Patent Application
20100149068
The present invention relates to a dual polarized array antenna comprising at least two dual polarized antenna elements being arranged for radiating electromagnetic energy having a first polarization, constituting a first antenna radiation pattern, via a connection to a first antenna port, and electromagnetic energy having a second polarization, constituting a second antenna radiation pattern, via a connection to a second antenna port, the second polarization being orthogonal to the first polarization, the first antenna radiation pattern and second antenna radiation pattern each having a main beam and a number of side-lobes with nulls positioned at angular positions between a side-lobe and an adjacent side-lobe or the main beam when adjacent.
For mobile communication transmissions of today, such as MIMO, it is often desirable to use dual polarized antennas. Generally, a dual polarized antenna comprises a first number of first antenna elements, having a first polarization, and a second number of second antenna elements having a second polarization. Normally, the first and second numbers are equal, and the first polarization and second polarization are mutually orthogonal, constituting a number of dual polarized antenna elements. The first antenna elements are connected to a first antenna beam port, and the second antenna elements are connected to a second antenna beam port. Depending on the number of antenna elements, corresponding distribution networks are used.
Often the first and the second polarizations are provided with dual orthogonal polarized antenna elements, where the first polarization is associated with the first antenna beam port and the second polarization is associated with the second antenna beam port.
The antenna radiation patterns of the antenna elements of each polarization may be tilted electrically by feeding each antenna element with a certain phase. Such an electrical tilt requires that at least two antenna elements are used for each polarization. The electrical tilt may be fixed or adjustable, and set by means of how the distribution network is designed. In some cases also a certain amplitude is applied to each antenna element for side-lobe control.
For each polarization of a dual polarized sector covering antenna having a number of antenna elements in a vertical column, there is normally a broad coverage in azimuth, perpendicular to the longitudinal extension of the antenna column, in a broad main antenna beam. In elevation, along the longitudinal extension of the antenna column, there is normally a relatively narrow coverage in a narrow antenna beam with adjacent side-lobes. In so-called null directions in elevation there is a very low antenna gain, between the side-lobes. In these directions, so-called nulls are present in the antenna radiation pattern. These nulls are present for both polarizations. Consequently, the path-gain is quite low in these null directions.
It is desirable to increase the path-gain in the null directions, with maintained orthogonality between the two radiation patterns comprised in the array antenna.
In WO 2006/065172 single polarized sub-array antennas, each sub-array antenna comprising a number of antenna elements having a certain polarization, are mounted in such a way that they constitute a total array antenna. It is suggested that a sub-array having a different polarization is mixed with the others in order to provide null-fill.
The document WO 2006/065172 only concerns a single polarized antenna, and the proposed solution for null-fill requires one additional sub-array.
There is thus a need for a dual polarized antenna with increased path-gain in the null directions, with maintained orthogonality between the polarizations.
The object of the present invention is to provide a dual polarized antenna with mutually orthogonal polarizations which is arranged for increased path-gain in the null directions, with maintained orthogonality between the polarizations.
Said object is achieved by means of a dual polarized array antenna as mentioned initially. The array antenna furthermore comprises at least one further dual polarized antenna element, being arranged for radiating electromagnetic energy having two mutually orthogonal polarizations, constituting further antenna radiation patterns, via respective connections to the first antenna port and the second antenna port, where the polarization of said at least one further dual polarized antenna element that is associated with the first antenna port deviates from the first polarization and at least one null of the first antenna radiation pattern has a different angular position than any null of that further antenna radiation pattern that is radiated via the first antenna port, such that said at least one null of the first antenna pattern is at least partly filled.
In a preferred embodiment, the array antenna comprises at least two further dual polarized antenna elements, where those polarizations of said further dual polarized antenna elements that are associated with the first antenna port have differently rotated orientations.
In another preferred embodiment, a polarization of said at least one further dual polarized antenna element which is associated with the first antenna port, is orthogonal to the first polarization.
