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.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an antenna arrangement having the features of the first part of claim  1 . 
         [0002]    The invention also relates to a method for producing an antenna arrangement having the features of the first part of claim  29 . 
       BACKGROUND 
       [0003]    There is an increasing demand of wideband antennas in wireless communication devices, in order to allow communication in several frequency bands and for different systems. Ultra Wide Band (UWB) signals are generally defined as signals having a large relative bandwidth (bandwidth divided by carrier frequency) or a large absolute bandwidth. The expression UWB is particularly used for the frequency band 3.2-10.6 GHz, but also for other and wider frequency bands. 
         [0004]    The use of wideband signals is associated with many positive aspects and advantages as for example described in “History and applications of UWB”, y M. Z. Win et.al, Proceedings of the IEEE, vol. 97, No. 2, p. 198-204, February 2009. 
         [0005]    Another important aspect of the UWB-technology is that it is a low cost technology. Recent development of CMOS processors transmitting and receiving UWB-signals has opened up for a large field of different applications and they can be fabricated at a very low cost for UWB-signals without requiring any hardware for mixers, RF (Radio Frequency)-oscillators or PLLs (Phase Locked Loops). 
         [0006]    UWB technology can be implemented in a wide range of areas, for different applications, such as for example short range communication (less than 10 m) with extremely high data rates (up to or above 500 Mbps), e.g. for wireless USB similar communication between components in entertainment systems such as DVD players, TV and similar; in sensor networks where low data rate communication is combined with precise ranging and geolocation, and radar systems with extremely high spatial resolution and obstacle penetration capabilities, and generally for wireless communication devices. 
         [0007]    It is challenging to generate, transmit, receive and process UWB signals, since it requires the development of new techniques and arrangements within the fields of generation of signals, signal transmission, signal propagation, signal processing and system architectures. 
         [0008]    Basically UWB antennas can be divided into four different categories. The first category comprises a so called scaled category, comprising bow-tie dipoles, see for example “A modified Bow-Tie antenna for improved pulse radiation”, by Lestari et.al, IEEE Trans. Antennas Propag., Vol. 58, No. 7, pp. 2184-2192, July 2010, biconical dipoles as for example discussed in “Miniaturization of the biconical Antenna for ultra wideband applications” by A. K. Amert et. al, IEEE Trans. Antennas Propag., Vol. 57, No. 12, pp. 3728-3735, December 2009. 
         [0009]    The second category comprises so called self-complementary structures as e.g. described in “Self-complementary antennas” by Y. Mushiake, IEEE Antennas Propag. Mag., vol. 34, No. 6, pp. 23-29, December 1992. The third category comprises travelling wave structure antennas, e.g. the so called Vivaldi antenna which is a well known and widely used antenna, as e.g. discussed in “The Vivaldi aerial” by P. J. Gibson, Proc. 9 th  European Microwave conference, pp. 101-105, 1979. The fourth category comprises multiple resonance antennas like log-periodic dipole antenna arrays. 
         [0010]    Antennas from the scaled category, the self-complementary category and the multiple reflection category comprise compact, low profile antennas with low gain, i.e. having wide and often more or less omni-directional far field patterns, whereas antennas of the travelling wave category, like the Vivaldi antennas, are directional. 
         [0011]    The above-mentioned UWB antennas were mainly designed for use in normal Line-of-Sight (LOS) antenna systems with one port per polarization and a known direction of the single wave between the transmitting and receiving side of the communication system. 
         [0012]    However, most environments have many objects (such as houses, trees, vehicles, humans) between the transmitting and receiving sides of the communication systems that cause reflections and scattering of the waves, resulting in a multiple of incoming waves on the receiving side. Interference between these waves causes large level variations known as fading of the received voltage (known as the channel) at the port of the receiving antenna. This fading can be counteracted in modern digital communication systems that make use of multiport antennas and support MIMO technology (multiple-input multiple-output). However, so far, there exists no wideband multiport antenna suitable for such MIMO communication systems. 
