10) FIG. 6 schematically illustrates an arrangement according to the invention suitable for mounting on a wall,

(11) FIG. 7 schematically illustrates another arrangement according to the invention which comprises two antenna structures and which is suitable for wall mounting,

(12) FIG. 8 schematically illustrates another embodiment of an arrangement comprising two antenna structures and which also is suitable for wall mounting,

(13) FIG. 9A schematically, in perspective, illustrates still another embodiment with four ports comprising an arrangement with hemi-spherical coverage suitable for mounting e.g. on a wall,

(14) FIG. 9B is a top view of the arrangement in FIG. 9A,

(15) FIG. 10 illustrates an embodiment with an antenna arrangement comprising one port and a single arm section,

(16) FIG. 11 shows still another embodiment of an arrangement comprising four arms and corresponding ports,

(17) FIG. 12A is a top view of an arrangement comprising three arms and three ports,

(18) FIG. 12B is a perspective view of the arrangement shown in FIG. 12A,

(19) FIG. 13 schematically illustrates an arrangement with spherical coverage and which is suitable for mounting on a mast,

(20) FIG. 13A is a top view of the arrangement in FIG. 13.

DETAILED DESCRIPTION

(21) FIG. 1 shows a first embodiment of a bow-tie antenna arrangement 10 according to the invention. The bow-tie antenna arrangement 10 comprises four arm sections 1, 2, 3, 4 which are so arranged that two arm sections 1, 2 are bent backwards towards one another on a first, here denoted upper for reasons of definition only, side 5.sub.1 of a central portion 5. In this embodiment they are bent so that end tips of the arm sections point towards the center of said upper side 5.sub.1. The end tips are connected to connector pins 6.sub.1, 6.sub.2 which via separate openings 7.sub.1, 7.sub.2 are connected to conductors 21, 22 (dashed lines) located on the opposite (lower) side of the central portion 5, and directed towards opposite side edges of the central portion 5.

(22) In one advantageous embodiment the central portion comprises a circuit board with micro-strip conductors. The conductors 23, 24 of the arm sections 3, 4, which are bent backwards towards the center on the other, second, side of the central portion 5, are located on the first side 5.sub.1 of the central portion and extend in substantially opposite directions towards outer side edges of the central portion. Ports 11.sub.1-11.sub.4, here comprising coaxial connectors, are attached to the side edges, for arm sections 2, 3 on one side edge and for arm sections 1, 4 on the opposite side edge.

(23) The central portion 5 comprises a metal layer 9, on part of the surfaces of which dielectric layers forming printed circuit boards 9.sub.1, 9.sub.2 are disposed. The first arm sections 1, 2 are diametrically arranged with respect to one another and are bent backwards towards the openings arranged substantially at the center of the first side 5.sub.1 of the central portion. The second arm sections 3, 4 are diametrically and symmetrically located with respect to one another and bent backwards towards the center of the second side of the central portion.

(24) In this embodiment the first arm section 1 and the second arm section 3 are located side by side, but bent backwards onto opposite sides or surfaces of the central portion. Correspondingly the first arm section 2 and the second arm section 4 are located side by side and bent backwards onto opposite sides or surfaces of the central portion. In this manner a very weak coupling between the ports 31, 32, 33, 34 is obtained, which is extremely advantageous for MIMO systems. Hence, although the antenna elements formed by the respective arm sections and the central portion are located very close to one another, a very low correlation between the ports is obtained, in particular embodiments even below 0.1 over the range 0.4-16 GHz, which is an extremely good performance. Particularly due to the fact that the arrangement is mainly made by a metal piece, the ohmic losses will be very low.

(25) From the side view of the antenna arrangement shown in FIG. 1A can be seen how the first arm sections 1, 2 are bent backwards towards the first, here upper, side 5.sub.1 of the central portion whereas the second arm portions 3, 4 are bent backwards towards the second side 5.sub.2 of the central portion 5. The end tips of the arm sections are connected to connector pins 6.sub.1, 6.sub.2, 6.sub.3, 6.sub.4 via respective openings connecting to microstrip conductors on the respective opposite sides of the central portion.

(26) In the embodiment of FIG. 1A the dielectric layers 9.sub.1, 9.sub.2 do not extend throughout the surfaces of the metal layer 9 towards the transition regions where the arm sections comprise partial extensions of the central portion. It should be clear, however, that the dielectric layers alternatively could be arranged over the entire surfaces or to any desired extent thereupon. The arrangement 10 comprises arm sections 1, 2, 3, 4, made in one piece with the central portion 5. In alternative embodiments the arm sections comprise sections which are fixedly or demountably connected to the central portion.