In another preferred embodiment, those polarizations which are associated with the first antenna port are associated with said first antenna port via a first distribution network, and that those polarizations which are associated with the second antenna port are associated with said second antenna port via a second distribution network.
In another preferred embodiment, the distribution networks are arranged in such a way that they provide a certain phase taper and/or amplitude taper to the dual polarized antenna elements.
In another preferred embodiment, said dual polarized antenna elements are arranged in a column.
Further preferred embodiments are apparent from the dependent claims.
A number of advantages are obtained from the present invention. For example:
The present invention will now be described more in detail with reference to the appended drawing, where
In
With reference also to
As shown in detail in
An example of a slot feed comprising a fork-shaped slot feed is shown in the prior art document U.S. Pat. No. 6,018,320.
As previously known, patches in the form of metal squares (not shown) may be placed a certain distance above the slots in order to increase the bandwidth, resulting in aperture-fed patch elements.
The distances between the nine antenna elements 2, 3, 4, 5, 6, 7, 8, 9, 10 are equal and chosen in such a way that grating lobes do not appear.
The horizontally polarized slots 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h of the first eight antenna elements 2, 3, 4, 5, 6, 7, 8, 9 from the first end 12 are fed by a first distribution network, which is designed in such a way that the slots 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h are fed with the same phase and with the same amplitude.
According to the present invention, the vertically polarized slot 22v of the ninth antenna element 10 from the first end 12, placed adjacent to the second end 13, is also fed by the first distribution network.
The first distribution network divides or sums power from and to a first antenna port 28, depending on if the first antenna port 28 is transmitting or receiving. For simplicity, in the following, it is assumed that the array antenna 1 is transmitting. Thus, a signal that is applied to the first antenna port 28 is distributed to the horizontally polarized slots 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h of said first eight antenna elements 2, 3, 4, 5, 6, 7, 8, 9 and the vertically polarized slot 22v of the ninth antenna element 10, where all slots 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22v, are fed in the same phase and with the same amplitude.
The antenna radiation pattern in elevation radiated by the first eight slots 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, along the height of the column 11, has nulls in angular directions between a main beam and all side-lobes. The antenna radiation pattern radiated by the ninth slot 22v, in the same elevation cut as the first eight slots 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, does not have nulls in the same angular directions as the antenna radiation pattern radiated by the first eight slots 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h. Thus the differently polarized ninth slot 22v performs null-filling of the power radiation pattern radiated by the first eight slots 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, as shown in
On the x-axis, the elevation angle in degrees is shown, and on the y-axis, the normalized gain in dB is shown. The resulting polarization of the signal at the first antenna port 28 is not completely horizontal, but rotated due to the ninth vertically polarized slot 22v. In this way, null-filling is performed for the signal at the first antenna port 28.
In the same way as described above, the remaining nine slots 14v, 15v, 16v, 17v, 18v, 19v, 20v, 21v, 22h are connected to a second distribution network, which is connected to a second antenna port 29. Thus, a signal that is applied to the second antenna port 29 is distributed to the vertically polarized slots 14v, 15v, 16v, 17v, 18v, 19v, 20v, 21v of the first eight antenna elements 2, 3, 4, 5, 6, 7, 8, 9 and the horizontally polarized slot 22h of the ninth antenna element 10, where all slots 14v, 15v, 16v, 17v, 18v, 19v, 20v, 21v, 22h are fed with the same phase and with the same amplitude when the ninth dual polarized antenna element is rotated 90°. In this way, null-filling is performed for the signal at the second antenna port 29 in the same way as described for the first antenna port 28. The resulting polarization of the signal at the second antenna port 29 is not completely vertical, but rotated due to the ninth horizontally polarized slot 22h.