         [0013]    Future wireless communication systems are supposed to comprise a large number of micro base stations with multiband multiport antennas enabling MIMO. Known solutions do not meet requirements as to compactness, angular coverage, radiation efficiency and polarization schemes, which all are critical issues for the performance of such systems. The radiation efficiency of a multiport antenna is reduced by ohmic losses and impedance mismatch like in single-port antennas, but also by mutual coupling between the antenna ports. Therefore, this mutual coupling should be low, but there is not known any compact multiport antenna with low mutual coupling between the ports. 
         [0014]    The bow-tie antenna described in SE 535 251 is a single port directional UWB antenna and does not solve the problems referred to above. 
       SUMMARY 
       [0015]    It is therefore an object of the present invention to provide an antenna arrangement through which one or more of the above mentioned problems can be solved. It is particularly an object to provide an antenna arrangement suitable for micro base stations for wireless communication through which multipath fading effects can be reduced. Particularly it is an object to provide an antenna arrangement which is easy and cheap to fabricate, most particularly an UWB multiport antenna for a MIMO system. 
         [0016]    Another object is to provide an antenna arrangement, most particularly an UWB multiport antenna, which is suitable for use in measurement systems for wireless devices with or without MIMO capability, such as measurement systems based on reverberation chambers. 
         [0017]    Therefore an arrangement as initially referred to is provided which has the characterizing features of claim  1 . 
         [0018]    Still further it is an object of the present invention to provide a method for fabrication of an antenna arrangement through which one or more of the above mentioned objects can be achieved. It is in particular an object to provide a method which is easy to carry out, which involves only low costs, which is reliable and repeatable. Therefore a method as initially referred to is provided which has the characterizing features of claim  29 . 
         [0019]    Advantageous embodiments are given by the respective appended dependent claims. 
         [0020]    Particularly a multiport antenna is provided for which the mutual coupling between the antenna ports is weak, so that the far field functions become almost orthogonal. According to the invention is particularly provided an UWB multiport antenna arrangement with a weak mutual coupling between the antenna ports ensuring far field functions that are orthogonal in some sense, such as in terms of polarization, direction or shape. With orthogonal is here meant that the inner products of the complex far field functions are low over the desired coverage of the antennas. Particularly, there is also provided an UWB antenna arrangement for measurement systems for wireless devices of wireless systems, with or without MIMO capability, which has multiple ports, with a weak coupling, particularly no coupling at all, or at least a coupling which is as low as possible between them and far field functions which are orthogonal. The invention is particularly advantageous for use in MIMO antenna systems for statistical multipath environments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The invention will in the following be further described in a non-limiting manner, and with reference to the accompanying drawings, in which: 
           [0022]      FIG. 1  is a view of an antenna arrangement according to a first embodiment of the present invention with four antenna ports, 
           [0023]      FIG. 1A  is a side view of the arrangement in  FIG. 1 , 
           [0024]      FIG. 1B  shows an arrangement as in  FIG. 1  which is slightly modified, 
           [0025]      FIG. 2  shows a second embodiment of an antenna arrangement according to the invention, 
           [0026]      FIG. 3  is a view of a third embodiment of an arrangement according to the invention here, also with four antenna ports, 
           [0027]      FIG. 3A  is a top view of the arrangement of  FIG. 3 , 
           [0028]      FIG. 4  is a view of a fourth embodiment comprising an antenna arrangement with two antenna ports, 
           [0029]      FIG. 5  is a schematic view of a fifth embodiment comprising an arrangement with two arms, 
           [0030]      FIG. 6  schematically illustrates an arrangement according to the invention suitable for mounting on a wall, 
           [0031]      FIG. 7  schematically illustrates another arrangement according to the invention which comprises two antenna structures and which is suitable for wall mounting, 
           [0032]      FIG. 8  schematically illustrates another embodiment of an arrangement comprising two antenna structures and which also is suitable for wall mounting, 
           [0033]      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, 
           [0034]      FIG. 9B  is a top view of the arrangement in  FIG. 9A , 
           [0035]      FIG. 10  illustrates an embodiment with an antenna arrangement comprising one port and a single arm section, 
           [0036]      FIG. 11  shows still another embodiment of an arrangement comprising four arms and corresponding ports, 
           [0037]      FIG. 12A  is a top view of an arrangement comprising three arms and three ports, 
           [0038]      FIG. 12B  is a perspective view of the arrangement shown in  FIG. 12A , 
           [0039]      FIG. 13  schematically illustrates an arrangement with spherical coverage and which is suitable for mounting on a mast, 
           [0040]      FIG. 13A  is a top view of the arrangement in  FIG. 13 . 