(27) FIG. 1B shows an antenna arrangement 10 only differing from the arrangement shown in FIG. 1 in that instead of having separate openings in the central portion for each arm section connector pin, there is a common opening 7 for all connector pins. Other elements bear the same reference signs as in FIG. 1 but are provided with a prime symbol.

(28) FIG. 2 illustrates an antenna arrangement 20 also comprising four arm sections 1A, 2A, 3A, 4A as in FIG. 1. Elements similar to elements shown in FIGS. 1, 1A are given the same reference numerals but with an index A. In the arrangement 20 the conductor elements 21A, 22A, 23A, 24A are all arranged to be directed towards the same side edge of the central portion 5A enabling the provisioning of connectors, e.g. coaxial connectors 11A.sub.1-11A.sub.4 on one and the same outer edge of the antenna, which in some embodiments is practical for mounting and access purposes. It should be clear that instead of being edge mounted, the connectors can be mounted on the first and second sides or surfaces 5A.sub.1, 5A.sub.2 respectively, or in any appropriate manner; the invention is not limited to any particular type of connectors or connector locations.

(29) The antenna arrangement 30 shown in FIG. 3 also comprises four arm sections 1B, 2B, 3B, 4B extending from a central portion 5B which are diametrically and pairwise bent backwards onto a first side 5B.sub.1 and onto a second side 5B.sub.2 respectively. The arm sections have a shape tapering towards the end tips in a non-symmetric manner, starting with a rapidly tapering region after which the respective arm section is narrow and tapers regularly and approaches the central portion such that the surfaces of the narrow sections facing away from the central portion are substantially planar, and form substantially constant angles with the central portion first and second sides 5B.sub.1 and 5B.sub.2 respectively. The inner edges of the arm sections are in this embodiment straight, only the outer edges being irregularly tapering as described above. It should be clear that the shape of the arm sections can be chosen and optimized in different ways; only a few advantageous embodiments are shown. The two side edges of an arm section may e.g. taper symmetrically but irregularly, being straight or curved or a combination of both. In other respects similar elements that are illustrated bear the same reference signs as in FIG. 1 but with an index B.

(30) Coaxial connectors 11B.sub.1, 11B.sub.2 for arm sections 1B, 2B are here provided on the first side 5B.sub.1, and coaxial connectors 13B, 13B for arm sections 3B, 4B are here provided on the second side 5B.sub.2. Different mounting elements 17B can be provided for in any appropriate manner in order to allow for easy and reliable mounting of the antenna arrangement wherever desired, for example on the top of a mast, at a micro base station etc. Fastening elements 15B are provided in a convenient manner for mounting circuit boards 16B.sub.1, 16B.sub.2.

(31) FIG. 3A is a top view of antenna arrangement 30 included just to show an example of an advantageous shaping of the arm sections in a clearer manner. Separate openings 6B.sub.1-6B.sub.4 for the connector pins are here provided in the conducting layer of the central portion 5.

(32) FIG. 4 is an illustration of an antenna arrangement 40 with two arm sections 1C, 2C which are bent backwards towards the center of a first side of a central portion 5C such that their end tips will end at a slight diagonal distance from each other at openings 7C.sub.1, 7C.sub.2 through which respective conducting connector pins 6C.sub.1, 6C.sub.2 protrude. The connector pins 6C.sub.1, 6C.sub.2 are connected to microstrip lines 21C, 22C disposed on the second (here under) side of the central portion. The central portion comprises a metal plate from which the arm sections 1C, 2C protrude. The arm sections have a largest width at their ends forming extensions from the central portion, the widths being substantially half of the width of the corresponding outer edge or end of the central portion. The arm sections are disposed diametrically with respect to one another at opposite outer ends of the central portion. In this embodiment the outer edges of an arm section taper substantially symmetrically towards the end tip, although many variations are plausible. Feeding ports 11C, 12C here comprise coaxial connectors 11C.sub.1, 11C.sub.2 arranged at opposite edges of the central portion. Alternatively the connectors could be provided on the first side of the central portion; i.e. on the side on which the arm sections are located. A dielectric layer 9C is arranged between the metal layer of the central portion and the conductors 21C, 21C. Separate openings 7C.sub.1, 7C.sub.2 are provided to enable connection of the end tips with the conductors 21C, 22C. Alternatively there could be a common opening for the connector pins.

