Antenna arrangement

[0002] The present invention relates to an antenna arrangement for multi frequency band operation, comprising a first radiator element for operation in a first frequency band and a second radiator element for operation in a second frequency band, wherein said second element is arranged in a different plane from said first element. The invention also relates to an array antenna arrangement comprising groups of first and second elements. Also, the invention relates to the use of such an antenna arrangement.

[0003] A large number of base station antenna installations have been necessary for the operation of cellular mobile telecommunication systems. Base station antenna arrangements have to be provided all over the area that is to be covered by the cellular communication system and how they are arranged among other things depends on the quality that is required and the geographical coverage, the distribution of mobile units etc. Since radio propagation depends very much on terrain and irregularities in the landscape and the cities the base station antenna arrangements have to be arranged more or less closely.

[0004] However, the installation of multiple antenna base stations has caused protests among others from an esthetical point of view both on the countryside and in the cities. Also, the construction of these antenna masts is expensive, e.g. because each antenna needs to be supplied with energy via a separate, expensive feeding cable.

[0005] The introduction of new base station antenna arrangements would be considerably facilitated if the infrastructure that already is in place could be better used. Today various examples of microstrip antenna elements which are capable of operating in two distinct frequency bands are known. However, it is difficult to avoid grating lobes when the frequency bands are not closely spaced.

[0006] An object of the invention is therefore to provide a multi frequency band antenna which does not present the above described problems. Another object of the invention is to provide an antenna which operates with different polarization states.

[0007] For these objects, the antenna arrangement in accordance with the invention is characterized in accordance with the accompanying independent claims.

[0008] Advantageous embodiments of the invention are described in the accompanying depending claims.

[0009] It is an advantage of the invention that the existing infrastructure already provided for the 800 or 900 MHz frequency band can be used also for new frequency bands such as about 1800 MHz or 1900 MHz. It is also an advantage of the invention that the antenna elements or the radiating elements are simple and flexible and enables a simple feeding etc. It is also an advantage that dual polarization states can be supported with a high mutual insulation.

[0010] The invention will be further described in the following in a non-limiting way under reference to the accompanying drawings in which:

[0011] FIG 1ais a top view of a multi frequency antenna arrangement according to the invention,

[0012] FIG 1bis a schematical cross-sectional view of the antenna of FIG. 1A along the lines 1b—1b,

[0013] FIG. 2ais a top view of an alternative embodiment of an antenna according to the invention,

[0014] FIG. 2bis a schematical cross-sectional view of the antenna of FIG. 2A along the lines 2b—2b,

[0015] FIG. 3ais a top view of a third embodiment of an antenna according to the invention,

[0016] FIG. 3bis a cross-sectional view of the arrangement of FIG. 3A along the lines 3B—3B, and

[0017] FIG. 4 is a top view of an array antenna according to the invention.

[0018] FIGS. 1aand 1billustrate a first example of a microstrip antenna which is able to operate (receive/transmit) at two different frequencies or in two different frequency bands simultaneously. In FIG. 1a, which is a top view of the antenna, a first radiating element 10 is arranged on top. The first radiating element 10 is here square shaped. A second radiating element 11 is arranged below the first radiating element. The second radiating element is symmetrically arranged in a centralized manner under the first radiating element. The first and second radiating elements 10, 11 respectively particularly comprise so called patch elements made of a conducting material, for example Cu.

[0019] The first patch element or radiating element 10 may be used for a communication system operating in frequency band of about 1800-1900 MHz whereas the second radiating element 11 may be used for a communication system operating in the frequency band of about 800-900 MHz. To facilitate this, the first and the second radiating elements have the appropriate effective resonant dimension respectively, in accordance with common practice, and in view of the effective dielectric constant of the dielectric material or medium, e.g. air which is used for insulating the first and the second patch.

[0020] In FIGS. 1a, 1bthe first radiating element 10 is mounted on two orthogonally arranged pairs of probes 12 that are responsible for energizing this element in two directions of polarization with a mutual angle of about 90°. The probes 12 extend via holes through the second element 11 and are mounted on a first layer 13 of a ground plane that also comprises a second layer 14. The ground plane layer 13 is provided with an electric feed network 15 for supplying the probes with energy in the two angles of polarization.

[0021] The lower, second radiating element, i.e. the low frequency band patch 11 is aperture fed from the second ground plane layer 14 via an aperture arrangement comprising slots 16 and 17. The outer slots 16 are oriented according to one of the polarization angles and the inner H-shaped slot 17 is oriented according to the other angle. The polarization is perpendicular to the long dimension of the slots. The ground plane layer 14 is provided with an electric feed net 18 for supplying the slots with energy in the two angles of polarization. The above described slot configuration is only one example, many alternative slot configurations are possible, for example with crossing slots.

[0022] In alternative embodiments of the above described antenna, the second element may be energized by probes and this element may be provided with slot apertures for energizing the first element. The patches may have other shapes than square. The antenna may comprise any number of stacked elements for different frequencies, depending on the number of frequencies to be used in the antenna. The above described antenna module may be used in a multiple module array antenna.