       
    
    
     DETAILED DESCRIPTION 
       [0041]      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   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   1 . The end tips are connected to connector pins  6   1 ,  6   2  which via separate openings  7   1 ,  7   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 . 
         [0042]    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   1  of the central portion and extend in substantially opposite directions towards outer side edges of the central portion. Ports  11   1 - 11   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. 
         [0043]    The central portion  5  comprises a metal layer  9 , on part of the surfaces of which dielectric layers forming printed circuit boards  9   1 ,  9   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   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. 
         [0044]    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. 
         [0045]    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   1  of the central portion whereas the second arm portions  3 ,  4  are bent backwards towards the second side  5   2  of the central portion  5 . The end tips of the arm sections are connected to connector pins  6   1 ,  6   2 ,  6   3 ,  6   4  via respective openings connecting to microstrip conductors on the respective opposite sides of the central portion. 
         [0046]    In the embodiment of  FIG. 1A  the dielectric layers  9   1 ,  9   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. 
         [0047]      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. 
         [0048]      FIG. 2  illustrates an antenna arrangement  20  also comprising four arm sections  1 A,  2 A,  3 A,  4 A as in  FIG. 1 . Elements similar to elements shown in  FIGS. 1 ,  1 A are given the same reference numerals but with an index “A”. In the arrangement  20  the conductor elements  21 A,  22 A,  23 A,  24 A are all arranged to be directed towards the same side edge of the central portion  5 A enabling the provisioning of connectors, e.g. coaxial connectors  11 A 1 - 11 A 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  5 A 1 ,  5 A 2  respectively, or in any appropriate manner; the invention is not limited to any particular type of connectors or connector locations. 
         [0049]    The antenna arrangement  30  shown in  FIG. 3  also comprises four arm sections  1 B,  2 B,  3 B,  4 B extending from a central portion  5 B which are diametrically and pairwise bent backwards onto a first side  5 B 1  and onto a second side  5 B 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  5 B 1  and  5 B 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. 
         [0050]    Coaxial connectors  11 B 1 ,  11 B 2  for arm sections  1 B,  2 B are here provided on the first side  5 B 1 , and coaxial connectors  13 B,  13 B for arm sections  3 B,  4 B are here provided on the second side  5 B 2 . Different mounting elements  17 B 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  15 B are provided in a convenient manner for mounting circuit boards  16 B 1 ,  16 B 2 . 
         [0051]      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  6 B 1 - 6 B 4  for the connector pins are here provided in the conducting layer of the central portion  5 . 
         [0052]      FIG. 4  is an illustration of an antenna arrangement  40  with two arm sections  1 C,  2 C which are bent backwards towards the center of a first side of a central portion  5 C such that their end tips will end at a slight diagonal distance from each other at openings  7 C 1 ,  7 C 2  through which respective conducting connector pins  6 C 1 ,  6 C 2  protrude. The connector pins  6 C 1 ,  6 C 2  are connected to microstrip lines  21 C,  22 C disposed on the second (here under) side of the central portion. The central portion comprises a metal plate from which the arm sections  1 C,  2 C 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  11 C,  12 C here comprise coaxial connectors  11 C 1 ,  11 C 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  9 C is arranged between the metal layer of the central portion and the conductors  21 C,  21 C. Separate openings  7 C 1 ,  7 C 2  are provided to enable connection of the end tips with the conductors  21 C,  22 C. Alternatively there could be a common opening for the connector pins. 
         [0053]      FIG. 5  shows an alternative embodiment of a self-grounded antenna arrangement  50  with two arm sections  1 D,  2 D. 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  11 D 1 ,  11 D 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. 