(33) FIG. 5 shows an alternative embodiment of a self-grounded antenna arrangement 50 with two arm sections 1D, 2D. The embodiment is similar to that described with reference to FIG. 4 (similar elements bear similar reference numerals but are indexed D), but with the difference that the connectors 11D.sub.1, 11D.sub.2 are disposed close to the same outer side edge of the central portion, which is advantageous from a mounting point of view and for allowing an easy access.

(34) In FIG. 6 still another embodiment of an antenna arrangement 60 comprising two arm sections, forming two antenna elements, is shown. The arm sections 1E, 2E have shapes similar to the shapes of the arm sections of the arrangement shown in FIG. 3. A separate opening 7E.sub.1, 7E.sub.2 is provided for each of the end tips. The conductors 21E, 22E are indicated with dashed lines since they are located on the opposite side of the central portion with respect to the arm sections. Coaxial connectors 11E.sub.1, 11E.sub.2 are conveniently provided close to one another on the first, here upper, side of the central portion 5E as illustrated in FIG. 6.

(35) Arrangements with two or more arm sections bent backwards onto the same side may conveniently be used for wall mounting as a wall antenna with approximately a hemi-spherical coverage.

(36) FIG. 7 shows an embodiment comprising a self-grounded antenna arrangement assembly 70 comprising two antenna arrangements 70A, 70B arranged on a common mounting frame or similar (not shown). The two antenna arrangements 70A, 70B of the assembly 70 are arranged next to each other but they have mirrored geometries as far as the positions of the arm sections are concerned such that an arm section 1E.sub.1 of antenna arrangement 70A is arranged adjacent an arm section 1E.sub.2 on the other antenna arrangement 70B. The connectors (ports) 11.sub.70 for all arm sections are preferably arranged on one and the same side of the arrangement, although they also can be arranged in other manners.

(37) The antenna arrangements 70A, 70B are arranged on each a separate central portion 5E.sub.1, 5E.sub.2, with dielectric layers 9E.sub.1, 9E.sub.2 disposed between respective conductors 21.sub.70 and the conducting material of central portions 5E.sub.1, 5E.sub.2. As in previously described embodiments common openings may be used instead of separate openings in the central portions. An antenna assembly may also comprise more than two antenna arrangements.

(38) Another exemplary assembly 80 is schematically illustrated in FIG. 8, where two arrangements 80A, 80B, which are substantially identical, are disposed close to one another. The first antenna arrangement 80A comprises two arm sections 1F.sub.1, 1F.sub.2, the second antenna arrangement 80B comprises two arm sections 1F.sub.2, 2F.sub.2, the arm sections 2F.sub.1, 1F.sub.2 being arranged on adjacent edge sections of the respective central portions 5F.sub.1, 5F.sub.2 but, here, not facing one another. The four ports 11.sub.80 are arranged on the same side of the central portions of the assembly. In still another embodiment the antenna arrangement has a mirrored geometry (not shown).

(39) It should be clear that such assemblies can be varied in many different ways as discussed in earlier embodiments, e.g. as far as the shape and tapering of the arm sections are concerned, if a common or separate openings are used for the arm sections of an arrangement, the widths and shapes of conductors may be different, where the conductors are located may differ, and the types and arrangement of connectors, as well as the arrangement of the dielectric material on the central portion may be differently implemented. Also the shape of the central portion, although preferably being square shaped or rectangular, may be different and may also have any other shape, for example triangular or hexagonal etc.

(40) FIGS. 9A, 9B show an antenna arrangement 90 comprising a common central portion 5H with four arm sections 1H, 2H, 3H, 4H bent backwards towards the center of the same, first, side 5H.sub.1 of the central portion, separate openings being provided for each end tip. The conductors are indicated through dashed lines in FIG. 9B since they are located on the second, lower side of the central portion. The connectors 11.sub.90 may be disposed in different manners, one specific implementation being shown in FIGS. 9A, 9B. In other respects, shown elements are similar to elements described with reference to the preceding embodiments.

(41) FIG. 10 shows an advantageous embodiment of an antenna arrangement 10K with but one single arm section 1K bent backwards towards a first side of a central portion 5K with, in this embodiment, an opening 7K in a corner thereof. The end tip of the arm section is via connector pin 6K connected to a conductor, for example a microstrip line 25K, illustrated by means of a dashed line, e.g. on a circuit board arranged on a second side of the central portion. A coaxial connector 11K is provided at an outer edge located distant from the end tip and from a transition region of the arm section from the central portion 5K. It should be clear that other conductor types can be used, as well as other types of connectors. The location for a connector may be at the first side of the central portion, or at any other appropriate location.