[0023] In the above described embodiment, it is possible to feed both patches by means of the four probes 12. In this manner, a single power feed network may be used for energizing both patches.

[0024] FIGS. 2aand 2bshow an alternative example of a microstrip antenna which is able to operate (receive/transmit) at two different frequencies or in two different frequency bands simultaneously. The same reference numbers have been used as in FIG. 1aand 1bto designate the corresponding details.

[0025] As in the first embodiment of the invention, in FIG. 2a, which is a top view of the antenna, a first radiating element 10 is arranged on top. A second radiating element 11 is arranged below the first radiating element, symmetrically arranged in a centralized manner under the first radiating element.

[0026] The first patch element or radiating element 10 may be used for a communication system operating in frequency band of about 1800-1900 MHz whereas the second radiating element 11 may be used for a communication system operating in the frequency band of about 800-900 MHz.

[0027] In FIGS. 2a, 2bthe first radiating element 10 is mounted on two orthogonally arranged pairs of probes 12athat are responsible for energizing this element in two directions of polarization with a mutual angle of about 90. The probes 12aextend via holes through the second element 11 and are mounted on a first layer 13 of a ground plane that also comprises a second layer 14. The ground plane layer 13 is provided with an electric feed net 15 for supplying the probes with energy in the two angles of polarization.

[0028] The lower, second radiating element, i.e. the low frequency band patch 11 is probe fed from the second ground plane layer 14 via probes 12b. Thus, the patch 11 is mounted on two orthogonally arranged pairs of probes 12b. One pair of probes 12bis oriented according to one of the polarization angles and the other pair of probes is oriented according to the other angle. The ground plane layer 14 is provided with an electric feed net 18 for supplying the probes with energy in the two angles of polarization.

[0029] In alternative embodiments of the above described antenna, the patches may have other shapes than square. The antenna may comprise any number-of stacked elements for different frequencies, depending on the number of frequencies to be used in the antenna. The above described antenna module may be used in a multiple module array antenna.

[0030] FIGS. 3aand 3bshow a third example of a microstrip antenna in accordance with the invention which is able to operate (receive/transmit) at two different frequencies or in two different frequency bands simultaneously. The same reference numbers have been used as in FIGS. 1a, 1b, 2aand 2bto designate the corresponding details.

[0031] As in the first embodiment of the invention, in FIG. 3a, which is a top view of the antenna, a first radiating element 10 is arranged on top. A second radiating element 11 is arranged below the first radiating element, symmetrically arranged in a centralized manner under the first radiating element.

[0032] The first patch element or radiating element 10 may be used for a communication system operating in frequency band of about 1800-1900 MHz whereas the second radiating element 11 may be used for a communication system operating in the frequency band of about 800-900 MHz.

[0033] In FIGS. 3a, 3bthe first radiating element 10 is energized via aperture slots 16aand 17ain the second radiating element 11. The outer slots 16aare oriented according to one of the polarization angles and the inner H-shaped slot 17ais oriented according to the other angle. The element 11 is provided with an electric feed net 15afor supplying the aperture slots with energy in the two angles of polarization.

[0034] The lower, second radiating element, i.e. the low frequency band patch 11 is aperture fed from the ground plane 14 via slots 16band 17b. The outer slots 16bare oriented according to one of the polarization angles and the inner H-shaped slot 17bis oriented according to the other angle. The polarization is perpendicular to the long dimension of the slot. The ground plane layer 14 is provided with an electric feed net 15bfor supplying the slots with energy in the two angles of polarization.

[0035] In alternative embodiments of the above described antenna, the patches may have other shapes than square. The antenna may comprise any number of stacked elements for different frequencies, depending on the number of frequencies to be used in the antenna. The above described antenna module may be used in a multiple module array antenna. The second element 11 may be designed so that it is transparent with reference to the frequency of the first element 10, by e.g. incorporating FSS (Frequency Sensitive Surface) technics. In this way it is possible to have the slots for the two elements in a common ground plane.

[0036] FIG. 4 shows an array antenna in accordance with the invention, which in this example comprises three groups of elements, but any number of such groups is possible. Two of the element groups are similar to the example shown in FIGS. 1aand 1b. Between these two element groups is a third element group comprising an extra element 10 of the first high frequency type. This configuration may be suitable for avoiding grating lobes. The ground plane 14apreferably continues below the central group of elements, and the ground plane 14bof the central high frequency patch 10 preferably is arranged at the same level as the second elements 11 of the two lateral groups of elements. The central high frequency patch 10 is powered by probes 12.

[0037] The elements in FIG. 4 are oriented so that the polarization directions are ±45° with respect to the long dimension of the array. Any other directions, e.g. 0° and 90° may be used. The element groups of the array antenna may also be arranged in two dimensions.

[0038] In any of the above described antennas the two linear polarizations may be combined to form one or two circular. polarizations.

[0039] The invention is of course not limited to the shown embodiments but it can varied in a number of ways only being limited by the scope of the claims. For example, any number of probes may be used in the antenna as long as they are symmetrically oriented around the axes of polarization. Rectangular, circular, oval or any other form of patches may be used.