         [0054]    In  FIG. 6  still another embodiment of an antenna arrangement  60  comprising two arm sections, forming two antenna elements, is shown. The arm sections  1 E,  2 E have shapes similar to the shapes of the arm sections of the arrangement shown in  FIG. 3 . A separate opening  7 E 1 ,  7 E 2  is provided for each of the end tips. The conductors  21 E,  22 E 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  11 E 1 ,  11 E 2  are conveniently provided close to one another on the first, here upper, side of the central portion  5 E as illustrated in  FIG. 6 . 
         [0055]    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. 
         [0056]      FIG. 7  shows an embodiment comprising a self-grounded antenna arrangement assembly  70  comprising two antenna arrangements  70 A,  70 B arranged on a common mounting frame or similar (not shown). The two antenna arrangements  70 A,  70 B 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  1 E 1  of antenna arrangement  70 A is arranged adjacent an arm section  1 E 2  on the other antenna arrangement  70 B. The connectors (ports)  11   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. 
         [0057]    The antenna arrangements  70 A,  70 B are arranged on each a separate central portion  5 E 1 ,  5 E 2 , with dielectric layers  9 E 1 ,  9 E 2  disposed between respective conductors  21   70  and the conducting material of central portions  5 E 1 ,  5 E 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. 
         [0058]    Another exemplary assembly  80  is schematically illustrated in  FIG. 8 , where two arrangements  80 A,  80 B, which are substantially identical, are disposed close to one another. The first antenna arrangement  80 A comprises two arm sections  1 F 1 ,  1 F 2 , the second antenna arrangement  80 B comprises two arm sections  1 F 2 ,  2 F 2 , the arm sections  2 F 1 ,  1 F 2  being arranged on adjacent edge sections of the respective central portions  5 F 1 ,  5 F 2  but, here, not facing one another. The four ports  11   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). 
         [0059]    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. 
         [0060]      FIGS. 9A ,  9 B show an antenna arrangement  90  comprising a common central portion  5 H with four arm sections  1 H,  2 H,  3 H,  4 H bent backwards towards the center of the same, first, side  5 H 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   90  may be disposed in different manners, one specific implementation being shown in  FIGS. 9A ,  9 B. In other respects, shown elements are similar to elements described with reference to the preceding embodiments. 
         [0061]      FIG. 10  shows an advantageous embodiment of an antenna arrangement  10 K with but one single arm section  1 K bent backwards towards a first side of a central portion  5 K with, in this embodiment, an opening  7 K in a corner thereof. The end tip of the arm section is via connector pin  6 K connected to a conductor, for example a microstrip line  25 K, 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  11 K 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  5 K. 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. 
         [0062]    The arm section  1 K 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. 
         [0063]      FIG. 11  schematically illustrates a non-directional antenna arrangement  92  comprising a central portion  5 L with four arm sections,  1 L,  2 L,  3 L,  4 L bent backwards towards the center of the same, first, here upper, side  5 L 1 , of a common central portion  5 L. In the central portion  5 L, separate openings are provided for the end tips of the respective arm sections  1 L,  2 L,  3 L,  4 L. Conductors (not shown) are provided in any appropriate manner on a second side opposite to said first side  5 L 1 . Connectors (not shown) may be arranged in any appropriate manner as discussed with reference to the other shown embodiments. 
         [0064]      FIG. 12A  illustrates still another antenna arrangement  95  according to the invention. It comprises three arm sections  1 M,  2 M,  3 M with a common triangular central portion  5 M. The arm sections  1 M,  2 M,  3 M comprise symmetrically tapering sections ending with a tip, which are bent backwards onto a first side  5 M 1 , of the common central portion  5 M, 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  5 M 1 . Connector pins  6 M 1 ,  6 M 2 ,  6 M 3  connect the end tips, here via separate openings in the central portion  5 M, 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. 
         [0065]    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. 
         [0066]    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. 
         [0067]    It should be clear that the arrangements shown in  FIGS. 11 ,  12 ,  12 A 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. 
         [0068]      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  11 K 1 ,  11 K 2 , . . . are arranged on the edges of respective central portions  5 K 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. 
         [0069]      FIG. 13A  is a schematic view from above of the arrangement  100  shown in  FIG. 13 . 
         [0070]    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). 
         [0071]    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). 
         [0072]    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 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). 
         [0073]    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.