In this manner, the polarization orthogonality is maintained between the radiation patterns of the first antenna port 28 and the second antenna port 29, since the ninth antenna element 10 rotates the respective polarization to the same extent, and similar amplitude and phase characteristics are applied to the antenna elements by the first and second distribution networks.
The ninth antenna element 10 in the example described above thus constitutes a null-filling antenna element, filling the nulls by having a polarization orientation different from the rest of the antenna elements 2, 3, 4, 5, 6, 7, 8, 9 of the array antenna 1.
It is necessary to feed the ninth respective slots 22v, 22h with an adapted phase and/or amplitude in order to obtain a desired null-fill, but it is important that the same relative phase and amplitude is applied for both slots 22v, 22h of the ninth antenna element 10, when it is rotated 90°, in order to maintain orthogonality.
The embodiment example described above with reference to
The polarizations of a null-filling dual polarized antenna element 10 do not have to be orthogonal to the polarization of the respective other antenna elements 2, 3, 4, 5, 6, 7, 8, 9. In
Here, however, the seventh dual polarized antenna element 38 is rotated an angle a with respect to the other dual polarized antenna elements 32, 33, 34, 35, 36, 37, 39, 40. This means that the seventh dual polarized antenna element 38, constituting a null-filling antenna element, comprises two orthogonal slots 38a, 38b, which are rotated an angle a with respect to the slots of the other dual polarized antenna elements.
The difference between
Generally, a resulting polarization component of the null-filling antenna element 10, 38 that is orthogonal to the co-polarized component of the other antenna elements 32, 33, 34, 35, 36, 37, 39, 40, contributes to filling at least one null in the radiation pattern related to the co-polarized component of the other antenna elements 32, 33, 34, 35, 36, 37, 39, 40, when said resulting polarization component of the null-filling antenna element 10, 38 interferes with the co-polarized component of the other antenna elements 32, 33, 34, 35, 36, 37, 39, 40.
Furthermore, it should be understood that a horizontal polarization or vertical polarization is not exact due to manufacturing errors and environmental factors. In the context of the present invention, all polarizations are mentioned as they are intended to be in the ideal case, although their exact appearance may be inexact. In the present invention, null-filling antenna elements are intended to have polarizations associated with respective antenna ports that differ from the polarizations of the other antenna elements connected to said respective antenna ports.
The main concept of the present invention is to provide two superimposed antenna radiation patterns for each antenna port 28, 29, where some or all nulls of these antenna radiation patterns do not coincide.
The invention is not limited to the embodiment example above, but may vary freely within the scope of the appended claims.
For example, the dual orthogonal polarized antenna elements 2, 3, 4, 5, 6, 7, 8, 9, 10 may be comprised of any suitable type of radiating structures which can generate linear, circular or elliptical polarization, for example patches, dipoles or a combination thereof.
Furthermore, an ordinary amplitude and/or phase taper may be used in order to, for example, obtain desired side-lobe levels in combination with the present invention. A linear phase taper may be used to obtain a desired beam tilt. Phase shifts may be implemented by means of time delays. Of course, these techniques may be combined.
The distance between the antenna elements 2, 3, 4, 5, 6, 7, 8, 9, 10 may also be chosen such that grating lobes do appear, the array antenna thus constituting a so-called sparse array antenna.
The antenna elements 2, 3, 4, 5, 6, 7, 8, 9, 10 may be non-uniformly spaced.
The distribution networks used may be in any other suitable form than the microstrip distribution network described. Coaxial cables and discrete power divider elements may for example be used. Preferably, the distribution networks connected to the antenna ports 28, 29 have the same mutual phase and amplitude characteristics.
The antenna column 11 shown has been vertically oriented, but any orientation of such an antenna column is conceivable.
With reference to
With reference to
If there is more than one null-filling antenna element in an array antenna, their polarizations may differ. In other words, the null-filling elements' polarizations may be mutually rotated for some or all null-filling elements used.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE07/50302 | 5/4/2007 | WO | 00 | 11/4/2009 |