(42) The arm section 1K may alternatively be bent backwards and face anywhere along the edge opposite the transition region. The central portion may also have another shape and may be larger such that the end tip instead is directed towards any other region of the central portion. The arm section may also have any other shape as discussed with reference to embodiments with two or more arm sections.

(43) FIG. 11 schematically illustrates a non-directional antenna arrangement 92 comprising a central portion 5L with four arm sections, 1L, 2L, 3L, 4L bent backwards towards the center of the same, first, here upper, side 5L.sub.1, of a common central portion 5L. In the central portion 5L, separate openings are provided for the end tips of the respective arm sections 1L, 2L, 3L, 4L. Conductors (not shown) are provided in any appropriate manner on a second side opposite to said first side 5L.sub.1. Connectors (not shown) may be arranged in any appropriate manner as discussed with reference to the other shown embodiments.

(44) FIG. 12A illustrates still another antenna arrangement 95 according to the invention. It comprises three arm sections 1M, 2M, 3M with a common triangular central portion 5M. The arm sections 1M, 2M, 3M comprise symmetrically tapering sections ending with a tip, which are bent backwards onto a first side 5M.sub.1, of the common central portion 5M, the tips pointing towards the center of the central portion and ending at a slight distance from each other and at a slight perpendicular distance from said upper side 5M.sub.1. Connector pins 6M.sub.1, 6M.sub.2, 6M.sub.3 connect the end tips, here via separate openings in the central portion 5M, with conductors (not shown) located on a second side, opposite to said first side, of the central portion. Connectors may be provided as coaxial contacts on one or more side edges of the central portion or in any other convenient manner as discussed with reference to the other illustrated embodiments.

(45) With a three port bow-tie single polarized antenna 95 (i.e. an arrangement with three arms or bows) the coupling between arms may be even further reduced, or a low coupling between ports may be easier to achieve.

(46) Thus, with three arms a particularly compact antenna with a low or substantially no coupling between ports can be provided, e.g. suitable for wall mounting.

(47) It should be clear that the arrangements shown in FIGS. 11, 12, 12A may also be provided as double sided arrangements, i.e. with two such arrangements arranged back-to-back e.g. for mounting on a mast or similar, hence providing for spherical coverage instead of a hemispherical coverage.

(48) FIG. 13 schematically illustrates an implementation in which an arrangement 100 comprising eight separate antenna elements, for example similar to the arm sections described with reference to FIG. 10, via a mounting element 110 is mounted on the top of a mast 101. Connectors 11K.sub.1, 11K.sub.2, . . . are arranged on the edges of respective central portions 5K.sub.1, . . . in order to be easily accessible. In other respects the functioning is the same as that described with reference to the other shown embodiments. In alternative implementations may any other appropriate number of, e.g. three, four, ten, twelve, one-armed antenna sections be arranged on a mast. In still other embodiments, arrangements comprising e.g. two or three arm sections each may be arranged on a mast. Still further it is possible to arrange an arrangement with four or more arm sections having a common central portion on a mast.

(49) FIG. 13A is a schematic view from above of the arrangement 100 shown in FIG. 13.

(50) It is a particular advantage of the invention that antennas with multiple ports are provided which are suitable for MIMO systems, and which are highly uncoupled (such that variations on channels will be different, avoiding that all channels have a low level at the same time).

(51) It is particularly an advantage that an antenna arrangement is provided which is easy to fabricate, mount and control, particularly an UWB-antenna (ultra-wideband).

(52) It is also an advantage that a MIMO antenna which is very small can be made, in some embodiments it may have dimensions corresponding to a cube with an edge length smaller than one third of the lowest operating frequency. It is also an advantage that an antenna arrangement is provided which has a low correlation between different antenna ports when it is used in a statistical field environment with multiphath, e.g. as low as 0.1 over 0.4-16 GHz in an arrangement with four arm sections (antenna elements) although they are located very close to one another. Such a low correlation can be assured by designing the multi-port antenna for having low mutual coupling measured between its ports (i.e. S-parameters S.sub.mn, scattering parameters, smaller than typically 10 dB). It is also an advantage that a large angular coverage can be provided, by all ports together, for example 360 for some implementations, or that antenna elements easily and flexibly can be arranged so as to together provide a desired angular coverage when the received voltages on all ports are combined digitally by a so called MIMO algorithm. An example of such an algorithm is Maximum Ratio Combining (MRC).

(53) The invention is not limited to the illustrated embodiments, but can be varied in a number of ways within the scope of the appended claims.